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Aquarium Temperature Alarm By PETER SMITH Protect your tropical fish with this low-cost water temperature alarm! You can build it to monitor any temperature range you wish, just by changing a couple of lines of software code. I T’S COMMON KNOWLEDGE that the water in a tropical fish tank must be maintained within a relatively narrow temperature band – typically around 24°C. In most small home aquariums, this is achieved using a thermostatic heater. When the temperature drops below a preset level, the heater switches on and when it rises above a higher preset, it switches off. Most aquariums are also equipped with a permanently installed thermometer, allowing the operation of the heating system to be checked at a glance. And that’s basically it – nothing more elaborate than this is required while everything is working normally. But consider the outcome if the 74  Silicon Chip heater were to fail due to an opencircuit element, stuck thermostat or extended mains power failure. If a problem like this occurred at an inopportune time such as when you are away on holidays, would the failure go unnoticed by others in the household? And even if you were there, would you detect the problem soon enough to take remedial action? This is where the Aquarium Temperature Alarm comes in. When the water temperature falls outside a predetermined range, a raucous two-tone alarm sounds to alert anyone in the vicinity of the problem. Need more noise? That’s not a problem either, as we’ve made provision for triggering an external alarm system via an optional open-collector output. This could be wired to one sector of a house alarm, which could also power the Aquarium Temperature Alarm for continued monitoring during a mains power failure. Alternatively, the output could be wired to our SMS Controller project (see the October & November 2004 issues) and/or the PICAXE NetServer (described in this issue) for alerting and monitoring worldwide! How it works The Aquarium Temperature Alarm is based around the popular PICAXE-08M microcontroller from Revolution Education (see Fig.1). Although initially developed for the education market, these versatile little devices are cheap (less than $6) and readily applied to many real-world applications such as our temperature measurement task. PICAXE micros are very easy to program because you don’t need a dedicated programmer – just a serial cable and some free software. This comes in handy if you’d like to prosiliconchip.com.au CON1 9-12V DC PLUGPACK INPUT + A _ +5V REG1 78L05 D1 K IN 1N4004 100nF OUT GND 100F 25V 10F 16V IC1 +5V 100 1 22k CON2 SENSOR INPUT 2 4.7k 270 DQ CON3 SERIAL SOCKET 100 100 3 +5V GND 4 K ZD1 5.6V 1W +V 0V SER IN P0 PICAXE-08M P4 P1 P3 P2 8 7 Q1 BC337 1k 6 B CON4 ALARM C E 5 330 10k GND ALARM OUTPUT A PIEZO A LED1 K PICAXE-08M LED PICAXE-08M BC337 K SC 1 8 0V SERIAL IN 2 7 PIN 0 (OUT0 / SERIAL OUT / INFRAOUT) (IN4 / OUT4 / ADC4) PIN 4 3 6 PIN 1 (IN1 / OUT1 / ADC1) (IN3 / INFRAIN) PIN 3 4 5 PIN 2 (IN2 / OUT2 / ADC2 / PWM2 / TUNE) B E C A 2006 +V 4 8 1 AQUARIUM TEMPERATURE ALARM Fig.1: the circuit diagram reveals a very simple design based around the PICAXE-08M microcontroller. The optional alarm output can be used to trigger an external alarm if you want to make a lot more noise when the programmed temperature limits are exceeded! gram the chip for this project yourself and it also allows changes to be made to the temperature range for different applications. Readers familiar with our previous PICAXE-based projects will immediately recognise the temperature sensor element we’ve chosen – a DS18B20 device from Dallas Semiconductor. These devices provide “direct-to- digital” temperature sensing, which really just means that they’re very easy to use. This is especially true when teamed up with the PICAXE-08M, because it’s BASIC language includes a special command for reading the DS18B20’s temperature. The DS18B20 comes in a TO-92 (3pin) package, which is wired to the end of a 2m-long cable and terminated in a 3.5mm stereo jack. This plugs into a stereo socket (CON2) on the PC board. The DS18B20 is powered from the +5V rail via a 270W resistor, which limits transient current should the device be plugged in with power applied. Temperature data is read from the DS18B20 over the “1-wire” bus, which consists (strangely enough) of just one wire labelled “DQ”. This connects to input4 of the micro via two 100W resistors and a 5.6V zener diode. These The PC board fits inside a small plastic utility case which can be hidden, along with its power supply, in the cupboard beneath the aquarium. siliconchip.com.au SSeptember eptember 2006  75 16090130 270 10k CON3 100 330 K 5 A CON4 100 Q1 BC337 DS18B20 SENSOR INPUT 100 4 8 K LED1 A + 4.7k A CON1 1 IC1 D1 1N4004 K 9-12V DC INPUT ZD1: 5.6V/1W PIEZO 100nF 1k 22k + 100F _ REG1 78L05 PICAXE -08M + ZD1 10F components provide “bullet-proof” antistatic protection for the PICAXE input port – an important consideration if our alarm is to provide long and reliable service. As is the usual practice, a piezo transducer connected to output2 produces the noise. A small transistor (Q1) driven from output1 provides the open-collector output for interfacing with an external alarm, while output0 drives a LED. In addition, the output0 and serial input pins are used to program the PICAXE chip via the serial download socket (CON3). These two pins are wired in the conventional manner, with a 22kW series resistor used to limit current into the PICAXE port from the PC’s higher voltage RS232 interface. Power can come from any 9-12V DC source, such as an unregulated DC plugpack. Diode D1 provides reverse polarity protection, after which a 7805 3-terminal regulator (REG1) reduces the input to +5V to feed the circuit. CON2 OUT GND ALARM SERIAL PROGRAMMING INPUT Fig.2: here’s how to put it together. Leave out Q1 and CON4 if you don’t need the external alarm features. The LED can be bent over and positioned so that it will protrude through a matching hole in the end of the case. Take care with the orientation of the two electrolytic capacitors, the diodes, Q1, LED1 and the PICAXE chip. Assembly All the components apart from the temperature sensor mount on a small PC board coded 03109061. Assembly is straightforward and shouldn’t present any particular problems. Following the overlay diagram in Fig.2, begin by installing the resistors and diodes. Insert the two diodes (D1, ZD1) so that their banded (cathode) ends are oriented as shown. Set aside the piezo transducer for now – it must be fitted last. The remaining components can now be installed in any order that you see fit, with attention to the following points: • Take care not to mix up the transistor (Q1), the DS18B20 and regulator (REG1), as they’re supplied Above: the PC board should take less than 30 minutes to assemble. Note that this prototype unit differs slightly from the final version shown in Fig.2. Right: the piezo transducer is secured to the back of the PC board using machine screws and nuts. Table 1: Resistor Colour Codes o o o o o o o o No.   1   1   1   1   1   1   3 76  Silicon Chip Value 22kW 10kW 4.7kW 1kW 330W 270W 100W 4-Band Code (1%) red red orange brown brown black orange brown yellow violet red brown brown black red brown orange orange brown brown red violet brown brown brown black brown brown 5-Band Code (1%) red red black red brown brown black black red brown yellow violet black brown brown brown black black brown brown orange orange black black brown red violet black black brown brown black black black brown siliconchip.com.au in identical packages. Orient their “flat” faces as shown in Fig.2. • The 100mF and 10mF capacitors are polarised devices and must be inserted with their positive leads aligned with the “+” markings on the overlay. • Similarly, the orientation of the 8-pin IC socket is important, so make sure that the notched (pin 1) end is correctly positioned. Don’t plug the PICAXE chip in until after the power supply has been checked out! • Both stereo sockets (CON2 & CON3) have plastic locating pins that must be pushed all the way into matching holes in the PC board. The sockets will sit flush with the PC board surface once these pins are fully engaged. • We mounted our LED vertically with short lead lengths, which makes it invisible when the assembly is fitted in a case. You may prefer to bend the LEDs leads at 90° so that it can protrude through the end of the case, next to the temperature sensor input. Take care with the orientation of the LED – the anode lead is the longer of the two (see Fig.1). The piezo transducer mounts on the opposite (copper) side of the board. Begin by sliding an M2.5 x 10mm screw into each of the transducer’s mounting holes. Wind up a nut on each screw to act as a spacer and then slip the screws into the two centrally located holes on the PC board. Use flat washers and nuts to secure the assembly in place. Finally, trim and strip the transducer’s wires for connection to the designated pads. Note that the red wire goes to the pad marked “+” in Fig.2, while the black wire goes to “-“. Par t s Lis t 1 PC board, code 03109061, 79mm x 47mm 1 UB5 plastic “Jiffy” box (Jaycar HB-6015, Altronics H-0205) 1 2.1mm DC socket (CON1) 2 3.5mm stereo sockets (CON2 & CON3) (MicroZed CON039) 1 30mm piezo transducer (DSE L-7022, Jaycar AB-3440) 1 2-way 5mm/5.08mm terminal block (CON4) (optional) 1 8-pin IC socket 2 M2.5 x 10mm pan head screws 2 M2.5 flat washers 4 M2.5 nuts 1.5mm heatshrink tubing 1 3.5mm stereo jack 1 2m-length of 3-core data cable 1 probe housing – see text Neutral cure silicon sealant Semiconductors 1 PICAXE-08M microcontroller (IC1) (MicroZed AXE007M) 1 DS18B20 temperature sensor (MicroZed DS18B20) 1 78L05 +5V regulator (REG1) 1 1N4004 diode (D1) 1 5.6V 1W zener diode (ZD1) 1 BC337 transistor (Q1) (optional) 1 3mm red LED (LED1) Fig.3: the DS18B20 is soldered to the end of a 3-core cable and sealed off inside a tube to prevent water ingress. Follow this basic connection diagram, keeping cable length to 2m or less. Be sure to test the sensor before applying the sealant! Making the probe To make the temperature probe, you’ll need a DS18B20 sensor, a 100nF capacitor, about 2m (maximum) of flexible, light-duty 3-core data cable (or similar), a length of 1.5mm heatshrink tubing and some neutral-cure silicone sealant. A small tube measuring 40-60mm in length is also required to house the sensor. We cut down the barrel of a “BIC” brand ballpoint pen for the job. Thin-walled stainless-steel tubing with an inside diameter of 6-8mm would be even better – just make sure that the tube is large enough to accommodate the chosen cable! Start by stripping about 20mm of outer insulation from both ends of the cable. Follow this by stripping 5mm of siliconchip.com.au insulation from all three wires at both ends. Tin the bare copper ends, which can then be trimmed to about 3mm. Choose one end and slip a 10mm length of heatshrink tubing over each wire. Don’t shrink it just yet, though! Next, solder the 100nF capacitor to the +5V and GND leads (ie, the outer leads) of the DS18B20 (see Fig.3) and then solder the prepared wire ends to each of the device’s leads. That done, slide the heatshrink tubing up over the leads, so as to fully insulate each connection, and carefully shrink it in place. Next, pass the other end of the cable through the tube housing and connect it to the jack plug, as depicted in Capacitors 1 100mF 25V PC electrolytic 1 10mF 16V PC electrolytic 2 100nF 50V monolithic ceramic Resistors (0.25W 1%) 1 22kW 1 330W 1 10kW 1 270W 1 4.7kW 3 100W 1 1kW Also required for programming the PICAXE: (1) Serial download cable (MicroZed AXE026) (2) USB-to-serial adapter (only required if your computer lacks a 9-pin serial port) (MicroZed USB010). (3) PICAXE Programming Editor software (available free from www.picaxe.co.uk or order on CD from MicroZed). Note: all parts shown with a MicroZed stock number can be ordered from MicroZed Computers, phone 1300 735 420.You’ll find their website at www.microzed.com.au September 2006  77 The temperature probe can be hidden behind the inlet hose that runs to the water filter unit and secured using a small cable tie. This is the completed unit, together with its temperature probe. You can program it to monitor any temperature range you like (see text), making it suitable for other applications as well. Testing Without the PICAXE micro in its socket or the sensor connected, ap- SILICON CHIP 9-12V DC INPUT 78  Silicon Chip ply power and measure the output of the regulator (REG1). This is easily achieved by connecting your multimeter probes between pins 1 & 8 of the IC socket. If the power supply circuit is working correctly, you should get a reading of 4.75-5.25V. Assuming all is well, disconnect power and insert the PICAXE chip in its socket. Be sure to orient it with its notched (pin 1) end as shown on the overlay diagram (Fig.2). You’re now ready to download the program into the PICAXE chip for testing. Programming The BASIC program shown in List­- TEMPERTURE SENSOR INPUT Fig.3. The assembly is now ready to be sealed but be sure to test it first, as set out below! Once you’re sure that it works, squeeze the sensor’s leads together and coat the assembly generously with silicone sealant. Force as much sealant as possible into the tube just prior to sliding the sensor inside. Finish by forcing additional sealant into both ends of the tube and clean away any excess before leaving it for 48 hours to completely cure. Fig.4: this front panel label can be laminated and attached to the lid using double-side tape. Both the panel and the PC board artwork can also be downloaded (in PDF format) from the SILICON CHIP website. ing 1 must now be downloaded into the PICAXE micro to complete the project. You’ll need a copy of the PICAXE Programming Editor (available free from www.picaxe.co.uk) and a serial download cable (see parts list). Note that the Programming Editor software must be installed on a PC running Windows 9x/Me/2000/XP with a free 9-pin serial port. If your computer lacks a serial port, then a USB-to-serial adapter is also available. The accompanying program can either be typed directly into the Programming Editor or you can download it from the SILICON CHIP website – it’s in a file named Aquarium_Alarm.zip. Once you have the program loaded, connect the serial cable between your PC and the serial connector (CON3) on the alarm PC board. Power up the alarm and hit the “Run” button in the Programming Editor. This will download the program into the PICAXE. If the sensor isn’t connected, the alarm should immediately begin to sound off! Even with the sensor connected, the alarm may sound as soon as power is applied – depending on the ambient temperature. Try gently heating or cooling the sensor to prove that it is working. In some climates, varying the MIN_TEMP and MAX_TEMP values may also prove helpful during testing. Note that it’s good practice to power off the alarm when connecting and disconnecting the sensor. Once you’ve siliconchip.com.au Listing 1: Aquarium Alarm ' Aquarium Alarm v1.0 28/06/06 ' PICAXE-08M ' Define temperature limits symbol MIN_TEMP = 22   'for tropical fish tank symbol MAX_TEMP = 27 ' Pin definitions symbol LED = 0 symbol ALARM_OUT = 1 symbol PIEZO = 2 symbol SENSOR = 4 let dirs = %00000111 main: readtemp SENSOR,b1 if b1 < MIN_TEMP then goto alarm if b1 > MAX_TEMP then goto alarm low ALARM_OUT high LED pause 100 low LED sleep 3 goto main It’s easy to spend several hundred dollars stocking a large tank like this one. Fitting a temperature alarm will help protect your investment. proven that it works, seal the sensor and all exposed connections from exposure to water as described in the “Making The Probe” section. Housing & installation The completed assembly is designed to fit in a UB5-sized plastic “Jiffy” box. Holes will need to be drilled in either end of the case to accommodate the sensor input socket (CON2) and LED and to allow entry of the DC jack. An additional hole will also be needed if you intend to wire up an external alarm system to the open collector output at CON4. Several holes should also be drilled in the underside of the case to let the sound from the piezo transducer out. As always when drilling soft plastics, start with a small pilot hole and gradually increase to the final diameter using several drill sizes. A tapered reamer is handy for finishing off larger holes. Note that as the programming socket (CON3) is intended for use only during project construction, it is set back from the edge of the PC board and cannot be accessed from outside the case – so do not drill a hole for it! Guides integral to the case should siliconchip.com.au wedge the board in place, alleviating the need for mounting screws. If your board isn’t a firm fit in the case, then several blobs of hot-melt glue (or silicone sealant) can be used to fix it in place. The temperature sensor should be positioned so that it is fully immersed in the tank. It can be fastened to existing tubing or a suction cup or two can be used to hold it in place. Other uses The program presented in Listing 1 is extremely simple and its operation self-evident. The upper and lower temperature limits are easily altered, if desired. The project could easily be modified for other, similar applications requiring temperature monitoring. It could even be used for rudimentary control using the transistor output to switch an external device. Operating range of the DS18B20 temperature sensor is -55°C to +125°C. However, care should be exercised when choosing materials for the probe housing and wiring, all of which must be designed to withstand the expected temperatures. Note that we’ve used the readtemp alarm: high ALARM_OUT tune 1,8,($44,$40,$44,$40,$44,$40,$44, $40,$44,$40,$44,$40,$44,$40,$44,$40,$44, $40,$44,$40,$44,$40,$44,$40) goto main command in our program, which returns the temperature as a whole degree. For more demanding applications, experienced programmers may wish to use the readtemp12 command instead to obtain measurements to 0.5°C, as measured by the DS18B20. Refer to the “Humidity.bas” program, published as part of the “PICAXE-18X 4-channel Datalogger” project (JanuaryMarch 2004) for an example of how to use the readtemp12 command. The “Humidity.bas” program can be obtained from the March 2004 download section of our website. You’ll also need the DS18B20 datasheet, available from www.maxim-ic.com If you’d like to know more about PICAXE microcontrollers, you’ll find comprehensive documentation in PDF format at www.picaxe.co.uk. Beginners will also be interested in our “PICAXE In Schools” series, starting in the May 2005 edition. Back issues are available from our subscriptions department (see the subscriptions page SC in this issue). September 2006  79