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Remote-Controlled Mains Switch Want to switch mains appliances on and off remotely? This UHF Remote Mains Switch can do it for you. It’s operated using a hand-held UHF transmitter or you can team it with the Water Tank Level Meter Base Station described last month to automatically control mains-operated water pumps. An in-built timer also enables the unit to turn off automatically after a preset period. By JOHN CLARKE T The transmitter has two buttons to turn the UHF Remote Mains Switch On and Off. It can control up to 10 switch units simply by changing the identity setting. 24  Silicon Chip HERE ARE MANY INSTANCES when it would be convenient to switch an appliance on or off remotely rather than switching it manually. Such circumstances include switching on pathway lights when you arrive home, switching garden and/or pool lighting on or off, and switching power to water pumps. Remote switching can also be very convenient for appliances that are difficult to access, eg, in a factory. This unit was originally designed to switch mains-powered water pumps on and off in response to signals transmitted by the Water Tank Level Meter Base Station described last month. However, we soon realised that by adding a separate handheld transmitter to control the unit, it could also be used as a stand-alone unit for lots of other applications. It’s quite simple really – if you want to team the unit with the Water Tank Level Meter Base Station, then you don’t need the handheld transmitter. That’s because a transmitter is built into the Base Station itself. Conversely, you do need the transmitter to use the unit in other applications – ie, without the Base Station. siliconchip.com.au The UHF Remote Mains Switch can switch loads of up to 1875W or 2500W – see text. By the way, commercial remote control mains operated switches are readily available for switching appliances rated up to 1000W. Typical of these is the Altronics Cat. A-0340 which can be used with up to five outlets and has a range of 20m. However, if you want to switch devices rated over 1000W or control water pumps, then you need the UHF Remote Mains Switch described here. It can switch devices rated at up to 2500W over a range of up to 200m. That’s 10 times the range typically available from the low-cost commercial units! Main features As previously indicated, the UHF Remote Mains Switch is controlled either via a Water Tank Level Meter Base Station or using a hand-held UHF transmitter. The latter has just two switches for power control, one to switch the appliance on and the other to switch it off. An indicator LED located just above the “On” switch lights briefly during each UHF transmission, to indicate that the signal has been sent. A feature of the transmitter unit siliconchip.com.au is that is can be set to one of 10 identities. This means that you can independently control up to 10 UHF Remote Mains Switches using a single transmitter. Let’s say, for example, that you have two UHF Remote Mains Switches. In this case, one of these can be set as identity “1” and the other as identity “2”. The UHF transmitter can then be set to control either UHF Remote Mains Switch by selecting the required transmitter identity number. In other words, when the transmitter is set to identity “1” it will control the UHF Remote Mains Switch with identity “1”. Similarly, when set to identity “2” it will control the UHF Remote Mains Switch with identity “2”. Note that a small screwdriver is required to change the transmitter’s identity. It’s just a matter of changing the setting of a BCD switch via an access hole in the front panel (below the “On” button). Similarly, the Water Tank Level Meter Base Station transmits the identity of the pump that’s to be controlled. This pump is then switched by the UHF Remote Mains Switch that’s set to the same identity. Note that you will require a separate UHF Remote Mains Switch for each pump you wish to control. Encode switch The transmission range is such that you can easily control a UHF Remote Mains Switch up to 200m away. This means that, in a suburban environment, you could easily end up controlling a neighbour’s UHF Remote Mains Switch or vice versa, unless special precautions are taken. In this unit, a 16-position encode switch is included to prevent this from happening. Basically, the encode setting on the UHF Remote Mains Switch must match the encode setting on the UHF transmitter before it will operate in response to the UHF signal. This means that if both you and a neighbour have UHF Remote Mains Switches set to identity 1, you can simply select a different encode value to prevent false triggering. Timer An inbuilt timer in the UHF Remote Mains Switch allows you set the unit to automatically turn off after a preset period. This period is set by a BCD February 2008  25 Main Features • • Switches loads of up to 1875W (or 2500W using 10A mains wiring). • • • 16 encoder selections. • • On and off switching via remote transmitter or local switch. • • • Brownout detection switching. Up to 10 units can be used with the one transmitter, each with a separate identity. Over 200m range. Unit is operated using a separate handheld UHF transmitter or via a Water Tank Level Meter Base Station. Timer operates from 1 minute to 4 hours in 15 ranges, plus a continuously on selection. Optional power-on variation. Not suitable for security applications. switch during construction and ranges from 1 minute through to 4 hours in 15 steps. Table 2 shows the full range of periods available. This automatic switch-off feature is useful if you are controlling pathway or garden lights. For example, you might want the unit to automatically switch the pathway lights off after a few minutes or switch the garden lights off after a couple of hours. Alternatively, the unit can be set to permanently remain on until an “off” signal is received from the transmitter (ie, either from the hand-held transmitter or from the Base Station transmitter). Brownout protection Another feature of the UHF Remote Mains Switch is “brownout” detection, with automatic switch-off should a brownout occur. Brownouts occur when the mains voltage drops to a lower than normal level, usually because of a fault in the supply. The lowered voltage not only dims house lights but can also cause motors to overheat and burn out. Basically, burn-out occurs because the current through a motor’s induction windings increases when it is not spinning at its correct speed (ie, when the supply voltage is low). In fact, in severe brownouts, the voltage can be so low that the motor will not turn at all. In that situation, the motor will quickly overheat and suffer permanent damage. By including brownout detection, 26  Silicon Chip the motor is protected by switching off the power if the supply voltage falls below a preset value. Brownout detection is vital when it comes to preventing burn-out of mains-powered water pumps. Presentation As shown in the photos, the UHF Remote Mains Switch is housed a plastic enclosure with a General Purpose Outlet (GPO) on the front panel. Also included on the front panel is a neon indicator to indicate when power is applied to the GPO, plus a pushbutton switch to manually switch the unit on and off. Power indication for the unit itself is provided a neon indicator within the mains switch. An internal relay is used to switch the power to the GPO. This relay is a high-current type that’s suited to withstanding the high start-up currents associated with motors. A heavier duty relay can be used if required to power motors rated up to 2500W. The transmitter is housed in a case measuring 135 x 70 x 24mm. It’s powered by a 9V battery and sends out a coded 433MHz signal. Circuit details Fig.1 shows the circuit details for the UHF Remote Mains Switch. It’s based on IC1, a PIC16F88-I/P microcontroller. This monitors the signals from a 433MHz receiver module and controls the GPO via a relay circuit accordingly. In operation, the 433MHz receiver picks up the transmitter signal and applies the resulting data to IC1’s RA5 (pin 4) input via a 1kW current-limiting resistor. This resistor is included because the RA5 input can cause IC1 to latch up if excessive current flows into or out of this pin. This could happen if the input goes above 5V or below the 0V supply rail. The data signal is read by IC1 by clocking it in at a rate set by the transmission locking pulse. It is then accepted by IC1 if the format is correct but will be rejected if its identity and encode values do not match the settings of BCD (binary coded decimal) switches S1 and S2. Switch S1 (identity) is arranged as a rotary switch with 10 settings ranging from 0-9. It connects the RB0, RB1, RB2 and RB3 inputs of IC1 to ground when its 2, 4, 1 & 8 switches are closed respectively. Conversely, the RB0-RB3 inputs are pulled to the +5V supply rail when their corresponding switches are open. That’s because each input has an internal pull-up resistor of about 20kW. In operation, the switch settings for S1 can be read by IC1 because a low voltage on one of the inputs means that its corresponding switch is closed while a high voltage means that the switch is open. BCD switches S2 (encode) & S3 (timer) are monitored in a similar way. However, these have six extra positions labelled A-F, giving a total of 16 positions. Note that the RA0, RA1, RA6 & RA7 inputs of IC1 that monitor S3’s setting are pulled to +5V via external 10kW resistors. These resistors are necessary because there are no internal pull-ups at the RA pins. Switching the relay IC1’s output at RA3 controls relaydriver transistor Q1 via a 330W resistor. When RA3 is high, Q1 switches on and so relay RLY1 also turns on and switches mains power to the GPO (ie, it switches the Active lead). Diode D5 clamps the back-EMF voltage that is produced when the relay coil switches off, to protect the transistor. S4 is used to manually switch the relay on or off with each consecutive pressing. This switch connects to IC1’s RA4 input and pulls this input to ground when closed. Conversely, a 1kW resistor pulls RA4 high when the switch is open. The 100nF capacitor siliconchip.com.au 8 4 2 1 8 4 2 1 11 13 12 10 9 7 6 8 4 5 RA6 RA1 RB7 RB5 RA7 RB6 RA3 RA0 Vss IC1 PIC16F88-I/P AN2 RA4 RB4 RB3 RB1 RB0 RB2 RA5 14 Vdd 15 18 16 17 2 1 3 TPG TP1 4x 10k 100nF 8 4 2 1 COM S3 330 10 F 16V TIMER (0–F) 1k 100nF 1k WARNING: WIRING IN THE SHADED AREA MAY POSE A RISK OF LETHAL SHOCK IF TOUCHED! UHF REMOTE MAINS SWITCH RECEIVER ENCODE (0–F) COM S2 1k F1 10A DATA IDENTITY (0–9) COM S1 GND 433MHz RX MODULE 100 F 16V B D5 A K E C Q1 BC337 RLY 1 +12V NEON LAMP 10 F 16V A K D1–D5: 1N4004 POWER S5 * NOT REQUIRED FOR HEAVY DUTY RELAY (SEE TEXT) 470 * 0.5W S4 ON/OFF A 240V E 100 F 16V 10 F 16V 6.3V B 0V 6.3V C BC337 E GPO T1 2851 IN N A A BROWNOUT LEVEL SET GND OUT REG2 7812 GND IN K 17V K 433MHz Rx MODULE A A GND K K D1–D4 VR1 10k 22k 470 F 25V +17V 100 F 25V +17V S1 78 ➡ 4 C 1 S2, S3 A ➡ BC DE 4 C 1 2 C 8 7805, 7812 OUT IN 2 C 8 Fig.1: the circuit for the UHF Remote Mains Switch is based on a 433MHz receiver module and a PIC16F88-I/P microcontroller (IC1). The microcontroller processes the data from the receiver and controls relay RLY1 which switches the power to the mains socket (GPO) accordingly. SC 2008 N MAINS E INPUT A ANT Vcc 100nF CERAMIC OUT REG1 7805 ANT GND GND Vcc 901 23 +5V 78 9 4 56 456 Vcc DATA DATA GND 23 siliconchip.com.au F0 1 February 2008  27 23 4 56 23 10k 10k 45 23 6 S2 Vcc GND GND ANT DATA Vcc GND DATA 901 1k 4 C 1 ➡ 100nF 100nF BC DE S1 78 9 A D5 4 C 1 ➡ 78 18020101 L ORT N O C P MUP K NAT RETAW ➡ S3 2 C 8 456 78 9 BC DE 330 4 C 1 470 * 100 F 1k CORD GRIP GROMMET 10k 1k TP1 Q1 170mm OF 1mm ENAMELLED COPPER WIRE 10 F 100nF 7.5A MAINS CABLE FOR LOADS UP TO 1875W, 10A CABLE FOR LOADS UP TO 2500W 10k D4 D1 240V PRIMARY LEADS 6.3V 0V 6.3V VR1 10 F A SPADE TERMINAL M4 SCREW RLY1 & NUT 100 F IC1 PIC16F88-I/P SWITCH 1 TPG 10 F 470 F 22k SWITCH 2 REG1 7805 REG2 7812 100 F S5 (N) 2851 NEON 3 (A) F0 1 HEATSHRINK SLEEVING (N) F0 1 F1 T1 (A) 2 C 8 AERA G NIRI W S NIA M 10A TERMINAL BLOCK 433MHz Rx MODULE * NOT NEEDED FOR HEAVY DUTY RELAY NEON LAMP NOTE 2: BEND TOPS OF SPADE CRIMP CONNECTORS ON RELAY OVER SLIGHTLY TO CLEAR CASE LID E A 4.5mm DIAM. NOTE 1: INSULATE TERMINALS OF FUSE F1 & THE NEON LAMP WITH HEATSHRINK SLEEVING N GPO 14 10.9 S4 RADIUS 16.75 NOTE 3: USE THE HEAVY DUTY RELAY FOR LOADS ABOVE 1875W -- SEE PARTS LIST 33.5 (BOX LID) DETAILS OF CUTOUT IN LID FOR GPO Fig.2: follow this parts layout and wiring diagram to build the UHF Remote Mains Switch. Note that all wiring must be run using 240VAC cable (see text) and this must be firmly secured using cable ties as shown in one of the photos. The cutout diagram for the GPO is shown at bottom right. bypasses any glitches that may otherwise cause false switching. Power supply Power for the UHF Remote Mains Switch comes from the mains via transformer T1. The transformer’s 12.6V secondary voltage is then fullwave rectified using diodes D1-D4 28  Silicon Chip and filtered using 470mF and 100mF electrolytic. The resulting 17V DC rail is then applied to 3-terminal regulators REG1 & REG2 to derive regulated +5V and +12V rails. The +5V rail is used to power IC1 and the 433MHz receiver module, while the +12V rail powers the relay. Note that the outputs of REG1 and REG2 are each bypassed using 10mF capacitors. In addition, a 100mF capacitor and two 100nF capacitors are used to further decouple the supply for IC1 and the 433MHz receiver module. Brownout IC1’s AN2 input is used for brownsiliconchip.com.au out detection. Basically, this input samples the 17V rail via a voltage divider consisting of a 22kW resistor and trimpot VR1. VR1’s wiper voltage is filtered using a 10mF capacitor (to smooth out 100Hz ripple and transients) and applied to the AN2 input via a 1kW resistor. During the set-up procedure, VR1 is adjusted so that the voltage at AN2 is +2.5V when the mains voltage is 250VAC. If a brownout subsequently occurs and the mains drops to below about 200VAC, the voltage applied to AN2 will fall below 2V. This is detected by microcontroller IC1 which then switches the relay off to disconnect power from the GPO. The relay subsequently switches on again when the mains supply returns to normal. One small problem with monitoring the 17V rail is that it varies with load. Relay RLY1 has a coil resistance of 160W and so there is an extra 75mA drawn from the 17V rail when the relay is on. As a result, this supply rail drops in level when the relay is on, so we have to take this into consideration. In practice, it’s just a matter of ensuring that trimpot VR1 is set when RLY1 is on and power is being applied to the GPO socket. By doing this, the brownout detection operates correctly when the mains voltage drops to 200VAC. Note also that we have included a 470W resistor across the 160W relay coil and this reduces the effective resistance to 120W. We have done this so that a heavy-duty relay that has a coil resistance of 120W can be used instead without affecting the brownout settings. The 470W resistor is not used with the 120W relay. Another possible problem is that when the relay switches off due to a brownout, the 17V rail immediately rises again due to the reduced load. This could cause the relay to immediately switch on again, only to then switch off again when the 17V rail drops. This cycle could thus go on indefinitely as the AN2 input repeatedly goes above and below 2V, thereby causing relay chatter. To circumvent this relay chatter, the microcontroller doesn’t switch the relay back on again following a brownout until its AN2 input rises above 2.5V, corresponding to a mains voltage of 220VAC. When the relay is switched on, the voltage at AN2 will then fall to 2.2V but this is still 200mV above the voltage required to switch off the relay and so the relay remains on You Need A Ratchet Type Crimping Tool One essential item that’s required to build this project is a ratchetdriven crimping tool, necessary for crimping the insulated quick-connect terminals to the leads. Suitable crimping tools include the Altronics Cat. T-1552, Dick Smith Electronics Cat T-3535 and the Jaycar TH-1829. These all feature doublejaws so that the bared wire end and the lead insu­lation are crimped in a single action. Don’t even think of using one of the cheap (non-ratchet) crimpers that are typically supplied in automotive crimp kits. They are not up to the job for a project like this, as the amount of pressure that’s applied to the crimp connectors will vary all over the place. This will result in unreliable and unsafe connections at the mains switch and relay terminals. By contrast, a ratchet-driven crimp­ i ng tool applies a preset amount of pressure to ensure consistent, reliable connections. If you don’t have a suitable crimping tool, then it will be necessary to solder the leads to the mains switch and relay and cover the connections with heatshrink sleeving. Construction Construction of the UHF Remote Mains Switch is straightforward, with most of the parts installed on a PC board coded 10102081 and measuring 160 x 110mm. The only off-board parts are the GPO socket, pushbutton switch S4, power switch S5, the neon lamp and the fuseholder. Fig.2 shows the parts layout on the PC board. Begin by carefully checking your board for any defects, such as shorted or open-circuit tracks. That done, check that the hole sizes are correct. In particular, the holes for the four corner mounting screws and for REG1 & REG2 must be 3mm in diameter, while the mounting holes for transformer T1 and the relay must be 4mm in diameter. You should also check that the main PC board is cut and shaped to size so that it fits into the box. If not, you can make the corner cut-outs using a hacksaw and a round file. Now for the board assembly. Install the resistors first, taking care to place each in its correct position. Table 1 shows the resistor colour codes but you should also use a digital multimeter to check each resistor before mounting it in position. Note that if you are using the 120W heavy duty relay, then the 470W resistor immediately to its right is not used. Once the resistors are in, install the wire link (it goes in between the two regulators), then install PC stakes for the antenna connection at bottom right and for TP1 and TP GND. In addition, you will need to install another three PC stakes to terminate the transform- Table 1: Resistor Colour Codes o o o o o o siliconchip.com.au No. 1 4 3 1 1 Value 22kW 10kW 1kW 470W 330W 4-Band Code (1%) red red orange brown brown black orange brown brown black red brown yellow violet brown brown orange orange brown brown 5-Band Code (1%) red red black red brown brown black black red brown brown black black brown brown yellow violet black black brown orange orange black black brown February 2008  29 Parts List 1 PC board, code 10102081, 160 x 110mm 1 IP65 ABS enclosure, 171 x 121 x 55mm 1 433MHz UHF data receiver (Jaycar ZW-3102 or equiv.) 1 2851 12.6V 2VA mains transformer 1 12V relay with 20A 220VAC contacts (Jaycar SY04042 or equivalent). Note: for loads above 1875W, use a 30A relay (Jaycar SY-4040 or equivalent) 1 2-way 10A mains terminal block 1 0-9 BCD DIL PC-mount switch (S1) 2 0-F BCD DIL PC-mount switches (S2,S3) 1 momentary push to close 250VAC panel-mount mains switch (S4) (Jaycar SP-0716, Altronics S-1080) 1 SPST mains rocker switch with Neon indicator (S5) (Jaycar SK-0976, Altronics S-3228) 1 panel-mount 240VAC Neon indicator 1 M205 or 3AG 250VAC 10A panel-mount safety fuseholder (Jaycar SZ-2028 or SZ-2025; Altronics S-5992) 1 M205 or 3AG 10A fast-blow fuse (to suit fuse holder) 1 7.5A mains cord and plug with earth (or 10A cord and plug for controlling appliances rated at up to 2500W) 1 10A mains panel socket with side wire entry (Jaycar PS4094; Altronics P-8241) 2 20°C/W TO-220 mini heatsinks, 19 x 19 x 10mm (Jaycar HH8502) 1 cordgrip grommet for 6.5mm OD mains cable 1 18-pin DIL IC socket 9 100mm cable ties 8 6.4mm insulated spade crimp connectors for 1mm2 wire 2 4.8mm insulated spade crimp connectors for 1mm2 wire 1 chassis-mount 6.4mm spade terminal 2 PC-mount 6.4mm spade terminals 4 M4 x 10mm screws 4 M4 nuts 4 M3 x 6mm screws 2 M3 x 10mm screws 1 M3 x 15mm screw 3 M3 nuts 1 200mm length of 7.5A blue mains wire (or 10A for up to 2500W) 1 200mm length of 7.5A brown mains wire (or 10A for up to 2500W) 1 100mm length of 10mm heatshrink tubing 1 50mm length of 4mm heatshrink tubing 1 170mm length of 1mm enamelled copper wire 1 25mm length of 0.8mm tinned copper wire 6 PC stakes 1 10kW top-adjust multi-turn trimpot (code 103) (VR1) er’s secondary leads (6.3V, 0V, 6.3V), plus another two to terminate switch S4’s leads. Diodes D1-D5 are next on the list. Make sure these are oriented correctly before soldering their leads. That done, install a socket for IC1, making sure its notched end matches the position shown on Fig.2. Do not install IC1 yet – that step comes later, after the power 30  Silicon Chip Semiconductors 1 PIC16F88-I/P microcontroller programmed with 1010208A. hex 1 7805 5V regulator (REG1) 1 7812 12V regulator (REG2) 1 BC337 NPN transistor (Q1) 5 1N4004 1A diodes (D1-D5) Capacitors 1 470mF 25V PC electrolytic 1 100mF 25V PC electrolytic 2 100mF 16V PC electrolytic 3 10mF 16V PC electrolytic 1 100nF MKT polyester (code 104 or 100n) 1 100nF ceramic (code 104 or 100n) Resistors (1/4W, 1%) 1 22kW 1 470W 0.5W 4 10kW 1 330W 3 1kW supply has been checked. Next on the list are the capacitors. Be sure to orient the electrolytics as shown and note that the 100nF ceramic capacitor goes in next to the 433MHz receiver module. The other two 100nF capacitors are MKT polyester types. One is just below one end of IC1, while the other is just above BCD switch S1. Regulators REG1 & REG2 are both mounted horizontally on the PC board. The first step is to bend their leads down through 90° so that they will go through their PC board holes. In each case, the regulator’s two outer leads are bent down 8mm from its body, while its centre lead is bent down 5mm from the body. That done, secure each regulator together with a U-shaped heatsink to the PC board using an M3 x 10mm machine screw and nut. Be careful not to get the regulators mixed up – the 7805 (REG1) mounts on the righthand side. Tighten each assembly down firmly before solder their leads and trimming them to length. Do not solder the regulator leads before tightening the mounting screws, as this could stress the soldered joints and fracture the board tracks. Next, install trimpot VR1, transistor Q1 and the three BCD switches. Be sure to use the correct BCD switch at each location (S1 is the 0-9 switch) and note that they must be oriented exactly as shown. Follow these parts with the 433MHz receiver module, again taking care to ensure it goes in the right way around. The pin designations are all clearly labelled on the back of the module and you can also match the orientation of the module against the photographs. The antenna is made using a 170mm length of 1mm enamelled copper wire. This is formed into a gentle spiral by winding it over a 10mm mandril (eg, a drill). As shown in Fig.2, it extends from the antenna PC stake to a hole in one corner of the PC board, immediately to the right of REG1. Be sure to scrape away the enamel insulation from the wire ends before soldering it in position. Note: for safety reasons, the antenna must be fully enclosed in the plastic case. Under no circumstances should it be mounted externally, nor should any part of the antenna protrude from the enclosure. The reason for this is siliconchip.com.au INSTALL CABLE TIES AT LOCATIONS INDICATED BY RED ARROWS This is the view inside the completed UHF Remote Mains Switch. Be sure to use insulated spade connectors for the connections to the mains switch and the relay and insulate all other connections with heatshrink sleeving to ensure safety. The wiring must be secured using cable ties at the positions indicated by the arrows. siliconchip.com.au February 2008  31 This close-up view shows how the antenna is mounted at one end of the PC board. It’s made by winding a 170mm length of 1mm enamelled copper wire onto a 10mm mandril (eg, a drill). that if a mains wire comes adrift inside the case, it may contact low-voltage circuitry and so the antenna may also become live (ie, at 240V AC) . The next step is to install two PCmount 6.4mm spade terminals immediately to the right of RLY1 (these are used to terminate the leads from the relay’s coil). That done, the relay and transformer can both be secured in position using M4 screws, nuts and star washers. Note the earth lug that’s fitted under one of the transformer mounting screws. Before fitting this, be sure to scrape away the enamel from the transformer mounting foot to ensure good contact. The board assembly can now be completed by mounting the mains terminal block. Secure it using an M3 x 15mm screw, nut and lockwasher. Final assembly The UHF Remote Mains Switch is housed in an ABS enclosure measur- ing 171 x 121 x 55mm. If you buy a kit, then the box will probably be supplied pre-punched and with screened lettering on the front panel (or an adhesive label). If not, then you will have to drill the holes yourself. Basically, you will have to drill and shape holes in one end of the case for the fuseholder, the mains switch and the cordgrip grommet. That done, you will have to drill holes in the lid for the GPO socket, the neon indicator and for pushbutton switch S4. The diagram for the GPO cutout is shown in the bottom righthand corner of Fig.2. The large cutout 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. Once the drilling is completed, install the PC board, safety fuseholder and power switch and check where the 2-way terminal block should be positioned. Mark and drill a mounting hole for this in the PC board, then Install the UHF receiver module with its crystal towards BCD switch S1 as shown here. 32  Silicon Chip secure it in position using an M3 x 15mm screw and nut. The PC board can then be secured inside the case using four M3 x 6mm screws. Note that you must use the correct safety fuseholder, as specified in the parts list. Do not substitute for this part, as other fuseholders may pose a shock hazard. It’s now simply a matter of completing the wiring as shown in Fig.2. All wiring must be run using mainsrated cable. You can use 7.5A cable throughout for powering appliances rated up to 1875W but be sure to use 10A cable where indicated if you want to power appliances that are rated up to 2500W. Note that the brown cable is used for the Active wiring while the blue cable is used for the Neutral leads. The green/yellow-striped wire is used for the earth wiring only and the Earth lead from the mains cord must go straight to the GPO. The connections to the mains switch (S5) and the relay are made via insulated crimp connectors. Be sure to use insulated connectors here as these terminals all operate at 240VAC. By the way, a proper ratchet-driven crimp tool (see panel) is an absolute necessity to attach the connectors to the leads. Low-cost automotive type crimpers are definitely not suitable here, as their use would result in unreliable and unsafe connections. The leads to fuseholder (F1) and the neon lamp are soldered to their respective terminals. Note that the Active lead from the mains cord goes to the terminal on the end of the fuseholder. Note also that all these connections should all be insulated with heatshrink sleeving – see photos. Similarly, use heatshrink sleeving to insulate switch S4’s terminals. The transformer secondary leads and the leads from S4 connect to adjacent PC stakes. Once again, these connections should all be insulated with heatshrink sleeving to ensure reliability. Take great care when making the connections to the mains socket (GPO). In particular, be sure to run the leads to their correct terminals (the GPO is clearly labelled) and do the screws up nice and tight so that the leads are held securely. Similarly, make sure that the leads to the mains terminal block are firmly secured. Once the wiring is complete, it siliconchip.com.au Table 2: Setting The Timeout Period Switch S3 Setting Timeout Period (Minutes) 0 1 2 3 4 5 6 7 8 9 A B C D E F No timeout 1 2.55 4.5 5.5 6.75 10 15.5 30 45 60 90 120 150 180 240 Follow this table to adjust BCD switch S3 to set the required timeout period (if required). A setting of “0” gives no timeout period – ie, the unit will only switch off in response to an “Off” signal from the transmitter or the Water Tank Level Meter Base Station. should be secured using cable ties. This is done so that if a mains wire does come loose, it cannot move and make contact with any low-voltage components on the PC board. One of the photographs clearly shows the locations of the cable ties. Note that the Active and Neutral leads are secured to the GPO using cable ties which pass through the holes in its moulding. Testing Before applying power, check your wiring carefully and make sure that all mains connections are covered in heatshrink tubing. That done, check that there is a 10A fuse inside the fuseholder and note that IC1 should be left out of its socket for the time being. When testing and making adjustments, the UHF Remote Mains Switch will be operated with the lid open. During this procedure, you must not touch any of the 240VAC wiring. This includes the transformer primary leads plus all wiring to the mains socket, neon lamp, switch S5, the fuseholder, the relay and the mains terminal block. Although all connections should be insulated, it’s wise to be careful. In particular, note that the relay’s wiper (COM) contact, the fuseholder’s siliconchip.com.au terminals and the switch wiper will all be at 240VAC if the device is plugged into the mains, even if switch S5 is off. If your house has a safety switch (earth leakage detection) installed then this can provide added protection. If not, then consider using a portable safety switch for this part of the test. Apply power and use your DMM to check that there is 5V (4.9-5.1V is acceptable) between pins 14 & 5 of IC1’s socket. If this is correct, switch off, disconnect the mains plug from the wall socket and install IC1. Take care to ensure that IC1 goes in the right way around – see Fig.2. Next, set the DMM to the 250VAC range, apply power again and carefully check the voltage between the Active and Neutral sides of the mains terminal block (ie, measure the mains voltage). That done, press switch S4 to turn on the relay, set your DMM to read volts DC and adjust multi-turn trimpot VR1 so the DC voltage between TP1 and TP GND is 1% of the mains voltage reading. For example, if the mains voltage is 250V AC then adjust VR1 for a reading at TP1 of 2.50VDC. Similarly, if the mains voltage is 230VAC, VR1 would be set for a reading of 2.30V at TP1. Note that for a European mains voltage of 220VAC, VR1 should be adjusted so that TP1 reads 2.5V when the mains voltage is 220VAC. In other words set VR1 so that the DC voltage at TP1 is 1.14% of the mains voltage. This will set the brownout cut-out to 192VAC. Setting the BCD switches If you intend using this unit with a Water Tank Level Meter Base Station, then you will have to set BCD switches S1 and S2 accordingly. It’s just a matter of setting S1 to the pump number and S2 to the encode value to match both the Water Tank Level Meter and the Base Station. BCD switch S3 sets the timer period – see Table 2. Usually, S3 is set to 0 for controlling pumps that deliver to a household water supply. If pumping between tanks, then the timer can act as a back-up to switch off the pump if the level meter fails. GPO power at power-up Another option is for the UHF Remote Mains Switch to apply power to the GPO at power-up. This feature is handy if you want the unit to automatically supply power to an appliance when power is restored after a blackout; eg, to a pump that supplies water to a house. To enable this option, all you have to do is press and hold down switch S4 when powering up the UHF Remote Mains Switch. Once enabled, exactly the same procedure is used to disable this option. Your UHF Remote Mains Switch is now complete. Be sure to disconnect the mains lead from the wall socket when fitting the lid and be careful not to pinch any of the leads to the mains socket. Provided you’ve dressed the leads correctly and secured them with cable ties, the leads should fold back neatly into the case when the lid is placed in position. Transmitter Now then, what about the optional transmitter unit for those who wish to use the UHF Remote Mains Switch in a stand-alone application? Well, that’s fully described in the followSC ing article. Check These Important Safety Points (1) Use the specified plastic case to house this project and note that the antenna must be fully enclosed inside the case. DO NOT use a metal case. (2) Use mains-rated cable for all wiring connections and insulate all soldered terminals with heatshrink tubing. Use insulated spade crimp connectors for all connections to the mains switch and relay and be sure to use a ratchet-driven crimping tool to properly secure the spade lugs to the leads. (3) Secure the mains wiring and all other wiring connections with cable ties (see photo), so that they cannot move if they come adrift. Make sure that the wiring to the GPO is correct and that it is properly secured. (4) All wiring to the mains switch, mains socket, neon indicator, relay contacts, the 2-way terminal block & the transformer primary operates at 240VAC (ie,mains potential). Do not touch any of this wiring or the connections to any of these these parts while this device is plugged into the mains. DO NOT attempt to build this device unless you know what you are doing and are familiar with high-voltage wiring. February 2008  33