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This Vacuum Controller switches on a vacuum when an appliance such as a circular saw is started. It runs the vacuum for a preset period after the appliance is switched off to draw up remaining dust. It includes optional blast gate control, and interlinking between units, for use with more than one tool. John Clarke’s Vacuum Cont V acuuming up dust produced by woodworking machinery is a necessity for cleanliness, safety and health reasons. Manufactured and natural timber dust can be toxic or become an irritant to the lungs if breathed in, ultimately causing health problems. Dust from timbers such as western red cedar can increase the risk of developing throat cancer. Wearing a face mask limits the amount of dust entering the lungs. However, fine dust in the air can also become an explosion hazard. Ideally, this dust should be vacuumed up as it is produced, to minimise airborne wood particle dust. Besides, who wants to clean up a workshop full of sawdust after doing some work? Incidentally, vacuuming air through ducting tubes made from metal or plastic can cause an electrostatic charge to build. If not Earthed, the charge buildup can produce sparks, resulting in dust explosions. It is important to provide Earthing for metal ducting and include Earthed bare wires within any plastic pipes to prevent this (see siliconchip.au/ link/ac71). Major dust producers include circular saws, thicknessers and routers. Where there is more than one appliance, you would typically have a single vacuum unit, with ducting between 54 Silicon Chip them. A valve in the ducting at each appliance, called a ‘blast gate’, can be opened or closed for the vacuum to draw dust only from the appliance concerned (otherwise, the suction would be too weak). With our Vacuum Controller, the operation of the vacuum and blast gates is fully automatic. Switch on your appliance, and the vacuum will automatically start and run for as long as the appliance is running. Then, once the appliance is switched off, the vacuum will continue to run for a preset period. Blast gate control can be automated provided the blast gates are electrically operated by actuators or solenoids. Solenoids use an electromagnet that pulls in a plunger whenever the solenoid is powered. A spring is used to return the plunger to its resting position when power is off. An actuator is essentially a DC electric motor that drives a rod out or in using a worm gear. If you are not familiar with actuators, you can see an example of one at siliconchip.au/link/ac72 When used with the Vacuum Controller, the blast gate associated with the powered on appliance is opened. The appliance or appliances that are not operating will have their blast gates closed. Australia's electronics magazine A woodworking workshop setup for removing dust is not a topic that we will investigate in detail here. There is much detailed information on it at siliconchip.au/link/ac73 and other reputable websites on the topic. Presentation Our Vacuum Controller can be built to suit your workshop. Its most basic form is a single Vacuum Controller unit that switches a vacuum for a single appliance. The Vacuum Controller detects when its appliance is running and powers the vacuum. We call this Vacuum Controller the master unit. It is the only unit that contains the switching components for the vacuum. The optional blast gate control can be connected to this unit. This provides relay contacts to enable control of a solenoid or actuator to open or close the blast gate. It is connected via an 8P8C RJ-45 connector that allows standard Cat 5/Cat 6 leads to be used. You can use a different connector should more current be required (more on that later). For each appliance after the first, you will need another partially populated Vacuum Controller board. These extra units don’t include the switching components for the vacuum, as they are connected back to the main unit. This interlinking allows any of the siliconchip.com.au Appliance & vacuum ratings: up to 10A at 230V AC Appliance on-detection threshold: 166mA (~40W) Vacuum run time after appliance is off: adjustable from half a second to 30s Blast gate opening and closing time compensation: 0-7.5s Vacuum wind-down period compensation: 0-7.5s Can be used with a single appliance or multiple appliances via interlink connections Optional blast gate control option for each appliance; it opens for the appliance being used Cat 5/6 or telephone cables for interlinking & blast gate control Fully automatic operation plus manual operation for vacuum and blast gate Power, vacuum and blast gate indicators troller interconnected Vacuum Controllers to control the action of the vacuum via the master unit. When a Vacuum Controller unit detects that its connected appliance is on, the master unit is signalled to switch on the vacuum. If using blast gates, there are two possible control methods that can be selected. The default is to only open the blast gate for the currently operating appliance. The other option will keep the blast gate open for the last used appliance. This gate will close when a different appliance starts. Fig.1 shows, as an example, the arrangement of three interlinked units. Interconnection is via RJ-10 4P4C sockets and 4-wire telephone style cabling with RJ-10 plugs for an easy interconnection system. For Home workshops The master unit includes two mains inputs and two mains outlets (General Purpose Outlets [GPO]). These are to supply the appliance and the vacuum independently. Each mains input must plug into a separate mains outlet to allow for up to 10A <at> 230V AC (2300VA) to be drawn from each. Circular saws can be rated at 1800VA or more and vacuums at around 1200VA, so it is not feasible to run both from the one 10A mains outlet. The mains supply for the appliance is directly connected between the input and output via a current transformer inside the Vacuum Controller unit. This current transformer is used to monitor the appliance current. When current is detected, it indicates to the Vacuum Controller that the appliance is running and so switches on the vacuum via the second mains output. Power for the vacuum is switched using a heavy duty relay. If more than one Vacuum Controller is built, subsequent units only require one mains power input and one mains outlet for that unit’s connected appliance. The vacuum is only switched on and off via the master unit, which is signalled to switch via the interlinking connection between units. If blast gate control is installed, interlinking sets the blast gate open for the appliance that is running and closes the blast gates for those units that do not have their associated appliance running. There is the option to have the blast gate for the last running appliance kept open after the appliance is switched off. This speeds up switching on the Left: the Blast Gate Control Adaptor is a simple PCB that can be built to convert RJ-45 8P8C (eight position/eight conductor) connections to screw terminals. Right: the Vacuum Pump Controller has two 230V 10A power outlets for supplying the appliance and vacuum. siliconchip.com.au Australia's electronics magazine October 2025  55 vacuum if you use the same tool again. When the blast gate is closed, it needs to wait for the blast gate to open before the vacuum is started. If the blast gate is already open, the vacuum can start immediately. LED indicators are included on each for power, vacuum running and blast gate open. Two momentary pushbutton switches provide manual control of the vacuum and the blast gate. The blast gate LED, associated switch and other blast gate related components can be left off if you don’t need this feature. Also, the interlinking components are not necessary if you only intend to build one master unit. One or two additional units can be connected to the master unit and be powered from it. The master unit has a mains transformer to power itself, and the resulting 12V is supplied to other units via the interlink connections. If more than three units are required, then the fourth unit will need to include another power transformer. This allows for up to six to be connected in total. Because the Vacuum Controller can be built with several options, the circuit and PCB overlay diagrams show the separate sections of the circuit, some of which may not be required in each unit. Similarly, the parts list separates out the parts for each section. Timers and operation Three timers are used in the operating logic: the vacuum timer, blast gate operating period timer and the vacuum wind-down timer. The vacuum timer sets the period for which the vacuum runs after the appliance is switched off. This can 56 Silicon Chip be adjusted from 0-30s. The blast gate timer should be set to the time taken for the blast gate to open or close, allowing the blast gate to be fully open before the vacuum is started. It prevents damage to the vacuum pipe work and blast gates if all blast gates are closed when the vacuum starts. The blast gate timeout can be set up to 7.5s. If blast gate control is not used, it can be set to zero, for no delay in starting. The vacuum wind-down timer is included so that the blast gate does not close until the vacuum motor has stopped after being switched off. It can be set for up to 7.5s, preventing excessive vacuum pressure by keeping the blast gate open while the vacuum is spinning down due to inertia. The Vacuum Controller is initially in a waiting state until either its connected appliance is switched on, or the interlink signal indicates that the appliance connected to another unit is switched on. As long as neither are on, it continues to wait. When the connected appliance switches on, the blast gate is powered on if it isn’t already open. The blast gate LED flashes during the opening period (this is skipped if it was already open). The interlink signal then becomes active. At the same time, the vacuum motor and its indicator LED are switched on. After the appliance is switched off, the vacuum timer starts. When it ends, the vacuum is switched off, along with the interlink signal. If JP1 is in, the vacuum LED flashes during the pump wind-down period. In this case, after the wind down period, the blast gate closes and its Australia's electronics magazine LED goes off. If JP1 is out, the blast gate and LED stay on, and the vacuum wind-down period is bypassed. Either way, it then goes back to the initial state, checking for the appliance or interlink signal to become active. If, rather than the connected appliance switching on, the interlink signal becomes active, all units other than the one with the connected appliance on will have their blast gate closed, if not closed already. The blast gate LED flashes during the closing period. Then the blast gate LED switches off. The vacuum and LED then switch on, and stay on as long as the interlink signal remains active. When the interlink signal goes off, the vacuum motor is switched off. It then returns to the initial waiting state. Note that the state of the blast gate is stored in non-volatile memory, so the on/off setting for each blast gate is restored on power-up. This does not apply to when the blast gate was set open manually via button S2. Switching the vacuum on manually using switch S1 will cause the master unit to switch on the vacuum. The vacuum LED on the unit where S1 was pressed will light but flash off momentarily once per second to indicate manual mode. Automatic running by interlink signal or appliance detection is disabled until the vacuum is switched off via S1 on the unit that initiated manual operation. Manually opening the blast gate on any unit does not affect automatic operation. When an appliance switch-on is detected by one of the units, the blast gates will be closed for all units that did not detect an appliance-on, and remain open or be siliconchip.com.au Fig.1: one control unit is required for each tool that’s connected to the vacuum system. Two, three or even more units can be linked together, as shown here. Only the first unit connects to the vacuum, and just the first (and the fourth, if there are four to six) requires the second mains input. In use, apply power to the fourth unit (ie. the second mains input unit) before the first unit. The blast gate connections are only required if you’re using a blast gate system. opened at the unit that detected the appliance-on event. Note that the timer periods are determined by the Controller that has detected the appliance that’s switched on. If it is not the master unit, the vacuum run period is controlled via the interlink signal from another unit. This allows you to set different periods for each tool. Circuit details The circuit is shown in Fig.2. It is in several sections; if you don’t want blast gate control, that part of the circuit can be left off the PCB. Similarly, if you just have a single tool to connect, the interlinking section can be left out. When a second or third unit is built, they do not require the mains power section to be populated. They can instead receive 12V power from the master unit. More than three units can be joined, but one mains power supply is required for every three. Power is interconnected using CON7 and CON8 via jumpers at JP2 and JP3. If more than three units are connected, the supply must be broken between the third and fourth unit by leaving JP2 or JP3 out. The master Vacuum Controller is the only unit that requires the vacuum control section, comprising relay RLY1, driving transistor Q1, diode D1, the 1kW base resistor for Q1, the mains power input and output connectors (CON13/CON14) and fuse F2. The Vacuum Controller is based around microcontroller IC1. This monitors the appliance current flow, trimpot settings (VR1, VR2 & VR3), switches S1 and S2, jumper selection JP1 and the interlinking signal. It also drives relays RLY1 & RLY2 for vacuum and blast gate control, LED2 and LED3, and the interlinking signal. RLY1 and RLY2 are switched on by the RC4 and RB7 outputs of IC1, respectively. Both use 1kW current-­ limiting series base resistors to drive transistors Q1 and Q2. When a transistor is switched on, its collector goes low, connecting one side of the relay coil to ground. The 12V supply at the other end of the coil powers the relay. Diode D1 across RLY1’s coil, and diode D2 for RLY2, quench the backEMF voltage from the coil when these are switched off. RLY1 is a single-pole, single-throw (SPST) relay with 30A, 250V AC contacts to drive the vacuum. Mains active from the vacuum IEC C14 mains input power connector (CON13) is controlled via the relay contact to switch mains outlet (CON14) power on or off. RLY2, for blast gate control, is a 5A double-pole, double-throw (DPDT) relay. All its relay contacts are connected to screw terminals (CON5) and to CON6, an RJ-45 connector. This allows for an easy connection using Cat 5 or Cat 6 cabling. A small adaptor PCB can be used to convert the RJ-45 connections to 6-way screw terminals at the other end, for wiring to the solenoid or actuator. Current detection Appliance current flow detection is via the Active mains wiring between the appliance input (CON11) and output (CON12); the Active wire passes through current transformer T2. This forms the primary winding for the current transformer. T2 produces an output current from its secondary winding that’s related to the current flow through the mains Active wire. The lid (shown left) requires holes for the three LED indicators and the manual control switches. We have used fibre optic cable to transmit the light, as the LEDs are mounted to the PCB. siliconchip.com.au Australia's electronics magazine October 2025  57 The 10kW loading resistor gives about 4V AC output with a tool current flow of 1A and the single pass of the Active mains wire through the current transformer core. While the input current to output voltage for T2 is not very linear using a 10kW loading resistance, we use this high value to increase the sensitivity. A 100W loading resistor would be used for measuring current more accurately. That would provide a more linear relationship, but sensitivity would be reduced to only give 1V for a 10A primary current with a single turn through the transformer. Since we are not interested in current reading accuracy, we use the higher-­sensitivity connection to detect the appliance running current. The startup current for the appliance can be well over 20A, so the output voltage from the current transformer could be quite high (possibly around 80V). We limit this voltage using a transient voltage suppressor (TVS1) that clamps the voltage to about 13.8V AC. This limits the current into the following op amp inputs to a safe level. Voltage rectification The output from T2 needs to be rectified to give a DC voltage suitable for monitoring by microcontroller IC1. A standard bridge rectifier requires a signal greater than ±1.2V peak to begin producing a rectified voltage. Fig.3: the Blast Gate Adaptor circuit (top) and wiring to use for a blast gate with an actuator (bottom). With power applied with the polarity shown, the blast gate should close. You can test this by switching on the 12V supply with the controller off; if the blast gate opens, reverse the connections. 58 Silicon Chip A precision full-wave rectifier allows the detection of voltage well below this (down to a millivolt or less). The rectification is done purely by op amps (IC2a and IC2b), without the aid of diodes. We have set the gain of this precision rectifier to 1.5 times. Rectifying the incoming AC voltage without diodes is possible, provided that the op amp has specific characteristics. These include being able to operate correctly (without output phase reversal) when a voltage is applied that’s below its ground supply rail. In addition, the op amp must be able to pull its output close to ground. If you are interested in how this works in detail, this is described in the section entitled “Precision full-wave rectification”. A 2.2kW resistor and 10μF capacitor filter the rectified waveform at the output of IC2a to produce a smoothed DC voltage suitable for IC1 to monitor via its AN6 analog input and internal analog-to-digital converter (ADC). Trimpots VR1 to VR3 are used to set time periods. VR1 sets the period over which the vacuum runs after an appliance is switched off. The voltage at VR1’s wiper determines the time period, and can be set between 0V and 5V. This voltage is converted to a digital value within IC1 using the AN7 analog input that connects VR1’s wiper to the ADC. The VR1 setting gives a time period ranging from about 0.5s when rotated fully anti-clockwise through to 30s when rotated fully clockwise. Similarly, VR2 and VR3 can be adjusted in voltage, but these settings provide time period settings of 0-7.5 seconds. VR2 is the blast gate operation period (the time it takes the blast gate to open or close fully). This determines when the vacuum starts after detecting the appliance associated with the blast gate starts up. VR3 is for setting the vacuum wind down period, the time the vacuum takes to stop after being switched off. We keep the blast gate open until the vacuum has stopped running, whereupon the gate closes. There is an option to keep this gate open when the appliance and vacuum stops and, in this case, the wind down period can be set to 0 (VR3 fully anti-clockwise). The blast gate will close automatically when a different appliance runs if there are more appliances and Vacuum Controllers all interlinked. Australia's electronics magazine Switches S1 and S2 are momentary pushbutton switches connected to the RA5 and RA4 digital inputs of IC1. With the switches open, these inputs on IC1 are pulled high via internal pull-up currents. When a switch is pressed, it pulls the input pin low, close to 0V. Blast gate wiring The connection for a solenoid is easy enough, with the common and normally (NO) contacts used to switch power to the solenoid when the relay is energised. Fig.3 shows how wiring is made for an actuator. An actuator is essentially a DC electric motor that drives a rod in or out using a worm gear. The actuator requires current flow in one direction to open the actuator, by driving the motor in one direction, and current flow in the opposite direction, reversing the motor, to close the actuator. Operating the actuator is achieved using the DPDT relay contacts. The actuator includes end-stop switches that prevent the actuator from running once it has reached its open or closed limits. It is important when used with our Vacuum Controller to wire the actuator so that it opens the blast gate when the relay is on, and closes the blast gate when the relay is off. Power supply Power for the circuit is derived by a mains transformer. This is connected to the appliance power input IEC C14 connector (CON11) and fuse F1 via terminals CON1 & CON2. Transformer T1 has two 9V AC outputs that are connected in parallel. The output is rectified by bridge rectifier BR1 and filtered with two 470μF capacitors to produce around 12V, which powers the two relays. The 12V is also applied to REG1, a 5V regulator, to supply IC1 and IC2. The transformer can deliver enough current to run three of these circuits. Only the master unit has the vacuum control section, hence RLY1, so only one such relay needs to be powered. RLY2 (if used) for blast gate control is only switched on in one of the Vacuum Controller units at a time. Since the relays are the major current draw, there isn’t much of an extra burden when more units are attached. The 12V power for the following units is coupled via the interlinking cable and JP2 (for CON7) or JP3 (for siliconchip.com.au Fig.2: the circuit mainly comprises microcontroller IC1, a currentsensing system comprising current transformer T2 and op amp IC2 (cyan dashed box), a basic mains power supply (red dashed box), vacuum switching (mauve dashed box), blast gate switching (dark blue dashed box) and interlinking components (green dashed box). CON8). For the connection between the third and fourth unit, where the fourth unit has another mains power supply, at least one of the power jumpers between these two units must be left off to isolate the two separate 12V supplies. Interlinking Transistor Q3 provides the interlinking feature. This transistor is driven at its base via a 10kW resistor by IC1’s RB5 output. When RB5 is taken high, the transistor switches on, pulling siliconchip.com.au its collector low. With the transistor off, the collector is held high via the 10kW pullup resistor. The collector voltage is the interlinking voltage. Any transistor in any of the interconnected Vacuum Controller units can pull this line low to indicate that their appliance is running. When no transistors are on, then the interlink signal is held high (5V) via the 10kW resistor and any other 10kW resistors in other interconnected units. Australia's electronics magazine In the unlikely event that more than 10 separate Vacuum Controller units are interconnected, these resistors should be increased in value, or some left off, to keep the total parallel resistance at 1kW or higher. When a unit detects its connected appliance is on, it opens the connected October 2025  59 blast gate. The low interlinking signal causes the remaining blast gates associated with the remaining appliances to be closed. This low interlink signal will also indicate to the master unit that the vacuum should run. The units are interlinked using the RJ-10 4P4C socket (or sockets) at CON7 and CON8. The first (master) and last unit require one of these, while the others all require both. Construction options Fig.4 shows the parts layout on the main board. It is divided into the same sections as the circuit diagrams, with dashed boxes in corresponding colours, since not all components are necessarily required. The ‘core’ components outside these boxes are required for all builds. For the master unit, the mains power (red) and vacuum control (mauve) sections are also required. To use the blast gate option, the components in the dark blue box are also required. Typically, CON6 is used so that connection to the blast gate can be made using a Cat 5 or Cat 6 cable, suitable for handling up to 1A. If you require more current, up to 5A, use the CON5 screw terminals instead, along with suitably rated wiring, passing through a cable gland in the case. For secondary units, the mains power section (red) isn’t required unless you’re building more than three units. Essentially, you’ll need to build this section on every fourth unit. Interlinking between units requires only one RJ-10 socket (CON7 or CON8) on the master or final unit. All others (assuming there are more than two) require both sockets. JP2 and JP3 are used to connect the +12V power as required. Construction The Vacuum Controller unit is built on a double-sided, plated-through PCB coded 10109251 that measures 151 × 109mm. Most of the components are installed on this PCB, and it is housed within an IP65 enclosure measuring 171 × 121 × 55mm. We’ll describe construction assuming everything is installed, so ignore any components that are mentioned if they don’t apply to your build. Start by fitting the resistors. These have colourcoded bands, shown in the parts list, but you should also use a digital multimeter to check each resistor before mounting it. Diodes D1 and D2 are next on the list. Make sure these are orientated correctly before soldering their leads. BR1 can be installed, again with the correct polarity, lining up the + printed on it with the one on the PCB. We used a socket for IC1, although it could be soldered directly, assuming it has already been programmed. Similarly, IC2 can be mounted on a socket or directly onto the PCB. Install the headers for JP1, JP2 and JP3 next. Follow with the capacitors. There are two types used: electrolytic and MKT polyester. The electrolytic capacitors need to be orientated correctly since they are polarised, with their longer leads through the holes marked with + symbols. The MKT polyester capacitors can be installed either way around. REG1 mounts horizontally. Bend its leads to suit the PCB holes and secure its tab with an M3 screw and nut before soldering the leads. Q1-Q3 can then be fitted; they are all the same type; orientate them as shown in Fig.4. CON1 to CON4 can now be installed. Note that the wire entry for CON3 is toward REG1; for CON4, the entry is toward the lower edge of the PCB. Then fit CON5-CON8. CON5 isn’t needed if you intend to use CON6 instead. CON5 allows for heavier-duty wiring to the blast gate. The cable will need to be secured to the side of the enclosure with a cable gland, or via circular (8-way) audio connectors or similar. Fig.4: follow this overlay diagram to assemble each control board, but note that some boards may not require the parts inside each outlined section (for example, the second and third control boards in a system don’t require the mains power supply). The colour coding of the dashed sections corresponds to the same sections in the circuit diagram, Fig.2. 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Precision Full-Wave Rectification We use a dual op amp to rectify the AC signal from the current transformer, either an LMC6482AIN or MCP6272 (IC2). One stage (IC2b) is connected as a unity gain-buffer, while the other (IC2a) provides the 1.5 times gain. The points labelled A to E in Fig.2 correspond to the example waveforms shown here in Fig.a. We’ll describe the operation using a 2V peak-to-peak sinewave at point ‘A’. This makes the description easier since the sinewave peaks at +1V and −1V. The rectification for the negative and positive waveforms are described separately. For the negative half of the cycle, the signal applied to the non-inverting pin 5 input of IC2b via the 15kW resistor will cause the voltage at that pin (point B) to be clamped at around -0.3V due to IC2b’s internal input protection diode. The output of IC2b (point C) therefore sits at 0V during negative portions of the cycle, since its output can’t go below the negative supply rail (0V). IC2a adjusts its output (point E) so that the voltage at its inverting input pin 2 (point D) matches the voltage at non-inverting input pin 3 (point C). Since pin 3 is at 0V, pin 2 will also be at 0V. Therefore, the 10kW resistor from point D to ground has no voltage across it, and it plays no part in the circuit during the negative portions of the cycle. With the 10kW resistor essentially out of the circuit, IC2a operates as a standard inverting amplifier with both inputs (points C and D) at 0V. Its gain is therefore −30kW divided by 20kW, which equals −1.5 times. So the −1V peak waveform is amplified and inverted to produce +1.5V peak at point E. With a positive voltage at the input (point A), the situation is more complicated. Firstly, the voltage at pin 5 (point B) is reduced below 1V peak due to the divider formed by the 15kW and 18kW resistors. So the peak voltage becomes 0.5454V, ie, 1V × 18kW ÷ (15kW + 18kW). Point C will also peak at 0.5454V, since IC2b is working as a unity-­ gain buffer producing the same voltage at its output as its non-­ inverting input. Once again, op amp IC2a adjusts the output voltage (point E) so that the voltage at the inverting input at pin 2 (point D) matches the voltage at the non-inverting input, pin 3 (point C). To determine the resulting voltage, we calculate the currents through the three resistors connected to point D. The current through the 10kW resistor is waveform D voltage divided by 10kW, which peaks at 54.54μA (0.5454V ÷ 10kW). The current through the 20kW resistor, with 1V peak at the input (point A), will be 22.73μA, ie, (1V[A] − 0.5454V[D]) ÷ 20kW. So we have 22.73μA flowing into the node at point D via the 20kW resistor and 54.54μA flowing away from that node via the 10kW resistor. The extra current of 31.81μA (54.54μA − 22.73μA) to balance currents at node D needs to come via the 30kW resistor. Remembering that voltage at point D peaks at 0.5454V, the required voltage at point E is 1.5V, ie, 31.81μA × 30kW + 0.5454V. So the circuit operates as a full-wave rectifier with a gain of 1.5. The degree of precision depends on the op amp parameters and resistor tolerances. The lower the offset voltage of the op amp and the lower the op amp input bias current, the more accurate the full-wave rectification will be, particularly at low signal levels. We are not overly concerned with accuracy here. We just need full-wave rectification of the incoming AC signal from the current transformer that works down into the tens of millivolts range. A standard diode-based rectifier would not give any output in this case, due to the relatively large voltage drops across the diodes. The scope output shows the operation of the full-wave rectifier for a 1V peak (2V peak-to-peak) current waveform resulting from an approximate 40W load through the appliance and current transformer. The waveform applied to the input of the full-wave rectifier (point A) is on channel 1 of the oscilloscope, shown in yellow. Channel 2’s cyan waveform is the full-wave rectified waveform (measured at point E). This is a 1.48V peak output waveform at 100Hz compared to 1V peak at 50Hz for the input sinewave. The discrepancy of 20mV is due to tolerances in the resistors that are only ±1% types, the op amp offset voltages, and the accuracy of the oscilloscope readings. The yellow trace is a 1V peak sinewave applied to point A in the circuit (the input of the precision rectifier), while the cyan trace is the output of the rectifier at point E. As expected, the negative parts of the sinewave are flipped to be positive, allowing us to easily measure the average current. Fig.a: the expected waveforms at points A-E on the circuit (Fig.2) for a 1V peak sinewave from current transformer T2. The output (E) is a rectified version of the input (A) but 50% higher in amplitude. siliconchip.com.au Australia's electronics magazine October 2025  61 The next step is to install the relay, RLY1, with the coil terminals toward CON3. The relay is secured using M4 machine screws and nuts, with each screw inserted from the underside of the PCB. RLY2 mounts directly on the PCB. Transformer T1 is a PCB-mounting type; install it now. We use a cable tie that wraps around the transformer and through slots in the PCB to secure the transformer. The cable tie is necessary to prevent the solder joints or pins fracturing if the unit is dropped. Current transformer T2 also needs extra support for its mounting for similar reasons. Apply glue to the transformer base before inserting its pins into the PCB and soldering it in place. We used JB Weld epoxy resin, since this adheres well to most types of plastics. The light pipes are held together over the LEDs when you lose the lid. Blast gate PCB assembly If using blast gate(s) with the RJ-45 socket option, you will probably want Fig.6: the locations of cut-outs on three sides of the case, plus the dimensions of the IEC socket packing piece and the light transporter assembly jig. All the possible holes for chassis-mounting connectors etc are included, although some are optional. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au to build one of the Blast Gate Adaptor PCBs for each gate. This converts the RJ-45 8P8C connections to screw terminals. It is coded 10109252 and measures 44 × 33mm – see Fig.5. This can be mounted near the blast gate actuator or relay. Assembly is simple – just solder the RJ-45 socket and screw terminals to the board and it’s ready. Final assembly The Vacuum Controller units are secured to the base of their enclosures using M3 screws that go into the integral brass inserts. Before attaching the PCB, cutouts are required for the IEC C14 connectors at one end of the enclosure and the RJ-45 and RJ-10 socket(s) at the other end. The only hole that’s required in every case is the IEC C14 connector for the tool or appliance and its corresponding GPO cut-out; the other holes are required only for those boards where matching parts are fitted. Start by drilling and shaping holes using the template shown in Figs.6 & 7. The two IEC C14 connectors used on the master unit have a shared mounting hole at the middle of the enclosure end, where one connector is stacked over the other. The large cutouts for the mains GPO and IEC C14 connectors can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece and filing the job to a smooth finish. Alternatively, use a speed bore drill to remove the bulk of the central cut-out area before filing it to shape. For the master unit, a packing piece needs to be fashioned so that the IEC C14 connector that’s stacked over the other can be spaced by the same amount. We made ours from a piece of 3mm-thick plastic cut from a discarded black UB1 Jiffy box. Once the drilling and filing is complete, the PCB can then be placed inside the case and secured with the M3 screws into the integral brass inserts. The IEC C14 connector(s) must be secured using 15mm-long M3 nylon screws, although metal nuts can be used. For the securing screws closest to the edge of the enclosure, TO-220 insulating bushes can be used to space the nut further out to avoid the nut from angling inward against the enclosure’s moulded curvature as it is tightened. siliconchip.com.au Fig.7: just five holes are required in the lid, as shown in this actual-size diagram. You won’t need all five if you aren’t using the blast gate control option. Using nylon screws prevents the possibility of the screws becoming live (at mains voltage) should a mains wire inside the enclosure come adrift and contact a screw that’s securing the IEC connector. The lid requires holes for the switches and LED bezels of the light transporters. Light transporters use fibre-optic cable and plug-in connectors from the LED to the front panel bezels. The fibre optic cables are cut to length so that they connect without bending too much when the lid is closed. This procedure can be done at the end of construction. Australia's electronics magazine Fig.5: the Blast Gate Adaptor PCB is dead simple; it just connects six of the Cat 5/6 cable’s eight conductors to screw terminals so they can be more easily wired up to the blast gate. This is suitable for gates that draw up to 1A. October 2025  63 Fig.8: the two versions of the lid panel artwork cater for units built with and without the blast gate option. There are also some side labels for connectors that you might like to use. siliconchip.com.au Fig.9: make sure to follow this wiring diagram carefully and only use mains-rated wire. Don’t leave out the cable ties; they are not just to keep it neat; they perform an important safety function (preventing loose wires from contacting low-voltage circuitry). It will be easier to install the lid and attach the light transporters if a plastic spacer is made to spread the LED connector clips 12.5mm apart. We made ours from a 3mm-thick piece cut from a discarded UB1 Jiffy box lid. When installing the lid (later on), it will be easier to make sure the light transporters correctly line up and clip over the LEDs when these are switched on (via S1 and S2 if used) so you can peep in through between the box and lid as you close it. There are two versions of the front panel label artwork, depending on whether the blast gate feature is used or not. Labels for the mains inputs and outputs and the interlinking and blast gate connectors can be independently affixed to the side of the enclosure, or on the side edge of the siliconchip.com.au lid as appropriate. The front panel label shown in Fig.8 is available from siliconchip.au/Shop/11/3002 Details on making a front panel from this artwork can be found online at siliconchip.au/Help/FrontPanels Wiring it up All wiring must be run as shown in Fig.9, using mains-rated cable. Be sure to use 10A cable where indicated (for everything except RLY1’s coil and switches S1 & S2). Brown wire is used for Active, and blue wire for the Neutral leads. The green/yellow-striped wire must be used for the Earth wiring only, and the Earth lead from each IEC connector must go straight to the corresponding GPO. Insulate all the exposed connections with heatshrink tubing for safety, and Australia's electronics magazine cable tie the wires to prevent any wire breakages coming adrift. The Active and Neutral leads are secured to the GPO using a cable tie passing through the hole in its moulding. Use neutral-cure silicone sealant (eg, Roof & Gutter Silicone) to cover the Active bus piece at the rear of the IEC connectors that joins the active pin to the fuse. Take great care when making the connections to the mains socket (GPO), ensuring you run the leads to their correct terminals; each GPO will be marked A (or L) for Active or Live, N for Neutral and E for Earth. Do the screws up tightly so that the leads are held securely. Similarly, make sure that the leads to the CON1 and CON2 screw terminals are firmly secured. CON1 and CON2 are only required October 2025  65 when the transformer (T1) is installed. These screw terminals are there to connect the incoming mains to the transformer primary windings on the PCB. Only one terminal of CON1 is used to connect the Neutral. Similarly, one terminal of CON2 is used for the Active connection. Remove the spare terminal screw on each terminal and use a mica washer (normally used to insulate TO-220 transistors) as a cover for the used terminal. Secure it using an M3 × 12mm nylon or polycarbonate screw with a 6.3mm nylon tapped standoff under the washer through the hole where you removed the metal screw. Setting it up If IC1 is already programmed, it can be inserted into its socket now, taking care to do so with the correct orientation. If IC1 is not yet programmed, do that first. Programmed processors can be ordered from our Online Shop. If you have programming facilities, like a PICkit and adaptor socket, the HEX file is at siliconchip.au/Shop/6/3013 Set VR1 to the required vacuum run time for after the appliance has been switched off. The maximum is 30 seconds in the fully clockwise position. It’s linear, so a halfway setting will give you 15 seconds. Set VR2 to the period that the blast gate takes to open or close, or fully anti-clockwise if you aren’t using that feature. If the blast gate opening and closing periods are different, set it to whichever is longer. The setting is 7.5 seconds when VR2 is fully clockwise. Adjust VR3 for the wind-down period that the vacuum takes to stop after being switched off. As with VR2, it will give 7.5 seconds when VR3 is fully clockwise, or 3.75s at halfway. When you have more than one unit, the VR1, VR2 and VR3 settings are used from whichever control unit that detects the appliance switching on, so you will need to set them all. Indicator LEDs The indicator LEDs will be either flash, be fully on or off. The Power LED is on when power is supplied to the circuit. During the blast gate opening/closing period, the blast gate LED flashes and it remains lit while the blast gate is open, switching off when it closes. The vacuum LED is continuously lit while the vacuum is running on 66 Silicon Chip Parts List – Vacuum Controller Controller unit (common parts) 1 double-sided, plated-through 151 × 109mm PCB coded 10109251 1 171 × 121 × 55mm sealed ABS or PC enclosure [Altronics H0478, Jaycar HB6218] 1 AC1010 or AX1000 10A current transformer (T2) [RS Components 7754928, 1243903] 1 3-way, 5.08mm-pitch screw terminal block (CON4) 1 M205 10A fast blow fuse (F1) 1 2-way, 2.54mm-pitch pin header and jumper shunt (JP1) 1 SPST momentary pushbutton switch (S1) [Altronics S1084A, Jaycar SP0700] 1 IEC C14 mains input socket with fuse holder (CON11) [Altronics P8324, Jaycar PP4004] 1 side-entry 10A mains GPO socket (CON12) [Altronics P8241, Jaycar PS4094] 3 3mm LED light transporters [Jaycar HP1193; pack of 3] 1 LED fibre optic spreader made from 3mm plastic (see Fig.6 and text) 3 10kW miniature top-adjust trimpots (VR1-VR3) 1 20-pin DIL IC socket for IC1 (optional) 1 8-pin DIL IC socket for IC2 (optional) Hardware and cable 1 150mm length of 7.5A mains-rated wire for S1 1 200mm length of blue 10A mains-rated wire 1 250mm length of brown 10A mains-rated wire 1 150mm length of green/yellow striped 10A mains-rated wire 1 40mm length of 5mm diameter blue or black heatshrink tubing 1 40mm length of 5mm diameter red or black heatshrink tubing 1 40mm length of 5mm diameter green heatshrink tubing 1 40mm length of 3mm diameter blue or black heatshrink tubing 1 40mm length of 3mm diameter red or black heatshrink tubing 2 M3 × 15mm nylon countersunk head screws 4 M3 × 6mm panhead screws 2 M3 hex nuts 1 TO-220 insulating bush 4 100mm-long cable ties Semiconductors 1 PIC16F1459-I/P 8-bit microcontroller programmed with 1010925A.HEX, DIP-20 (IC1) 1 LMC6482AIN or MCP6272E/P dual CMOS op amp, DIP-8 (IC2) [Jaycar ZL3482] 1 7805 5V 1A linear regulator, TO-220 (REG1) 2 3mm red LEDs (LED1, LED2) 1 (P)4KE15CA 15V bidirectional TVS (TVS1) [Jaycar ZR1160] Capacitors 1 470μF 16V PC electrolytic 2 10μF 16V PC electrolytic 1 100μF 16V PC electrolytic 2 100nF 63V or 100V MKT polyester Resistors (all ¼W, 1% axial) 1 30kW 1 18kW 4 10kW 2 470W 1 20kW 1 15kW 1 2.2kW Mains power supply parts 1 9 + 9V AC 3VA PCB-mounting mains transformer (T1) [Altronics M7018A] 2 PCB-mounting 8.25mm-pitch 300V 15A barrier screw terminals (CON1, CON2) [Altronics P2101] 1 W04 bridge rectifier (BR1) 1 470μF 16V PC electrolytic capacitor 2 M3 × 12mm nylon or polycarbonate panhead machine screws 2 M3 × 6.3mm nylon tapped spacers 2 TO-220 mica insulating washers 1 150mm-long cable tie Extra parts for master unit (besides mains power supply) 1 SPST 250V/30A 12V DC coil FRA4 relay (RLY1) [Jaycar SY4040] 1 2-way, 5.08mm-pitch screw terminal block (CON3) 1 IEC C14 mains socket with integral fuse holder (CON13) [Altronics P8324, Jaycar PP4004] 1 side-entry 10A mains GPO socket (CON14) [Altronics P8241, Jaycar PS4094] 1 M205 10A fast blow fuse (F2) 1 BC337 45V 0.8A NPN transistor (Q1) Australia's electronics magazine siliconchip.com.au 1 1N4004 1A diode (D1) 1 1kW ¼W 1% axial resistor 1 200mm length of 7.5A mains-rated wire for the relay coil 1 200mm length of blue 10A mains-rated wire 1 250mm length of brown 10A mains-rated wire 1 150mm length of green/yellow 10A mains-rated wire 1 M3 × 15mm nylon panhead machine screw 1 M3 hex nut 1 TO-220 insulating bush 1 IEC mounting spacer made from 3mm-thick plastic (see Fig.6 and text) 11 100mm-long cable ties Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Extra parts for blast gate control (per unit) 1 DPDT 5A PCB-mounting relay (RLY2) [Altronics S4190D, Jaycar SY4052] 1 SPST momentary pushbutton switch (S2) [Altronics S1084A, Jaycar SP0700] 1 RJ-45 8P8C side-entry PCB-mounting socket (CON6) [Altronics P1448A] • 1 BC337 45V 0.8A NPN transistor (Q2) 1 3mm red LED (LED3) 1 1N4004 400V 1A diode (D2) 1 1kW ¼W 1% axial resistor 1 470W ¼W 1% axial resistor 1 Cat 5 or Cat 6 cable (not crossover), length to suit installation • 1 Blast Gate Adaptor (see below) • 1 150mm length of 7.5A mains-rated wire for S2 2 100mm-long cable ties • or replace these parts with 2 3-way, 5.08mm-pitch terminal blocks (CON5) and a cable gland or chassis connector plus wiring to the blast gate for >1A Interlinking two or more controller units (per pair of units) 1-2 RJ-10 4P4C side-entry PCB-mounting sockets (CON7, CON8) [Altronics P1442] 1-2 2-way, 2.54mm-pitch headers and jumper shunts (JP2, JP3) 1 4P4C handset (telephone) cord with RJ-10 connectors at each end; length to suit 1 BC337 45V 0.8A NPN transistor (Q3) 1 10kW ¼W 1% axial resistor Blast Gate Adaptor (per adaptor) 1 double-sided, plated-through PCB coded 10109252, 44 × 33mm 2 3-way, 5.08mm-pitch screw terminal block (CON9) 1 RJ-45 8P8C side-entry PCB-mounting socket (CON10) [Altronics P1448A] Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of Silicon Chip. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. all units when powered, but flashes on and off with an even duty cycle once per second during the winddown period. This LED also flashes momentarily off at the unit where the vacuum is set to run manually using S1. This indicates that manual mode was used, and the vacuum needs to be switched off using S1 to exit this mode before it resumes automatic operation. Don’t forget to set JP1 in each unit as required. Leaving the jumper link out will have the blast gate stay open after opening. It will only close if another Vacuum Controller unit detects its appliance is on instead. With the jumper link in, the blast gate will close after the vacuum has SC stopped running. siliconchip.com.au Australia's electronics magazine October 2025  67