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Easy-to-build de s i g n h a s t w o i n dep en den t l y programmable relay outputs By GREG RADION Low-Cost Analog On-Off Controller Have you ever wanted to control a device based on an analog signal level? Perhaps you want to fill a water tank automatically or control exhaust fans based on humidity or temperature. Well now, you can – provided you have a sensor that gives an analog voltage or current output. T his Analog On-Off Controller unit switch­ es two independent relays based on the signal level at its input. The “on” and “off” levels for each relay are easily set using only a screwdriver and you can monitor the level of the signal on an LCD panel meter if desired. With its fully adjustable design, the controller accepts inputs in the range of 0-10V or 0-20mA. Its current input capability also means that it can be used with industrial sensors 40  Silicon Chip that provide a 4-20mA current loop interface. Best of all, this unit can be put together for about $65.00 and is very easy to build. All the parts are mounted on two PC boards which are stacked together and connected using rainbow cable. How it works The Analog On-Off Controller is essentially a group of voltage comparators with additional circuitry to translate input signals to a usable voltage range, as well as flipflops to hold the two outputs in their last “on” or “off” state. The complete circuit for the controller appears in Fig.1. Apart from op amp IC1 and relays REL & REL2, the circuit is powered via a 7805 +5V regulator (VREG1). Diode D1 is included in series with the 12V input to protect against supply polarity reversal. An LT1014 precision op amp (IC1c) buffers the input signal. This op amp siliconchip.com.au siliconchip.com.au July 2006  41 Fig.1: the input signal is buffered and normalised to a 0-1V level by an LT1014 quad precision op amp (IC1). The signal is then split into two channels, each consisting of two LM339 voltage comparators with independently programmable rising and falling threshold levels. A pair of D type flipflops provides a setreset function to hold the last event and drive the business end – two high-current relays. is connected as a differential amplifier with unity gain, as determined by the four 200kW resistors used in its input and feedback networks. Jumper JP6 is installed when the controller is used with a current loop type sensor, thus allowing current to flow through the 62W resistor and generate a voltage between the differential inputs. The output from IC1c is fed into a second op amp (IC1d), also configured as a differential amplifier. In this case, a 50kW trimpot (VR1) takes the place of two resistors in the amplifier’s input network, allowing it to be trimmed for a gain of 0-2. This is used to scale the input signal to 1V full-scale ahead of the comparator network. For example, when operating with a 0-20mA input range, the gain would be adjusted to produce 1V at the op amp’s output with 20mA of loop current. For a 0-5V input range, the gain would be adjusted to produce 1V out with 5V in. For a 4-20mA input range, the gain would be adjusted to produce 1.25V with 20mA in. An offset of 0.25V (adjustable with VR2) can be applied to the inverting input via JP2 to subtract from the signal on the non-inverting input, thus producing 0-1V (representing 0-100% of scale) at the output. A simple shunt regulator comprised of a 3.3V zener diode (D2) and 5.6kW resistor forms a stable reference for the circuit. The regulator’s output feeds two 20kW trimpots (VR2 & VR3), with their wiper voltages buffered by two unity-gain op amps (IC1a & IC1b). VR3 is trimmed for 1V at the output of IC1b (pin 7). Further, the reference voltage for each comparator can be adjusted within the 0-1V range using trimpots VLO1, VHI1, VLO2 & VHI2. The outputs of comparators IC2b and IC2c will go high (near +5V) when the voltage at their non-inverting in- Fig.2: follow this parts layout diagram and the screened printing on the PC board during assembly. Leave out the two LEDs (L1 & L2) and links JP4 & JP5 if you’ve purchased the optional display panel! Table 1: Resistor Colour Codes o o o o o o o o   No. 6 4 2 10 5 2 1 42  Silicon Chip Value 10MW 200kW 100kW 10kW 5.6kW 2.2kW 62W 4-Band Code (1%) brown black blue brown red black yellow brown brown black yellow brown brown black orange brown green blue red brown red red red brown blue red black brown 5-Band Code (1%) brown black black green brown red black black orange brown brown black black orange brown brown black black red brown green blue black brown brown red red black brown brown blue red black gold brown siliconchip.com.au Par t s Lis t 1 double-sided PC board, 87 x 107mm 2 3-way 5.08mm 10A terminal blocks 3 2-way 5.08mm 10A terminal blocks 2 7A/240VAC relays with 12V DC coils 1 12-way 2.54mm DIL header strip (break in half for 2 x 6-way strips) 1 3-way 2.54mm SIL header strip (JP1/JP2) 5 jumper shunts 3 14-pin IC sockets 1 50kW 10-turn trimpot (VR1) 2 20kW 10-turn trimpots (VR2, VR3) 4 2kW trimpots (VHI1, VLO1, VHI2, VLO2) This is the fully assembled controller board. Check the text for the various linking options. puts is greater than that of the reference level on their inverting inputs. Conversely, the outputs of IC2a and IC2d will go high when the voltage at their inverting inputs is less than that of the reference level on their non-inverting inputs. A high value (10MW) resistor is used to feed a small amount of each comparator’s output signal back to its input, eliminating oscillations near the switching point. Each comparator pair drives the “set” and “reset” inputs of a D type flipflop (IC3a & IC3b). A high from the comparator connected to the set input will cause the Q output to latch high, biasing its associated transistor into conduction and energising the relay. Conversely, a high on the reset input causes the Q output to go low, switching off the relay. As shown, the outputs of each comparator pair can be steered to either flipflop input, depending on the position of the A and B jumpers. This allows each output to be switched on or off on a rising or falling input signal level. Finally, the flipflops’ clock inputs are connected to simple RC networks so that a short positive-going pulse is applied at power up. As the D inputs are grounded, this ensures that the Q outputs are reset (low) at startup and that both relays are initially off. calibrated to suit the intended application. All you need is a digital multimeter and a voltage (or current) source set to the maximum input signal level. To begin, connect a 12V DC power supply to the Vs and COM inputs. Remember to disconnect power when making jumper or link changes. Calibration and setup • • Before use, the controller must be siliconchip.com.au For 4-20mA operation: • • • • • • • Install a link at JP6. Install a jumper in the JP1 position. Supply 20mA to the inputs (IN+ & IN-). Adjust VR1 to give 1.25V at TP1. Move the jumper at JP1 to position JP2. Adjust VR2 to give 1.00V at TP1. Adjust VR3 to give 1.00V at TP6. For 0-20mA operation: • • • • • Install a link at JP6. Install a jumper in the JP1 position. Supply 20mA to the inputs (IN+ & IN-). Adjust VR1 to give 1.00V at TP1. Adjust VR3 to give 1.00V at TP6. For 0-5V (or 0-10V) operation: • • • Remove link at JP6. Install a jumper in the JP1 position. Supply 5.00V (or 10.00V for 0-10V operation) to the inputs (IN+ & IN-). Adjust VR1 to give 1.00V at TP1. Adjust VR3 to give 1.00V at TP6. Semiconductors 1 7805 +5V regulator (VREG1) 1 LT1014 quad precision op amp (IC1) 1 LM339 quad comparator (IC2) 1 4013 dual flipflop (IC3) 3 1N4004 silicon diodes (D1,D3, D4) 1 1N4728 3.3V zener diode (D2) 2 BC548 transistors (Q1, Q2) 2 3mm red LEDs (L1, L2) Capacitors 1 100mF 35V electrolytic 10 100nF 50V monolithic ceramic Resistors (0.25W, 1%) 6 10MW 5 5.6kW 4 200kW 2 2.2kW 2 100kW 1 62W 10 10kW Parts For Optional Display Panel 1 PC board, 57 x 107mm 1 PM128E LCD panel meter 1 DPDT mini toggle switch 1 single pole 12-way rotary switch 1 knob to suit above 4 6mm M3 screws 4 20mm M3 screws 4 10mm M3 tapped spacers 4 25mm M3 tapped spacers 150mm length of 16-way ribbon cable Once calibration is complete, each relay can be set to operate on either a rising (jumper in position in “A”) July 2006  43 actly the same manner using test pads HI2 and LO2 and trimpots VHI2 and VLO2, respectively. Front panel add-on This view shows the controller board wired to the optional front-panel display board. The display board carries an LCD panel meter which makes it easy to adjust the on/off trip levels without using a multimeter (see Fig.3 for the wiring details). or falling (jumper in position “B”) input signal. The rising and falling trigger levels can then be set for both outputs. To set the rising (high) level for the first relay output, measure the voltage at the test pad labelled “HI1” and adjust it using trimpot VHI1. A reading of 0.8V will mean that the relay switches on at 80% of the maximum input signal, while 0.6V equates to 60%, etc. To set the falling (low) level for the first relay output, measure the voltage at the test pad labelled “LO1” and adjust it using trimpot VLO1. A reading of 0.2V will mean that the relay switches off at 20%, while 0.3V equates to 30%, etc. The other output is adjusted in ex- The Analog On-Off Con­troll­er can be ordered with an optional LCD front panel, allowing convenient adjustment and monitoring of the unit without the use of a multimeter. The front panel consists of an LCD panel meter mounted on a small section of PC board alongside a 5-position rotary switch and a toggle switch. Two LEDs are also provided to indicate relay activation. The panel mounts above the main board on four 35mm spacers. Rotating the switch through its five available positions shows the input current/voltage level as a percentage of the maximum, as well as the programmed on and off points of each of the relays. Setting of the four switching levels is easily performed with the front panel meter. Simply rotate the switch through positions Hi1, Lo1, Hi2 and Lo2 and adjust trimpots VHI1, VLO1, VHI2 and VLO2 as described earlier. Note that VR1, VR2 and VR3 are set during initial calibration and must not be altered here. The “duty” switch on the front panel swaps the on and off levels of Relay 1 with those of Relay 2. This is useful when a “duty” and “standby” setup is required, allowing the operation of two devices to be periodically swapped to ensure even wear. Example application The Analog On-Off Controller has a large range of potential applications. Let’s look at a couple that involve water pumping. For example, suppose two pumps are to be used to fill a water tank. The “duty” pump (connected to relay 1) could be set to start when the level drops below 40% and stop when it rises above 65%, whereas the “standby” pump (connected to relay 2) could start at 35% and stop at 70%. Table 1: Application Examples Operation Relay 1 Relay 2 Two pumps filling a tank Duty pump Standby pump A (falling) Two pumps emptying a tank Duty pump Standby pump B (rising) 44  Silicon Chip Jumper Block 1 Jumper Block 2 Hi1 Lo1 Hi2 Lo2 B (falling) 65.0 40.0 70.0 35.0 A (rising) 60.0 50.0 70.0 55.0 siliconchip.com.au Fig.3: here’s how to wire the display board to the controller. Leave enough wire length to allow the two boards to be stacked together later. Note that several links (circled in red) must be placed on the LCD panel meter before use. In four places, the pads can simply be shorted with blobs of solder. For the “P1” position, a short length of wire will be required instead. A similar example can be given for emptying a tank. Suppose that the “duty” pump starts at a level of 60% and stops when the level falls below 50%, whereas the “standby” pump starts when the level reaches 70% and stops when it falls below 55%. Table 1 shows the settings required for these two examples. Extended operation In some applications, more than two devices must be controlled from a single input signal. For example, you may have a duty pump switching on at 80% and two standby pumps switching on at 85% and 90%. This is easily accommodated by installing a second controller and making a few minor changes. First, connect the “VOUT” terminals of the two controllers together. The input signal is then connected to the first controller only, while link JP3 is removed from the second controller. Assembly Before starting construction, note that the two LEDs and links JP4 & JP5 siliconchip.com.au must not be installed if you will be fitting the optional display panel. Using the overlay diagram in Fig.2 as your guide, begin by installing wire links in place of jumpers JP3-JP6, noting that JP3 is only fitted when using a current loop input. Next, install 3-way header pins for jumpers JP1 & JP2 and 6-way headers for jumper blocks “1” and “2”. The resistors, capacitors, diodes (D1-D4) and transistors (Q1 & Q2) can all go in next. Note that resistor R6 (shown in red in Fig.2) is not required – just leave this location empty. Take care with the orientation of the 100mF electrolytic capacitor – be sure to align its positive lead with the “+” marking on the overlay. In addition, the banded (cathode) ends of the diodes and the flat sides of the transistors must be oriented as shown. After this, solder in the trimpots (VR1-VR3, VLO1, VHI1, VLO2 & VHI2), LEDs (L1 & L2), voltage regulator (VREG1) and IC sockets. Again, take care to ensure that all these parts are correctly orientated. Don’t plug in Suggested Uses For The Controller The Analog On-Off Controller could be used to: • Operate one or two pumps based on the level in a tank or well. • Operate pumps in a duty-standby arrangement. • Regulate pressure using a compressor and a pressure sensor. • Control a heating or cooling appliance using a temperature sensor. • Regulate humidity using exhaust fans and a humidity sensor. • Control chemical dosing, given an appropriate sensor. • Almost anywhere that an analog signal level can be used to turn a device on and off. July 2006  45 The display board is wired to the main controller board using short lengths of rainbow cable. The two boards are then stacked together using spacers – see Fig.4. Fig.4: the display panel board is mounted above the main board on four 35mm tapped spacers, in turn assembled from shorter 25mm and 10mm items. Here’s how it goes together. the ICs until after you’ve checked the power supply. All that remains now are the terminal blocks and relays; install these now and perform a final check of your board before applying power. Now connect a 12 DC source to the Vs and COM terminals and measure the voltage at the output of the regulator, accessible at pins 7 & 14 of IC3’s socket. Obviously, the supply rail should measure 5V (±5%). If all is well, power off and insert the IC’s in their sockets, noting that the notched (pin 1) ends must be oriented as shown. Display panel The optional display panel is as- Where To Buy A Kit Of Parts The Analog On Off Controller was developed by Ocean Controls, who retain the design copyright. The controller is available as a kit of parts or preassembled and tested. Prices at time of publication were: Analog On-Off Controller kit: $59 +GST ($70 +GST assembled). Analog On-Off Controller kit and Display Panel kit: $84 +GST ($99 assembled, $119 with IP65 box). PM-128E Panel Meter (included with the Display Panel option): $20 + GST. Note that these prices do not include postage charges. Check out the Ocean Controls website at www.oceancontrols.com.au for more information or phone (03) 5983 1163 to order. 46  Silicon Chip sembled next. The PC board provides pads for just two 3mm red LEDs – so install these first. The anode side of the LEDs (indicated by the longer lead) goes into the holes marked with a “+” on the silkscreen. Leave about 5-10mm of length when trimming the leads, so that wires can be attached later. Once the LEDs are in place, mount the LCD panel meter, rotary switch and toggle switch. Note that the rotary switch must be programmed for 5-position operation before mounting. This is easily achieved by inserting the tab of the ring in hole “5”, so that the switch can only be rotated through the first five positions. Before use, five links must be installed on the LCD panel’s PC board, as shown in Fig.3. Short links J1, J2, DC and 2V with blobs of solder. A wire link will be required to connect “P1” to the “ON” side. Short lengths of ribbon cable can now be used to connect the two boards together, as depicted in Fig.3. That done, mount the display assembly above the main board using tapped spacers and screws as shown in Fig.4. Your Analog On-Off Controller is now ready for use. Remember, if you are going to use it to switch 240VAC mains voltages, the wiring must be installed by a licensed electrician. SC siliconchip.com.au