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The 2014 – improved version – of our popular electronic thermostat By JIM ROWE Here’s a new and improved version of our very popular TempMaster electronic thermostat. It’s ideal for converting a chest freezer into an energy-efficient fridge, converting a fridge into a wine cooler or controlling heaters in home-brew setups, hatcheries and fish tanks. It controls the fridge/freezer or heater directly via its own power cable, so there’s no need to modify its internal wiring. It can even be adapted to control 12V or 24V fridges or freezers. tempMASTER Mk3 O ur new TempMaster is smaller, easier to adjust, has a wider temperature range and is now virtually immune to relay chatter problems. The previous version of the TempMaster was described in the February 2009 issue of SILICON CHIP and it has been very popular but as with most products, actual field use demonstrated that improvements can be made. Some common problems involved ‘relay chatter’ and motor switch-on/ switch-off ‘stuttering’ when controlling fridges. Typically, readers also wanted a different temperature 62  Silicon Chip range – either above or below the range of 2-19°C we had given the TempMaster Mk2. We had in mind a number of changes and improvements to the February 2009 design but things were brought to a head by a design recently submitted by reader Alan Wilson. He effectively solved the noise sensitivity and relay chattering problem by providing a fast attack/slow decay filtering function, employing the previously unused second comparator in the IC package. So our new version of the TempMaster includes his modification. siliconchip.com.au We have also expanded the temperature adjustment range, reduced the already low quiescent power consumption and it now fits into a smaller and cheaper case. So here is the list of improvements and changes: • Much greater noise immunity and hence almost complete freedom from annoying relay chatter and motor switching stutter. • A much wider overall temperature adjustment range (from -23°C to +47°C), which can be set by changing ‘max’ and ‘min’ jumper shunts rather than having to change resistor values. • The use of a more efficient low-voltage regulator and CMOS dual op amp, lowering the quiescent power consumption to below 45 milliwatts (0.045 watts) – equating to 1.08Wh/day while running from battery. How it works Fig.1 shows the basic configuration of the TempMaster Mk3 when it’s set up for controlling a fridge or freezer. The heart of the circuit is the remotely-mounted LM335Z temperature sensor, TS1. The LM335Z acts similarly to a special kind of zener diode but its voltage drop varies in direct proportion to absolute temperature, having a value of 0V at 0 Kelvin (-273°C) and rising linearly by 10mV for every Kelvin (or °C) rise in temperature. This is shown in the graph of Fig.2. At a temperature of -10°C (263K), the voltage drop of the LM335Z is very close to 2.63V. Similarly at 40°C (313K), it rises to 3.13V. We use this change in voltage to control the temperature of our fridge/freezer or heater by comparing the sensor’s voltage with a preset reference voltage. The comparison is made by IC1a, one section of an LMC6482AIN dual CMOS op amp which is connected as a comparator. For cooling control, the sensor voltage VSENSOR is fed to the non-inverting input, pin 3, of IC1a via a 1.2kΩ resistor, while the reference voltage VREF is taken from adjustment trimpot VR1 and fed to the inverting input, pin 2. If VSENSOR is lower than VREF (because the temperature of TS1 is lower than that corresponding to VREF), the output of IC1a will be low – close to 0V. But if the temperature being sensed by TS1 should increase to the set threshold, VSENSOR will rise just above VREF and the output of IC1a will switch high – to almost +12V. Heating The reverse sequence of events happens when the circuit is configured for heating control rather than cooling. In this mode, sensor TS1’s voltage VSENSOR is fed to the inverting input of IC1a, while the reference voltage VREF is fed to IC1a’s non-inverting input via the 1.2kΩ resistor. (In other words, the two voltages are swapped around.) As a result the output of IC1a remains low while ever VSENSOR is higher than VREF but switches high as soon as VSENSOR falls below VREF. Hysteresis Returning to the cooling control configuration shown in Fig.1, note the 10MΩ resistor connected between the output of IC1a (pin 1) and its non-inverting input (pin 3). This is to provide a very small amount of positive feedback. We do this so that once pin 1 has switched high, the actual voltage fed to pin 3 will be slightly higher than the sensor voltage VSENSOR (about 1mV higher, in fact). As a result, VSENSOR needs to fall slightly below VREF before the voltage at pin 3 drops to the level matching VREF. But then pin 1 suddenly switches low again, which causes the voltage at pin 3 to drop back to VSENSOR. So the effect of this small amount of positive feedback is to create a small difference between the comparator’s turn-on and turn-off voltage levels (and the corresponding temperatures). This is called “hysteresis” and is designed to minimise any tendency for the comparator to oscillate or ‘stutter’ at the switching thresholds – especially the turn-off threshold. Now we come to the improvement proposed by reader Alan Wilson, involving diodes D3, D4 and IC1b. Together with the 10μF capacitor and the second 10MΩ resistor, D3 & D4 form a fast-attack/slow-decay filter. This works in conjunction with IC1b (connected as a comparator) to ensure that transistor Q1 and the power switching relay are able to turn on quite rapidly as soon as the output of IC1a switches high but cannot switch off again for 30 seconds or so after the output of IC1a has dropped low. This is because the 10μF capacitor can charge up quickly via D3 but can only discharge quite slowly via D4 and the 10MΩ resistor – and only when the output of IC1a has dropped low, in any case. IC1b also has a modest amount of positive feedback ap+12V +5V REG 220k 1.8k 5.6k +3.2V REFERENCE VOLTS RANGE SELECT SET TEMP VR1 2.5k 2 500 3 IC1a 1 K A 1.2k A K TS1 LM335Z + – 220k FAST RISE, SLOW DECAY 6 IC1b 4 10F RELAY OUTPUT SWITCHING 5 (D3) INPUT COMPARATOR Q1 BC327 C 10M 10M E 4.7k 220k (D4) 8 VSENSOR TEMP SENSOR B IC1: LMC6482AIN VREF +2.5V 22k +8V WHEN RELAY OFF, +4V WHEN RELAY ON 7 K D2 DELAY COMPARATOR A TEMPMASTER BASIC CONFIGURATION – COOLING CONTROL Fig.1: this simplified circuit shows the basic operation. The full circuit is shown overleaf in Fig.3. siliconchip.com.au August 2014  63 LM335Z SENSOR VOLTAGE 3.13 3.12 3.11 3.10 3.09 3.08 3.07 3.06 3.05 3.04 3.03 3.02 3.01 3.00 2.99 2.98 2.97 2.96 2.95 2.94 2.93 2.92 2.91 2.90 2.89 2.88 2.87 2.86 2.85 2.84 2.83 2.82 2.81 2.80 2.79 2.78 2.77 2.76 2.75 2.74 2.73 2.72 2.71 2.70 2.69 2.68 2.67 2.66 2.65 2.64 2.63 –10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 263K 270K 273K 280K 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 313K 300K 310K 290K 293K 303K 283K TEMPERATURE – DEGREES CELSIUS (KELVINS IN GREEN) Fig.2: the LM335Z sensor voltage changes with its temperature, and that change is linear from way below zero up to above the boiling point of water. Actual operating range is -40°C to +100°C. plied, via the 220kΩ resistor linking pins 7 and 5. This also helps ensure that there can be no relay stuttering during either turn-off or turn-on. The full circuit Now let’s look at the full circuit of Fig.3 to consider the finer points of operation. Temperature sensor TS1 plugs into socket CON2 which connects to test point TP2 and one end pin of links LK1 and LK2. It also connects to the regulated +5.0V rail via a 5.6kΩ resistor, which feeds the sensor a small bias current. The regulated +5.0V rail is provided by REG1, an LP2950ACZ device. The reference voltage to be compared with the sensor voltage is derived from the same regulated +5.0V supply rail, via a voltage divider formed by the 1.8kΩ resistor (at the top) – plus a string of 200Ω and 100Ω resistors and finally the 2.4kΩ resistor at the bottom. The divider provides a set of five different tapping voltages, with +3.2V available at the top and +2.5V at the bottom. Link set LK3 allows you to select one of three voltage levels as the temperature range maximum, while link set LK4 allows you to select one of another three voltages as the temp range minimum. The temperature setting ‘fine tuning’ is done using VR1, 64  Silicon Chip a 500Ω multi-turn trimpot. Its two ends are connected to LK3 and LK4 respectively, so whichever maximum and minimum temperatures have been selected using these links, VR1 then allows you to select any specific VREF in this range, corresponding to your desired threshold or ‘set point’ temperature. For example, if you have set LK3 to position 3 to give a maximum VREF of 2.7V, and have also set LK4 to position 3 to give a minimum VREF of 2.5V, VR1 will then let you select any voltage between these two limits. This means you’ll be able to select any threshold temperature between about -3°C and -23°C. Get the idea? Note that the selected reference voltage VREF is made available at test point TP1, while the sensor voltage VSENSOR is always available at TP2. These two voltages go to links LK2 and LK1, which are used to select either the heating (H) or cooling (C) mode of operation. As mentioned earlier, this involves simply swapping which of the two voltages, VREF and VSENSOR, is passed to the non-inverting input of IC1a, and which is fed to the inverting input. The rest of the circuit is very similar to the basic outline in Fig.1. The only real differences are the addition of small filter capacitors between both inputs of IC1a and IC1b (to siliconchip.com.au Fig.3: this full circuit of our new TempMaster has many similarities with the simplified version of Fig.1. While the control circuitry operates from low voltage and is isolated, it is switching mains so must be regarded as dangerous. improve noise immunity), and the addition of LED1 with its 6.8kΩ series resistor, across the relay coil. This is to provide an indication of when the relay is energised. All of the circuit operates from 12V DC fed via CON1, polarity protection diode D1 and a 10Ω resistor which limits the current through zener diode ZD1 if the voltage rises above 16V. The supply can come from a 12V plugpack or battery, and since the current drain is only around 100mA when the relay is switched on and less than 4mA when it’s off, only a small battery or plugpack is required. This should make the TempMaster Mk3 very suitable for use with solar power systems. Construction Nearly all of the components used in the TempMaster siliconchip.com.au circuit are mounted on a PCB measuring 104 x 80mm and coded 21108141. The board has rounded cut-outs in each corner so it fits inside a sealed polycarbonate case measuring 115 x 90 x 55mm, sitting on the tapped pillars moulded into the bottom of the case. We have used a rugged 12V relay (RLY1) rated to switch 250VAC at up to 30A so that it can easily handle typical fridge, freezer or heater loads. The connectors for the 12V DC input (CON1) and remote temperature sensor TS1 (CON2) are mounted on the right-hand side of the board, accessed via matching holes on that side of the case. The “set temperature” trimpot VR1 is mounted between these two connectors and is also accessed by a small hole, while the “relay on” indicator LED1 is visible via a similar small hole below CON2. The only components not mounted on the PCB inside the August 2014  65 TempMaster Mk3 itself are the fused IEC mains input connector (CON4) and the switched 3-pin mains outlet or GPO. The latter is mounted on the lid, while the former mounts in the left-hand side of the case (in a matching cut-out). Note that CON4 should be fastened inside the case using two 10mm Nylon screws and Nylon hex nuts. When wiring the board, follow the internal photos and Fig.5 closely. Begin wiring up the board by fitting the three terminal pins (used to provide test points TP1, TP2 and TPG). These go at centre right on the board. Then fit DC input connector CON1, temperature sensor socket CON2 and the two-way terminal block CON3 (used for the relay coil wires). If you want to use a socket for IC1 this can be fitted now as well. You can also mount the two three-way SIL headers for LK1 and LK2, which are located just to the left of TP1. Then fit the two 3x2 DIL headers for LK3 and LK4, which go just above LK2. Next install the various fixed resistors, making sure each one goes in its correct position. Check their values with a DMM just before it’s fitted to the board. Then fit trimpot VR1, between CON1 and CON2. The five non-polarised polyester and MMC capacitors can go in next, followed by the two 10μF tantalums and finally the 470μF electrolytic. Note that the last three are polarised and must go in the correct way around. Then fit diodes D1-D4, zener diode ZD1 and transistor Q1, again paying attention to polarity. LED1 should be mounted vertically and with the bottom of its body about 15mm above the board (the leads will be bent by 90° later). Make sure the LED is orientated so that its ‘flat’ is near the top of the board and its longer anode lead is passing through the lower hole in the board. Then solder REG1, followed by IC1 – soldering it in place if you’re not using an IC socket. Relay RLY1 is attached to the board using two M4 x 10mm machine screws, with flat washers, lockwashers and hex nuts. Before you mount it, you need to cut a small piece from the relay’s mounting flange at the switching contacts end, as shown in Fig.5. (This is to provide clearance for the body of CON4, when it’s fitted later.) The soft plastic can be cut quite easily using a small hacksaw and the cut edges smoothed using a small file. Then mount the relay on the PCB with its coil connection spade terminals at the bottom and its contact connectors at the top, again as shown in Fig.5. Also make sure that you fit the relay mounting screws facing upwards – that is, with their heads under the board and the nuts and washers above the relay mounting flanges. Otherwise the PCB assembly won’t fit properly down inside the case. With the PCB now complete, you drill and cut the various holes needed in the case and its lid. The drilling and cutting details are shown in Fig.7. Note that the cut-out in the rear long side of the case/ box for fused IEC mains inlet CON4 extends almost to the very top – but not quite. Drill and file the cut-out first so Fig.4: the cable connecting the input and output sockets should be cut from a 10A 3-core mains cable offcut. 66  Silicon Chip Full-size photo of the assembled PCB. All components (with the exception of the IEC mains input socket and the GPO) mount on this board. Note the double-insulating layer of heatshrink tubing over the coil wiring between the PCB and the coil spade terminals. that it extends almost to the top of the outer box side and then carefully extend the top using a small file, until CON4 just slips inside. Once the case is prepared, lower the PCB assembly down into the main part of the case until it’s resting on the standoff pillars. Then decide where the leads of LED1 will need to be bent outward by 90°, so it will just protrude from the matching hole in the side of the case. When you have bent the LED leads to achieve this, lower the PCB assembly into the case again and screw it into place using four M3 x 6mm machine screws, which mate with the metal nuts moulded into the standoffs in the bottom of the case. Then fit the IEC mains input connector CON4 into its cut-out and secure it with two M3 x 10mm Nylon screws and nuts. Mount the mains outlet GPO on the case lid, with its ‘backside’ passing through the matching rectangular cutout. This is done by unclipping the outer dress cover plate, to reveal the various recessed mounting holes which are provided. The holes you’ll be using here are those that are spaced 84mm apart, along the ‘east-west’ centreline of the GPO. You need to attach the GPO to the case lid using a pair of 2 x 4.8mm & 1 x 6.8mm CRIMPED FEMALE SPADE CONNECTORS BARE ENDS SECURED IN MAINS GPO A E 4.8mm N 10A FLEXIBLE 250VAC MAINS LEAD – LEAVE OUTER SHEATH ON 4.8mm 6.8mm 10 10 10 20 ~100mm 20 15 20 siliconchip.com.au REG1 10F LP2950-N D1 + CABLE TIE 4004 16V 1.8k 5.6k 14180112 4102 C 3kM RETSAMPMET ZD1 1F + 10 CON4 (MOUNTED ON LH END OF BOX) 470F 12V IN C LMC6482 10M 4148 A SENSOR CON2 LED1 ON 4148 47nF 100nF 4.7k 22k Q1 BC327 D4 H TPG LK2 220k 2.7nF COIL D3 TOP TP2 + E SET TEMP 500 15T 10F 220k 10M HEATSHRINK INSULATION BOT S RLY1 SY-4040 VR1 LK4 H CON1 2.4k 3 R NOTE: ALL WIRING (OFF THE PCB) MUST BE RUN USING 250VAC RATED CABLE. CONNECTIONS TO CON4 AND THE TERMINALS OF RLY1 MUST BE MADE USING FULLY INSULATED FEMALE SPADE. CONNECTORS. THE LOW-VOLTAGE “COIL” CONNECTIONS TO RLY 1 SHOULD ALSO BE COVERED BY HEATSHRINK INSULATION TO DOUBLE-INSULATE THEM AS THEY ARE LOCATED IN THE “MAINS” SECTION OF THE CASE. 220k 2 T ATTACH CON4 TO BOX END USING M3 NYLON SCREWS AND NUTS NOTE: CUT SMALL PIECE OUT OF RELAY MOUNTING FLANGE AS SHOWN, TO CLEAR BODY OF CON4 C 1 TP1 LK3 30A CONTACTS 3 1nF 2 1.2k 1 N IC1 N LK1 A 100 200 200 100 200 E K A 6.8k GPO (MOUNTED ON LID OF BOX) D2 4004 TO RELAY COIL CABLE TIE CON3 INVERTED L-SHAPED INSULATION BARRIER Fig.5: follow this component overlay and wiring diagram exactly to ensure your TempMaster is completely safe. Note particularly the use of cable ties to ensure all connecting wires are securely held – that’s also the reason we use a piece of flexible 10A mains cable with its outer sheath left in place as much as possible. M4 x 15mm pan-head screws passing down through these holes and fitted with star lockwashers and M4 nuts inside. Tighten these up firmly to make sure that the GPO can’t work loose. Don’t fit the GPO’s dress cover plate at this stage. It’s clipped on later - after the lid is finally screwed onto the case, because the cover plate just interferes with the lidto-case assembly screw heads. Next you need to prepare the mains connection cables which link the GPO to the IEC mains connector and the contacts of RLY1. Fig.4 shows a same-size diagram of the mains connecting cable. It makes sense to use a length of thin mains-rated LM335Z (FLAT SIDE DOWN) BROWN WIRE TO THIS LEAD M3 x 9mm COUNTERSINK HEAD SCREWS WITH STAR LOCKWASHERS AND M3 NUTS CUT ADJ LEAD SHORT RED WIRE TO CENTRE LEAD 2 x 25mm LENGTHS OF 2.5mm HEATSHRINK 3-METRE LENGTH OF 2-CORE RIBBON CABLE 10A flex for this as you will not only obtain the insulation level required but leaving the outer sheath on the cable also keeps the conductors together. Note that the blue (Neutral) and green/yellow (Earth) wires from the GPO have 4.8mm fully insulated female spade connectors crimped firmly to their ‘far ends’ while the brown (Active) wire has a 6.8mm spade connector attached. The shorter brown (Active) wire connecting from the IEC connector active to the relay switch contact also has insulated spade connectors at both ends, one 4.8mm and one 6.8mm wide. Make sure you attach all of these spade connectors very firmly using a rachet-type crimp connector, so they will 30mm LENGTH OF 5mm DIA HEATSHRINK 1 2 3 25 x 50mm ALUMINIUM HEATSINK PLATE 4 3.5mm JACK PLUG (RED WIRE TO TIP) 5 Fig.6: steps in wiring the LM335Z temperature sensor. In step 1, the unwanted “ADJ” lead is cut off, two wires are soldered to the other pins and then covered with heatshrink. In step 2, the heatshrink is slid up and over the soldered leads and shrunk, followed by a larger length of heatshrink over the whole assembly. In step 4, you secure the sensor to a heatsink, then finally in step 5 connect the two wires to a 3.5mm jack plug. siliconchip.com.au August 2014  67 way that it can swing around and make contact with any of the low voltage wiring. You can also fit another cable tie around the wires from the relay coil to CON3, to make sure these will also hold each other in place. Now you can fit jumper shunts to the two 3-way SIL header strips LK1 and LK2, in the centre of the PCB, depending on whether you’re going to be using the TempMaster to control cooling or heating. You should also fit jumper shunts to one of the three positions on both DIL header strips LK3 and LK4, to set the maximum and minimum of the temperature adjustment range you wish to use. 5 19 4 4 A A CUTOUT FOR FUSED IEC MAINS INLET 25 24 24 4.5 4.5 27 9 3 36 (REAR LONG SIDE OF BOX) CL A 7.5 7.5 15 B 15.5 15 C Safety insulation A 15.5 14 12 (FRONT LONG SIDE OF BOX) CL (ALL DIMENSIONS IN MILLIMETRES) 27 27 54 x 34.5 CUTOUT FOR REAR OF GPO 16 D D CL 18.5 42 42 (LID OF BOX) HOLE SIZES: HOLES A: 3.0mm DIAM. HOLE B: 10.0mm DIAM. HOLE C: 8.0mm DIAM. HOLES D: 4.0mm DIAM. CL give reliable long-term connections. Lastly you can make up the two short wires which are used to connect the coil of RLY1 to terminal block CON3. These can be made up from medium-duty insulated hookup wire, with each one having a 4.8mm insulated female spade connector crimped to one end. Once all of these wires have been 68  Silicon Chip Fig.7: cutouts and holes required in the polycarbonate case. prepared, you can use them all to connect everything up as shown in Fig.5. This will complete the wiring of the TempMaster Mk3, but before you screw on the lid of the case to finish assembly, fit a Nylon cable tie to the mains wiring as shown in Fig.5 and the internal photo. This is to ensure that should any of the spade connectors somehow work loose, there is no Because there are low voltage components in close proximity to the mains outlet when the case is closed, it is essential to make sure they can never come in contact with each other. We do this with an insulating barrier, cut from a piece of Presspahn, Elephantide or similar insulation and bent it into an “L”-shape (as shown in Fig.8). This slides down the edge of the relay, keeping the mains and low voltage sides separate. A dollop of glue on the edge of the relay and the surface of the PCB alongside will hold the barrier in place when the top goes on. Fit the rubber sealing strip around the groove in the underside of the case lid and then screw the lid to the case using the four screws provided. Then you’ll be able to clip the cover plate back on the GPO, to complete the assembly of the TempMaster Mk3 itself. Making the remote sensor The details for the temperature sensor are shown Fig.6. The first step is to clip short the unwanted third lead of the LM335Z sensor and then solder the ends of a 2-core ribbon cable to the other two leads after slipping 25mm lengths of 2.5mm diameter heatshrink sleeving over each one. After the solder cools, the sleeves are then moved up until they butt hard against the body of the LM335Z. Then they are heated to shrink them in place (step 2). Then a 30mm length of 5mm diameter heatshrink sleeving is slipped along the cable and over the other sleeves, and heated in turn to shrink it in place as well (step 3). Prepare the sensor’s heatsink assemsiliconchip.com.au A close-up of the heatsink and clamp assembly for the LM335Z temperature sensor. Parts List – TempMaster Mk3 bly by drilling two 3.5mm diameter holes on the centre line of the 50 x 25mm aluminium plate, 18mm apart. The bottom of both holes should be countersunk to accept countersink-head screws passed up from underneath. Next make the 30 x 10mm piece of 1mm aluminium into a clamp piece, by bending its central 8mm section into a half-round shape to fit snugly over the LM335Z body. After this drill 3.5mm holes in the flat ends of this clamp piece, 18mm apart again to match the holes in the larger plate. You should then be able to assemble the probe with the LM335Z clamped to the top of the plate ‘flat side down’, and the screws tightened down using M3 nuts and star lockwashers (step 4). Complete the sensor assembly by fitting the 3.5mm mono jack plug to the other end of the two-core ribbon cable, connecting the red wire to the ‘tip’ lug and the brown wire to the ‘sleeve’ lug (step 5). Initial checks Before doing anything else, use your multimeter or DMM (set to a low ohms range) to check between the Earth pin of the IEC connector (CON4) and the Earth outlet of the GPO. You should get a reading of zero ohms here (this checks the integrity of the Earth connection). Then fit a 10A slow-blow M205 fuse into the fuseholder in the IEC connector. Do not connect 230VAC power to the unit until you have done the set-up adjustments. All setup is done using the low-voltage supply only. DO NOT CONNECT 230VAC power without the lid in 89 x 75mm PIECE OF INSULATION MATERIAL (eg PRESSPAHN, ELEPHANTIDE, ETC) 45mm (score and bend down 90°) 30mm Fig.8: L-shaped insulation barrier inserted between the low voltage components and the mains wiring. siliconchip.com.au 1 Polycarbonate case, light grey, 115 x 90 x 55mm (Jaycar HB-6216 or similar) 1 PCB, code 21108141, 80 x 104mm 1 SPST relay, 30A contacts with 12V/100mA coil (Jaycar SY-4040 or similar) 1 2.1mm or 2.5mm concentric DC connector, PC-mounting, to suit plugpack (CON1) 1 3.5mm switched stereo socket, PC-mounting (CON2) 1 2-way terminal block, PC-mounting (CON3) 2 3-pin SIL header strip, PC-mounting (LK1, LK2) 2 3x2-pin DIL header strip, PC-mounting (LK3, LK4) 4 Jumper shunts 3 1mm diameter PCB terminal pins 1 IEC panel-mount mains socket with fuse (CON4) 1 Single 250VAC switched General Purpose Outlet (GPO) 1 10A M205 fuse cartridge, slow blow 1 105 x 75mm piece Presspahn insulation (Jaycar HG-9985) 4 M3 6mm machine screws, pan head 2 M4 10mm machine screws, pan head 2 M4 15mm machine screws, pan head 4 M4 hex nuts with flat & lockwashers 2 M3 10mm Nylon screws, pan head, with Nylon hex nuts 1 205mm length of 10A 3-core mains flex 1 60mm length of 10A brown mains wire 2 70mm lengths of medium duty insulated hookup wire 6 Nylon cable ties 2 6.8mm insulated female spade connectors for 1.2mm wire 5 4.8mm insulated female spade connectors for 1mm wire 1 3m length of 2-conductor ribbon cable 1 25 x 50 x 3mm aluminium sheet 1 30 x 10 x 1mm aluminium sheet 2 25mm lengths of 2.5mm heatshrink sleeving 1 30mm length of 5.0mm heatshrink sleeving 2 M3 9mm machine screws, countersink head 2 M3 hex nuts & star lockwashers 1 3.5mm mono jack plug Semiconductors 1 LMC6482AIN dual CMOS op amp (IC1) 1 LP2950ACZ-5 micropower LDO regulator (REG1) 1 LM335Z temperature sensor (TS1) 1 BC327 PNP transistor (Q1) JAYCAR 1 16V 1W zener diode (ZD1) ELECTRONICS will 1 3mm red LED (LED1) release a ‘short 2 1N4004 1A diodes (D1,D2) form’ kit for the 2 1N4148 signal diodes (D3,D4) TempMaster Mk3 Capacitors 1 470µF 25V RB electrolytic 2 10µF 16V tag tantalum 1 1µF monolithic multilayer ceramic 1 100nF monolithic multilayer ceramic 1 47nF MKT or ceramic/MMC 1 2.7nF MKT or ceramic/MMC 1 1nF MKT or ceramic/MMC shortly – includes PCB with relay and onboard components plus temperature sensor and mounting plate. Cat KC-5529, $39.95 Resistors (0.25W 1% unless specified) 2 10MΩ 3 220kΩ 1 22kΩ 1 6.8kΩ 1 5.6kΩ 1 2.4kΩ 1 1.8kΩ 1 1.2kΩ 3 200Ω 2 100Ω 1 10Ω 0.5W 5% 1 500Ω horizontal 10-turn cermet trimpot (VR1) 1 4.7kΩ August 2014  69 Insulated terminals with extra heatshrink Internal views of the TempMaster Mk3 – above, with the PCB in place and at right, fully assembled with shield. place, to eliminate the risk of electric shock. Mainsrated wires Setting it up This is done by adjusting trimpot VR1 (using a small screwdriver through the access hole in the front panel) to produce the reference voltage level at test point TP1 corresponding to the average temperature you want the TempMaster to maintain. First plug the 12V DC cable from your plug pack or battery supply into CON1 at the right-hand end of the box – do not plug the mains supply in yet. Then use your DMM to measure the DC voltage between TP1 and TPG. The voltage should be somewhere between the maximum and minimum levels you have set using the links of LK3 and LK4. Select the temperature you want from the horizontal axis of the graph in Fig.2, and adjust VR1 to obtain the corresponding DC value on the vertical axis. All that remains now is to mount the remote sensor inside the fridge or freezer cabinet, or inside the hothouse or seed germinating cabinet, attaching the sensor’s heatsink plate to the side of the cabinet using two short lengths of ‘gaffer’ tape. Then you can run its ribbon cable outside, holding it Resistor Colour Codes             No. 2 3 1 1 1 1 1 1 1 3 2 1 70  Silicon Chip Value 10MΩ 220kΩ 22kΩ 6.8kΩ 5.6kΩ 4.7kΩ 2.4kΩ 1.8kΩ 1.2kΩ 200Ω 100Ω 10Ω Pressboard shield      4-Band Code (1%) brown black blue brown red red yellow brown red red orange brown blue grey red brown green blue red brown yellow violet red brown red yellow red brown brown grey red brown brown red red brown red black brown brown brown black brown brown brown black black brown No 1 1 1 1 1 Capacitor Codes Value 1µF 100nF 47nF 2.7nF 1nF µF Value IEC Code EIA Code 1µF 1000n 105 0.1µF 100n 104 0.047µF 47n 473 0.0027µF 2n7 272 0.001µF 1n 102 5-Band Code (1%) brown black black green brown red red black orange brown red red black red brown blue grey black brown brown green blue black brown brown yellow violet black brown brown red yellow black brown brown brown grey black brown brown brown red black brown brown red black black black brown brown black black black brown brown black black gold brown siliconchip.com.au TempMaster Connection Options These diagrams show three different ways that the TempMaster Mk3 can be connected up to control the temperature of a fridge, freezer or heater set-up. Which one you use will depend on whether your fridge/freezer/heater operates from 230VAC or 12V DC, and also whether you will be running it from the AC mains or from a battery supply. Option A shows the simplest arrangement, where a 230VAC fridge/freezer or heater is to be operated directly from the mains supply. The 12V DC needed by the TempMaster itself can be supplied either by a small ‘plug pack’ DC supply or from a 12V SLA battery which is kept ‘topped up’ by a suitable charger. Option B shows how a 230VAC fridge/ freezer or heater can be connected to a 12V/230VAC power inverter, in a home or building which relies on solar or wind generated power. The TempMaster itself can be powered from the main battery, along with the power inverter used to operate the fridge/ freezer/heater. Because there is no current whatever drawn from the TempMaster’s IEC mains input socket when the TempMaster has switched off the power to the fridge/freezer/ heater, the inverter should be able to drop back to ‘sleep’ mode at these times. Option C shows how to connect things up when the TempMaster is to be used with a 12V fridge/freezer and a solar power system. In this case, you MUST replace both of the TempMaster’s ‘mains’ connectors with suitable low voltage plugs and sockets, to make sure that they can’t be accidentally connected to 230VAC. 23 0V AC WALL OUTLETS (GPOs) 230VAC FRIDGE/FREEZER (OR HEATER) IEC MAINS CORD TEMPERATURE SENSOR TEMPMASTER Mk3 (12V DC LEAD) A 12V DC PLUG PACK (OR CHARGER + 12V SLA BATTERY) 12V–230VAC INVERTER IEC MAINS CORD USE WITH 230V FRIDGE/FREEZER/ HEATER, MAINS POWER 230VAC FRIDGE/FREEZER (OR HEATER) TEMPMASTER Mk3 (12V DC LEAD) TEMPERATURE SENSOR WIND GENERATOR + – CHARGING CONTROLLER B BATTERY USE WITH SOLAR/WIND POWER, 230V FRIDGE/ FREEZER/HEATER SOLAR PANEL LOW VOLTAGE PLUGS & SOCKETS 12V FRIDGE/FREEZER (12V DC LEAD) TEMPERATURE SENSOR TEMPMASTER Mk3 WIND GENERATOR + – CHARGING CONTROLLER BATTERY C USE WITH SOLAR/WIND POWER & 12V FRIDGE/FREEZER SOLAR PANEL down with further strips of gaffer tape so it will pass neatly mometer placed inside the cabinet for a while. You can see when the TempMaster is switching power under the rubber door seal when the door is closed. If you mount the thermostat case on the wall just behind to the compressor or heater simply by watching LED1. If you need to adjust the average temperature up or down, the fridge/freezer or heater, the plug on the end of the ribthis is done quite easily by adjusting trimpot VR1 using a bon cable can be plugged into CON2 on the lower front of small screwdriver, through the small hole in the front of the case to complete the job. the case (between the holes for CON1 and CON2). SC Now you can unplug the power cord of the fridge/ freezer/heating cabinet from its original GPO socket SILICON and plug it instead into the GPO on the top of the Mk3 CHIP TempMaster. Then when you connect the TempMaster’s own IEC mains connector to the original OUTPUT 12V DC IN TEMP ADJUST GPO via a suitable IEC mains cable, the complete ON SENSOR SET POINT system will begin working. (You do have to flick the switch on the TempMaster’s GPO to the ‘on’ + – position, of course!) If you want to make sure that the thermostat is holding the fridge/freezer/heater to the temperature Full-size artwork for the TempMaster Mk3 front panel, which you want, this can be done quite easily using a ther- mounts on the box side. The GPO fastens through the top of the box. TEMPMASTER THERMOSTAT siliconchip.com.au August 2014  71