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A precision Temperature Logger and Controller Part 2 – by Leonid Lerner Last month we introduced this temperature logger and controller, based on the $99 Dick Smith Q1437 Digital Thermometer. Here are the construction, testing and setup details – along with a couple of pertinent warnings! T in soldering to this component. In he first step in construction is the third lead soldered to the earth practice, one wire is soldered to pin 11 to make and solder in the interas shown in the photograph and diaof the HT1621 while the connection to face to the Dick Smith Q1437 gram. While the prototype used white, pin 12 is made at the respective pin of Digital Thermometer. This is achieved there’s a lot less chance of error if the MF430F quad flat package. by opening the case and wiring in a “rainbow” ribbon cable is used for this. Using a magnifying glass as an aid, 2.5mm stereo jack socket, which in The HT1621 comes in a dual-in-line the well-tinned end of a 1mm soldering turn connects (externally) to the PC via surface-mount package with pins only iron tip is touched against the outer a 2.5mm jack plug, a suitable length 0.5mm wide, so great care is required extreme of each pin to be soldered, of shielded stereo cable and a DB25 depositing a very small bump of solder. (parallel printer port) plug. Now the tinned end of the ribbon Remove the protective rubber sleeve cable is placed on top of the pin and of the Digital Thermometer and then compressed against it by pressure unscrew four screws, including from the soldering iron tip for the two for the battery comparta few seconds so the solder ment. Then gently prise the top flows and a connection is made. and bottom covers apart. They Inspect the joints carefully to will remain loosely connected ensure no shorting has occurred by the two leads to the piezo – use the very minimum amount sounder which is glued to the of solder consistent with making bottom cover. a good connection. Next, a short (~100mm) An 8mm hole is then drilled length of ribbon cable is End-on view of the DSE Q-1437 Digital Thermometer. in the top end of the case to alstripped and soldered to the The two sets of thermocouple sockets are original; low fitting of the 2.5mm stereo WR (pin 12) and data (pin the 2.5mm stereo socket is an addition to interface socket, as shown below left. The 11) lines of the HT1621, with with this project, as described above. 86  Silicon Chip siliconchip.com.au A close-up view inside the DSE Digital Thermometer with a magnified view above, showing the three connection points required, along with the new 2.5mm socket in the top of the case. Soldering to these fine IC pins is NOT easy to do – be extremely careful – a hot iron with a fine tip plus a steady hand are de rigeur! Inspect carefully for any solder bridges. thermocouple connectors will have to be temporarily unscrewed from the panel to allow the new socket to be inserted. The ribbon cable wires are then soldered to the socket while ensuring the earth lead is soldered to the correct terminal. The signal leads should be soldered to the signal pins on the socket so that the body, tip and ring (BTR) connect with the same pins on the 2.5mm plug. In other words, pin 11 of the HT1621 goes to pin 12 of the DB25M connector to the PC while pin 12 of the HT1621 goes to pin 13 of the PC connector. As mentioned last month, connection to the PC printer port is made by means of a 2-core shielded cable to which a 2.5mm stereo plug is connected at the Q1437 end, while a DB25 connector is soldered at the PC end. The two 680pF capacitors are soldered directly at the DB25 connector from pins 12 and 13 to the earth at pin 25. You will also need to make the cable connection to the Triac load controller box, which we will look at shortly. First, carefully re-assemble the Q1437 Thermometer in the reverse order to disassembly, ensuring that the added ribbon cable does not foul anywhere. Load controller PC board This uses a single sided PC board measuring 87 x 54mm and coded 10101101. The complete component siliconchip.com.au overlay and wiring diagram (combined) is shown in Fig.3. Assemble the PC board as shown in this diagram – there are only seven components and only the semiconductors (Triac and Triac trigger) are polarised. Do not substitute the specified insulated tab Triac for another – your safety depends on it. Note that the legs of the Triac are “cranked” to allow them to fit into the PC board. It is a good idea to leave the Triac until last to ensure that its mounting hole lines up with the hole drilled for it in the box side. Also ensure that the 10nF capacitor is an “X2” class for mains rating and safety. Do not substitute another type, even if it has a higher voltage rating. Mounting the PC board The PC board is mounted in a suitable diecast aluminium box. This will need holes cut out to accept IEC male and female chassis mount sockets, a mains safety fuse and a DB9 socket. You will also need to drill holes for the mounting for the IEC socket mounting screws, a separate earth and the single screw for the insulated tab Triac. Ch eck The se Imp ort ant Saf ety Po int s (1) Use mains-rated hookup wire for the connections between the PC boar d and the DB9 connector. These leads must be kept as short as possible and secured at both ends using Nylon cable ties. That way, if a lead comes adrift, it cannot move and mains-operated components on the PC contact any board or the terminals of the IEC sock ets. It’s also a good idea to further secure the lead s at both ends using clea sure to use a type that’s acetic acid free) r silicone sealant (be . (2) Use mains-rated cable for all conn ections to the IEC sockets and complete the terminals using heatshrink tubing. ly insulate Alternatively, use insulated spade lugs (you must use a ratchet-driven crimping tool to properly secure the spade lugs to the leads). (3) Secure the high-voltage wiring betw een the PC board and the IEC sockets with ties. Again, the idea is to make it impo cable ssible for any leads to move and cont act other parts of the circuit if they come adrift. (4) Fit an extra locking nut to secure the earth solder lug nut into position, so that it cannot poss in place. This nut locks the first ibly come undone. (5) Do not substitute another Triac for the specified BTA10-600B. This parti cular an insulated tab which means it can be fastened to the metal case with completeTriac has safety. (6) Part of the circuitry on the PC boar d operates at mains potential (as do the terminals of the IEC sockets). Do not touch or work on plugged into the mains. DO NOT attem any part of this circuitry while this device is pt to build this device unless you know what you are doing and are familiar with mains voltage wiring techniques. February 2010  87 230V AC MALE INLET SOLDER TAG & STAR LOCK WASHER FOR BOX EARTH (SECURE WITH EXTRA LOCK NUT) SAFETY FUSE HOLDER (REAR) N A E 10mm LONG M3 SCREW TRIAC1 BTA10-600B SIDE OF BOX M3 FLAT WASHER, STAR LOCKWASHER AND NUT INSULATED TAB TRIAC CRANKED LEADS PC BOARD 1k 10nF X2 39  1W HEATSHRINK SLEEVES OVER JOINTS AND TAGS 390 POWER CONTROL PC BOARD 130 0102 © 10110101 MOC 3041 OPTO1 HEATSHRINK SLEEVES OVER JOINTS AND TAGS CAUTION! COMPONENTS AND TRACKS INSIDE DOTTED LINE ALSO OPERATE AT 230V MAINS POTENTIAL. MAINS RATED WIRES E A N 230V AC FEMALE OUTLET NOTE: ALL LEADS MUST BE MAINS RATED Make sure that you follow explicitly the wiring details above. All wiring must be done with 250VAC-rated cable. Note that the earth wiring is soldered to the earth pins of the two IEC sockets and to a separate solder lug which connects to the diecast metal case via a screw. Not immediately obvious in the diagram is a locknut on the earth screw – a good idea to ensure that nothing can ever vibrate its way loose. The earth plane of the PC board is not connected to the mains earth of the case. It connects to the earth of the PC via the 9-pin DB9 socket, 2-way ribbon or shielded cable and DB25 plug (the same plug which connects back to the Q1437 Digital Thermometer) Finally two short lengths of mains-rated wire are used to make a connection between the input to the MOC3041 and PCB earth and the DB9 socket. This pin is connected externally to pin 2 of the parallel port. 3 5 (DB9 FEMALE) Fig.3: follow these diagrams explicitly to ensure mains wiring safety standards are followed – remember, there is a direct (wired) connection between this and your PC. The purpose of locknuts, lockwashers, cable ties and the like is to ensure that if the worst happens and a wire dislodges after time, it cannot contact any mains voltages. The PC board is designed to keep the mains voltage and low-voltage sections as separated as possible. Note the “crank” in the Triac leads (shown above) – again, this gives extra separation to keep mains voltages away from the metal case. Incidentally, if you don’t need mains control or are not confident with mains projects, the modified thermometer and logging software works fine on its own! down for longer than three seconds. This ensures that the AUTO-OFF function, which turns the thermometer off after 30 minutes, is disabled. At this stage click the Run PC Mode button at the top right of the GUI and a display indicating the time, the two temperatures, the current duty cycle of the Triac control signal and the message ‘Running” should appear at the bottom of the GUI. In addition, provided the thermocouples are plugged in to the thermometer, two curves, blue and black, should commence to be drawn out on the screen. The temperature limits corresponding to the top and bottom of the graph, are designated in the appropriate boxes next to the vertical axis at the top and bottom of the screen, while the times are indicated in the corresponding boxes next to the horizontal axis. Checkout time First, we will check operation of the thermometer interface. The project software consists of two files. T_Controller.exe is the main file containing the GUI (graphical user interface), while Porttalk.sys is the system device driver carrying out the low-level port communication. The latter file needs to be copied to the /Windows/system32/drivers directory on your computer while the former can be located in any convenient folder. Next T_controller.exe is run and the GUI screen (as shown below) should appear. Connect the PC to the Q1437 digital thermometer and turn the thermometer on by holding the green ON button 88  Silicon Chip Fig.4: here’s the GUI screen which you should see after running the T_controller.exe software. siliconchip.com.au If it is desired to rescale or reposition the graph, these values can be changed during the acquisition while the curves are being drawn and the ‘Redraw’ button pressed. Once sufficient data has been gathered the ‘Abort’ button can be pressed. Acquisition then ceases and the temperature data gathered so far is saved in a text file labelled Tdata#. txt, with # being the number label entered in the edit box next to the ‘Abort’ button. A new acquisition can be started afresh at any stage now by pressing the ‘Run PC Mode’ button, however if the file label has not been changed when ‘Abort’ is next pressed, the data from the previous run will be overwritten. The data in the text file is presented in the form of two vertical columns corresponding to the two temperature channels at one-second intervals. The temperatures are presented as the actual temperature in degrees times 10 to allow representation of the decimal component of the measurement using whole numbers. Should the Q1437 be turned off or the interface disconnected at any stage, the PC will reach a point where it tries to read the Q1437 and ‘hang’ due to lack of data on the line. It will commence functioning properly again once the connection with the Q1437 has been re-established. To switch the logger off, either the ‘Abort’ or ‘Exit’ buttons should be pressed before turning off the Q1437. Starting the Triac load controller A mains load can now be connected to the Triac load controller. Use a load which will give a direct indication of duty cycle, such as a heat gun (which you will hear changing as the duty cycle changes) or a large incandescent lamp. The mains plug is now attached to the controller and with the cable to the PC disconnected, no power should flow to the load. The control cable from the PC parallel port is now attached and a representative duty figure, such as 50%, entered into the GUI. A temperature higher than ambient with a duration greater than zero is entered into the respective GUI boxes. Upon pressing the ‘Run PC Mode’ button the load should start to be pulse at about a 1:1 mark to space ratio, ie, half second on, half second off. If the unit passed all the above tests it is ready to be used as a temperature logger and controller. Just enter the time (in seconds) and temperature (in degrees) with the requisite number of set points (up to four) in the temperature program box, and press ‘Run PC mode’. If during the course of data logging it is desired to investigate the graph being produced over a different range of time and/or temperature values than initially chosen, new values are entered into the corresponding boxes, and the ‘Redraw’ button pressed to replot the graph. In the same fashion the temperature program can be altered ‘on the run’, with new set points reflected by changing locations of the horizontal set temperature lines on the graph. When the ‘Abort’ button is pressed all data logged so far will be recorded and can be inspected with Wordpad, imported into a spreadsheet, etc. Finally, if you are not confident of constructing mains projects, or even if you just want a temperature logger, you can simply do the mods to the thermometer and it will function perfectly as a stand-alone device (ie, without the Triac load controller attached). SC siliconchip.com.au Australia’s Best Value Scopes? You decide! Colour display. USB host for USB memory stick FFT and Math functions Up to 1000 Waveforms record and playback USB device - PC software and cable included Models from 25 MHz to 100 MHz *** 5 year warranty *** Starting Prices 25MHz colour UQ2025C just $579 inc. GST INTRODUCTORY SPECIAL: * 60MHz Colour UQ2062C only $695 including GST NZ orders welcome. Postage at cost. * Offer expires 31/3/2010 Contact TRIO Smartcal now! 1300-853-407 or visit www.triosmartcal.com.au to learn more. 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