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Easy-to-solder components; no surface mount devices! By JOHN CLARKE Universal Temperature Alarm This compact alarm can be used to monitor the operating temperature of a whole range of devices. You could use it to monitor your tropical fish tank, your home brew, freezer, fridge, your hot water system or whatever. It can monitor temperatures in the range of -33° to 125° Celsius and provide an alarm when the temperature is above, below or not within a specified temperature range. T his project was originally developed with the specific intention of monitoring a tropical fish tank and to replace our Aquarium Temperature Alarm from the September 2006 issue of SILICON CHIP. Hence the “fishy” front panel in the photo above. The PCB for that project is no longer available and so we decided to revise it and also provide an on-board piezo transducer as the audible alarm. 26  Silicon Chip Having done that, it was quite obvious that the project has much wider applications and so we are presenting it as a Universal Temperature Alarm. Harking back to the original application, if you’re using it to monitor a tropical fish tank, you would normally set the upper temperature limit at 26°C and the lower limit at 24°C – quite a narrow band of temps to keep your fish happy and well. If the temperature drifts outside this range, the piezo transducer will sound and one of the warning LEDs will light – red for hot, blue for cool. On the other hand, for universal monitoring applications, you can set the upper temperature limit as high as 125°C or as low as -33°C; boiling or deep frozen; probably not all that good for fish (unless they’re scaled, cleaned and waiting in the deep freezer. . . and the Universal Temperature Alarm can be used to monitor that as well!). siliconchip.com.au siliconchip.com.au OUT 78L05 10nF E IN GND B C Q1: BC547 PIEZO SOUNDER 150 18k 14 13 Q1 4.7k A D5 K K A B +5V GND OUT 100F K A TP2 UNIVERSAL TEMPERATURE ALARM SLEEVE – + TIP LM335Z SC – + LM335Z 3.5mm JACK PLUG SENSOR1 2016 11 CON1 7 100nF 2 3 IC1a 1 16k HIGH 6 5 TPS IC1b VR2 10k TP1 LOW 1.6k D5 1N4004 TPG 4 6 5 IN 7 IC2b D2 K A REG1 78L05 IC1: LMC6484AIN IC2: LMC6482AIN 100F JP2 LED2 2 1M IC2a 1.6k 8 IC1c 9 4 10 D1–D4: 1N4148 E C 10k A K D4 LOW SELECT 1k K  JP1 LOW A 1k K 1 D1 8 3 100nF 6.8k K A 220k LEDS 12 A D3 K HIGH SELECT K  LED1 A 1M HIGH 100nF VR1 10k CON2 Fig.1: the circuit is based on a window comparator comprising op amps IC2a & IC2b with upper and lower thresholds set by trimpots VR1 & VR2. If the temperature sensor voltage is above or below the limits set by VR1 & VR2, the outputs of IC2a or IC2b will forward bias diodes D3 or D4 respectively and Q1 will be turned off, to allow the oscillator based on IC1d to drive the piezo transducer. A Circuit description The circuit of Fig.1 employs six op amps and an LM335Z temperature sensor. While it may look complicated, only two op amp IC packages are involved and you can put it together easily in an hour or so. Best of all, for those readers who find soldering small components a challenge, no surface mount components are used. (Do we hear a loud cheer?) The six op amps are contained with an LMC6484AIN quad op amp package and an LMC6482AIN dual op amp. Both devices are rail-to-rail which means than their inputs and outputs can swing over the full supply voltage range, which in this case is 5V. Three of the op amps (IC1a, IC1b and IC1c) are used as unity gain buffers and another (IC1d) as an oscillator for the alarm. And two op amps (IC2a and IC2b) make up a window comparator that is the heart of the circuit. Temperature sensing is performed by an LM335Z, fed with current via a 2kΩ resistor from the 5V supply. It produces an output voltage that is directly proportional to temperature in Kelvin. IC1d 220k 220k 10k The unit is housed in a small plastic case and is powered using a 9V to 12V DC plugpack or a 12V battery. A handmade temperature probe connects to the alarm using a 3.5mm jack plug. 2.0k • Small size • Over temperature indicatio n • Under temperature indica tion • Over and under temperatur e alarm • Adjustable upper and low er temperature thresholds • Easy calibration • Selectable over and unde r temperature alarm options +5V Features July 2016  27 VR1,VR2:10k 03105161 Rev.C 1k JP2 C 2016 LED2 LOW D4 4148 D2 100nF 4148 A 1M IC2 16k TP2 LMC6482 PIEZO 1k HIGH JP1 1.6k TP 10nF GND TP1 A LED1 D3 BC547 10k 18k 220k 1.6k IC1 LMC6484AIN 100nF VR1 VR2 CON2 6.8k T S R 2.0k Q1 4.7k 4148 220k 220k TPS 10k 100nF PIEZO 150 1M 4148 4004 D5 CON1 + D1 + 100F REG1 78L05 100F 16150130 Fig.2: assemble all the small components onto the PCB before you mount the piezo transducer. All components are through-hole; no surface mount components have been used, for easy assembly. Kelvin is the temperature scale that begins at absolute zero (the coldest temperature possible), equal to -273.15°C. Also note that it is never expressed as degrees Kelvin, or °K – it is simply K. The sensor output is typically 10mV/K with the output at 0V at 0K. At 0°C (273K) output voltage is typically about 2.73V. The sensor’s output is filtered with a 100nF capacitor to remove any noise that could be picked up in the sensor leads. IC1a then buffers the sensor voltage so it provides a low impedance feed to the window comparator inputs of IC2a and IC2b. Window comparator What is a “window” comparator? Answer: it is pair of comparators which work together to sense whether a voltage is above a set limit (the upper comparator) or below the set limit (the lower comparator). In our circuit, IC2a is the upper comparator and IC2b is the lower comparator. The buffered sensor voltage is applied to inverting input pin 2 of IC2a and non-inverting input pin 5 of IC2b. Each of these op amps needs a reference voltage which is then compared with the buffered sensor voltage. So we need two reference voltages, one for each comparator. IC1c buffers the voltage from the upper threshold trimpot VR1 which is connected between a 6.8kΩ resistor from the 5V supply and a 16kΩ resistor to the 0V supply. The resistors restrict VR1’s wiper range to between about 2.4V and 3.96V. The maximum voltage corresponds to 123°C, while the lower voltage corresponds to -33°C. Note that the LM335Z we used is only suitable for use up to 100°C. However, this wider range is included 28  Silicon Chip so that the alternative LM235Z, rated for up to 125°C, could be used if you wanted to. The connection for the lower threshold trimpot VR2 is a little more complex. Op amp IC1b buffers the voltage from the low side of VR1 and its output connects to the lower side of VR2 while its upper side connects to the output of IC1c (ie, the buffered VR1 output). So VR2 provides the lower threshold adjustment which will always be below (or equal to) the upper threshold voltage. We have set up the circuit so that the lower threshold voltage can never be above the upper threshold voltage, because otherwise the window comparator would not operate correctly. Both the window comparator outputs are high (ie, +5V) when the sensor voltage is between the upper and lower threshold voltage. This is the normal condition for which the alarm does not sound. In this condition, diodes D3 and D4 are reversed biased when the op amp outputs are high (ie, when links JP1 and JP2 are connected). So consider what happens when the monitored temperature goes above or below the specified range. IC2a’s output will go low (0V) when the sensor voltage goes above the threshold voltage set by VR1. Similarly, IC2b’s output will go low Scope1: this is the oscillator waveform produced at the output of IC1d. Despite the supply voltage from REG1 being very close to 5V (actually, 5.0372V) the square wave output has some ringing which increases the measured output swing to 5.5V peak-to-peak. siliconchip.com.au when the sensor voltage goes below the threshold voltage set by VR2. In the former case, D3 is forward biased and in the latter case, D4 is forward biased. In each case, transistor Q1’s base voltage will be pulled down and it will switch off, enabling the alarm signal provided by op amp IC1d to drive the piezo transducer. IC1d is connected as a Schmitt trigger oscillator, with its non-inverting input, pin 12, connected to three 220kΩ resistors. One resistor connects to the +5V supply, the second to 0V and the third to the op amp output. The inverting input is connected to a 10nF capacitor that goes to 0V and to an 18kΩ resistor that connects to the op amp output. The 220kΩ resistors set the input bias and the hysteresis for the Schmitt trigger oscillator. We’ll come back to that point in a moment. When power is applied, the 10nF capacitor at the inverting input, pin 13, is discharged, and therefore the inverting input is low and the output at pin 14 will be high. The 10nF capacitor then commences to charge via the 18kΩ resistor to just over 3.33V, which is the lower threshold set by the 220kΩ resistors. At that point the circuit toggles so that the output at pin 14 goes low and 10nF capacitor discharges towards the lower threshold of 1.66V. This cycle repeats while ever Q1 is off and the result is a square wave of approximately 3.5kHz at the output of IC1d, pin 14. This drives the piezo transducer. Window comparator hysteresis Both the comparators based on IC2a and IC2b incorporate a small amount of hysteresis, as mentioned above. This prevents the op amps from oscillating SECURE WITH AQUARIUM RATED SILICONE SINGLE CORE SHIELDED CABLE Parts list – Universal Temperature Alarm 1 PCB coded 03105161, 78 x 47.6mm 1 UB5 translucent clear or blue case, 83 x 54 x 31mm 1 panel label, 76 x 48mm 1 30mm diameter piezo transducer (Jaycar AB-3440, Altronics S 6140) 1 2.1 or 2.5mm DC socket, PCB moutning (CON1) 1 3.5mm switched stereo jack socket (CON2) 1 3.5mm mono or stereo jack plug 2 M3 tapped 6mm spacers 2 M3 x 5mm machine screws 2 M3 x 5mm Nylon or Polycarbonate screws (or cut down longer threaded screws) 2 2-way pin headers (2.54mm pin spacing) (JP1,JP2) 2 jumper shunts 6 PC stakes 1 1m length single core shielded cable 1 35mm length of 2mm diameter heatshrink tubing 1 ball point pen casing for temperature probe Aquarium rated silicone sealant (Selleys Glass Silicone or equivalent) Semiconductors 1 LMC6484AIN quad CMOS op amp (IC1) 1 LMC6482AIN dual CMOS op amp (IC2) 1 78L05 5V regulator (REG1)* 1 BC547 NPN transistor (Q1) 1 LM335Z or LM235Z temperature sensor (SENSOR1) 4 1N4148 switching diodes (D1-D4) 1 1N4004 diode (D5) 1 3mm red high brightness LED (LED1) 1 3mm blue high brightness LED (LED2) Capacitors 2 100µF 16V PC electrolytic 3 100nF 63V or 100V MKT polyester (code 104 or 0.1) 1 10nF 63V or 100V MKT polyester (code 103 or 0.01) Resistors (0.25W, 1%) 2 1MΩ 3 220kΩ 1 18kΩ 1 16kΩ 1 4.7kΩ 1 2.0kΩ 2 1.6kΩ 2 1kΩ 2 10kΩ multiturn top adjust trimpots (VR1,VR2) on and off at their respective threshold voltages. For IC2a, the 1MΩ resistor and diode D1 pull the non-inverting input slightly lower when IC2a’s output goes low, by about 4mV. The 1.6kΩ resistor to IC1c’s output sets this voltage change. 2 10kΩ 1 150Ω 1 6.8kΩ This effectively shifts the upper threshold voltage detected by IC2a lower by 4mV. So the sensor voltage needs to drop by a further 4mV before the IC2a output will go high again. For IC2b, the 1MΩ resistor and diode D2 pull the non-inverting input BALLPOINT PEN CASING (OR OTHER SUITABLE TUBE) SENSOR 1 INNER CORE FILL BREATHER HOLE WITH AQUARIUM RATED SILICONE Fig.3: here’s how to assemble JACK PLUG COVER a temperature “probe” using the LM335Z precision temperature sensor. siliconchip.com.au * Variation in the 5V output of REG1 can cause an error of ±0.5°C over the typical range of indoor ambient temperatures. If better stability is required, you can substitute an LP2950.5 regulator, which has the same pinout. SHIELD WIRES INNER CORE CONNECTS TO PLUG TIP LUG FILL WITH AQUARIUM RATED SILICONE (BUT AVOID GETTING IT ON WIRING) 3.5mm JACK PLUG SHIELD WIRES CONNECT TO PLUG SLEEVE LUG July 2016  29 The completed Universal Temperature Alarm, shown here in its “aquarium” livery, along with the plug-in temperature probe made from the LM335Z temperature sensor, an old ballpoint pen case and some Aquarium-grade silicone sealant. The lead can be made significantly longer if your application calls for it. Inset bottom right is the business end of the probe, housed in sealant – just make sure you don’t get any sealant on the sensor leads or wires. lower when IC2b’s output goes low by about 4mV. This shifts the sensor voltage lower by 4mV and the actual sensor voltage needs to increase by 4mV before the IC2a output can switch high again. When the sensor voltage goes above the high threshold, this is indicated with LED1. For the sensor voltage below the low threshold, LED2 will light instead. Power for the circuit can come from a 9V or 12V DC plugpack supply or 12V battery. A 5V regulator (REG1) regulates the supply to provide a fixed voltage for the upper and lower threshold settings. The regulator includes 100µF bypass capacitors at its input and output for stability. Construction The Universal Temperature Alarm is entirely constructed on a double-sided PCB coded 03105161 and measuring 78 x 47.6mm. The completed PCB is housed in a UB5 (83 x 54 x 31mm) plastic case. For effect, we used the semi-transparent blue case. Fig.2 shows the PCB overlay. Begin construction by installing the resistors, using a DMM to check the value of each before inserting into the PCB. The resistor colour code table also shows the colour codes for each resistor value. Diodes D1 to D5 can now be installed, taking care to orient correctly and note that D5 is a 1N4004 while the remaining diodes are 1N4148s. IC1 and IC2 can be directly soldered in or IC sockets used. Take care to orient these with the correct polarity. REG1 and Q1 are soldered in now. Don’t get them mixed up as these and the temperature sensor look similar, apart from their type markings PC stakes can be used for the test points and for the piezo connection points. The two 100µF electrolytic capacitors need to be installed with the polarity shown and with the top of these no more than 13mm above the top edge of the PCB. Install the 100nF and 10nF capacitors next. These can be positioned either way round. Then solder in the 2-way pin headers for JP1 and JP2 along with the cell holder. Trimpots VR1 and VR2 can now be installed. These are oriented with their screw adjusters toward CON2 as shown. LED1 and LED2 are mounted so the top of the LED lens is 16mm above the top surface of the PCB. Make sure the longer lead of each LED (the anode) is inserted in the ‘A’ position on the PCB. The red LED is for LED1, the high The PCB is designed to snap into the guides moulded into the sides of the jiffy box. Holes are required to be drilled in one end and the lid, as seen above. 30  Silicon Chip siliconchip.com.au Design, Develop, Manufacture with the latest Solutions! Showcasing new innovations and technology in electronics In the fast paced world of electronics you need to see, test and compare the latest equipment, products and solutions in manufacture and systems development. Make New Connections • Over 90 companies with the latest ideas and innovations • New product, system & component technology releases at the show • Australia’s largest dedicated electronics industry event • New technologies to improve design and manufacturing performance • Meet all the experts with local supply solutions • Attend FREE Seminars Knowledge is Power SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Local and International presenters will present the latest innovations and solutions at this year’s conference. Details at www.smcba.com.au In Association with Supporting Publication Organised by Free Registration online! www.electronex.com.au Technology Park Sydney 14 -15 September J2016 uly 2016  31 siliconchip.com.au Resistor Colour Codes Table 2: SENSOR OUTPUT with respect to Kelvin and °C °C 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Kelvin (K) LM335 output (Add 273.15 assuming to °C) 10mV/K 373.15 368.15 363.15 358.15 353.15 348.15 343.15 338.15 333.15 328.15 323.15 318.15 313.15 308.15 303.15 302.15 301.15 300.15 299.15 298.15 297.15 296.15 295.15 294.15 293.15 292.15 291.15 290.15 289.15 288.15 287.15 286.15 285.15 284.15 283.15 282.15 281.15 280.15 279.15 278.15 277.15 276.15 275.15 274.15 273.15 3.7315V 3.6815V 3.6315V 3.5815V 3.5315V 3.4815V 3.4315V 3.3815V 3.3315V 3.2815V 3.2315V 3.1815V 3.1315V 3.0815V 3.0315V 3.0215V 3.0115V 3.0015V 2.9915V 2.9815V 2.9715V 2.9615V 2.9515V 2.9415V 2.9315V 2.9215V 2.9115V 2.9015V 2.8915V 2.8815V 2.8715V 2.8615V 2.8515V 2.8415V 2.8315V 2.8215V 2.8115V 2.8015V 2.7915V 2.7815V 2.7715V 2.7615V 2.7515V 2.7415V 2.7315V Use this table to set up your Universal Temperature Alarm. The areas highlighted are that of most interest to tropical af-fish-ionados; if you need temperatures not an even 5 or 10° above 30°, extrapolate. 32  Silicon Chip            No. 2 3 1 1 2 1 1 1 1 1 1 Value 1MΩ 220kΩ 18kΩ 16kΩ 10kΩ 6.8kΩ 4.7kΩ 2.0kΩ 1.6kΩ 1kΩ 150Ω 4-Band Code (1%) brown black green brown red red yellow brown brown grey orange brown brown blue orange brown brown black orange brown blue grey red brown red violet red brown red black red brown brown blue red brown brown black red brown brown green brown brown LED (marked on the PCB); similarly the blue LED (LED2) is for low. If the LEDs you have are clear, it’s easy to check if the LED is red or blue using the diode test on a multimeter. The LED should faintly glow to see the colour under test. The piezo transducer is mounted off the PCB, supported on 6mm spacers and secured with M3 screws. Use the two Nylon or polycarbonate screws on the underside of the PCB so that there will be no possibility of shorting between tracks and pads. If necessary, enlarge the mounting holes for the piezo transducer to 3mm to suit the screws. Wires can be soldered to the PC stakes marked ‘piezo’ on the PCB. Using PC stakes allows for short lengths of heatshrink tubing to be placed over the wires and PC stakes to help prevent the wires from breaking off. While the piezo transducer will probably come with red and black wires, the connections required are not polarised and it doesn’t matter which wire is used for each ‘piezo’ position. Temperature sensor Depending on the application, the temperature sensor may need to be made into a probe – eg, suitable for immersion into aquarium water or another solution. We used a ballpoint pen casing such as a BIC for this and removed the ballpoint pen and ink refill and the end cap. Wire up the sensor to single cored shielded cable with the centre conductor going to the + terminal of the LM335Z (the centre pin) and the shield to the – side (See Figs. 1 & 3). Make sure that the shield and centre conductor cannot short together or to the other pin (use short lengths of 5-Band Code (1%) brown black black yellow brown red red black orange brown brown grey black red brown brown blue black red brown brown black black red brown blue grey black brown brown red violet black brown brown red black black brown brown brown blue black brown brown brown black black brown brown brown green black black brown heatshrink if necessary). Pass the shielded cable through the narrow end of the tube and position the sensor at the wider end. Use aquariumrated silicone sealant to make physical contact between the sensor and the inside of the casing and to seal off the end. Make sure the sealant does not make contact with the bare leads on the sensor or the wiring as it may corrode them, due to its acid cure properties. The wire exit is also sealed, again using the aquarium-rated sealant, along with the small air hole in the pen tube if there is one. The opposite end of the cable is soldered to a 3.5mm mono jack plug, which mates with the 3.5mm socket on the temperature alarm. The centre conductor connects to the tip of the plug. Testing and setting up Apply power and plug in the sensor. Measure the voltage between TP GND and TPS. Write down the reading and read the air temperature with as accurate a thermometer as you can lay your hands on. Assuming an ambient temperature of 25°C, the voltage should be somewhere around 2.98V. Typical sensors will be 10mV/K but some may vary from this. From the temperature reading and voltage, you can work out the voltage per Kelvin from your particular sensor. So if you have a reading of 2.95V and the temperature reading on a thermometer is 22°C, this is 295K (you add 273). So 2.95V/295K gives 10mV/K. A different sensor may provide a 3.0V reading for a thermometer reading of 24°C – (297K) gives 3.0V/297K or 10.1mV/K. To set the upper and lower thresholds for the Temperature Alarm, just calculate the voltage for the temperasiliconchip.com.au Same-size drilling template for the lid of a UB5 Jiffy Box. The “fishy” version, with holes marked, can be downloaded from siliconchip.com.au Full kits will be available shortly from all Jaycar Electronics stores – Cat KC5533 <at> $39.95 + . + Over + 9V 50mA + 6.5mm + Sensor input Temperature Under + INTO MODEL RAILWAYS Universal Temperature Alarm IN A BIG WAY? + 3mm + With lots2 ofshows points, multiple ture required. Table how ittracks, reversing JP1 and JP2 are included so you can loops, multiple locos/trains, –you might be is done, assuming a 10mV/K sensor. select whether you want the upper, interested in these from the March 2013 issue The calculation is done by converting lower or both thresholds to sound the Automatic Points Controller the required °C (Supplied temperature to infrared Kelvinsensor alarm. JP1 is inserted for the upper with two boards) by adding 273 (PCB and 09103131/2)........................$13.50 then multiplying threshold alarm and JP2 for the lower Frogby Relay (09103133)............$4.50 this Kelvin value theBoard mV/K value threshold alarm. of your sensor. Capacitor Discharge for Twin-Coil Points Both jumpers inserted will trigger an Motors (PCB 09203131)..................$9.00 So for example if you want an upper alarm when either the upper or lower See and articleapreviews at www.siliconchip.com.au threshold of 26°C lower threshthresholds is exceeded. old of 24°C (typical forORDER aquariumNOW use, AT www.siliconchip.com.au/shop for example), the voltage from the Boxing it sensor for these two temperatures is The Alarm is installed inside a UB5 calculated: the two temperatures are case. Holes are required to be drilled converted to K; 26 + 273 and 24 + in the side for the power input (CON1) 273. These become 299K and 297K. and the sensor connector (CON2). A So for a 10.1mV/K sensor the upper template is available that’s included threshold is 10.1mV x 299 = 3.019V with the front panel artwork. This can and the lower threshold is 10.1mV x be downloaded from the SILICON CHIP 297 = 2.99V. website (www.siliconchip.com.au). Setting up the Universal TemperaTwo versions are available: a simple ture Alarm is done by firstly setting version suitable for general purpose the upper threshold by adjusting VR1 use, or the “fishy” version shown on and monitoring the voltage at TP1 to our prototype. get the reading required for the upper The method of producing and attachthreshold. ing your label are left up to you but we Then the lower threshold is adjusted suggest paper printed labels should be by adjusting VR2 and monitoring TP2 laminated or otherwise enclosed for for the lower threshold voltage. protection and longevity. Finally, fit the lid to the case using the four screws SC supplied with the case. INTO MODEL RAILWAYS IN A BIG WAY? No, not just a single loop – but really into model railways, with lots of points, multiple tracks, reversing loops, multiple locos/trains, DCC controllers – in other words, a passion more than a hobby? SILICON CHIP has published a number of model railway projects over the years – you might be interested in these from the March 2013 issue. If you don’t have that issue, view the preview at www.siliconchip.com.au Automatic Points Controller for Model Railways (Supplied with two infrared sensor boards) (PCB 09103131/2).....................$13.50 Frog Relay Board (09103133)....$4.50 Capacitor Discharge for Twin-Coil Points Motors (PCB 09203131) ........................ $9.00 ORDER NOW AT www.siliconchip.com.au/shop Projects with SIZZLE! Two high-voltage projects which use the same PCB: High Energy Electronic Ignition for Cars Use to replace failed ignition module or to upgrade a mechanical ignition system Published in Nov/Dec 2012 (siliconchip.com.au/project/ignition) Jacob's Ladder A spectacular (and noisy! ) display of crackling, menacing sparks as they mysteriously climb the “ladder” Published in Nov/Dec 2013 (siliconchip.com.au/ project/jacobs) Parts available from programmed PIC SILICON CHIP On-Line Shop: PCB, IGBT (siliconchip.com.au/shop) YouLook can for see a preview of these details of all projects at and all projects at siliconchip.com.au siliconchip.com.au/articles/contentssearch siliconchip.com.au July 2016  33