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Try this by Somnath Bera ARDUINO-BASED FRIDGE MONITOR AND DATA LOGGER Monitor the temperature and humidity in your refrigerator (or elsewhere) remotely with this Arduino-based device. It can also log these parameters over time so you can see how much the temperature and humidity vary as the compressor cycles on and off, how often the defrosting cycle occurs, how often the door is opened and so on. T his remote sensor/data logger is based on a minimal Arduinocompatible circuit. As is typical for Arduinos, it uses an Atmel AVR ATmega328 microcontroller. You could use a pre-built Arduino board such as the original Uno, the Freetronics Eleven or the Leostick but the simpler circuit also has the advantage of reducing power consumption and therefore extending battery life. With the specified battery (6 x 2Ah NiMH AA cells), the logger will run for roughly two days continuously. The time, temperature and humidity are shown on a remote backlit LCD which can be up to 100m away from the logger (depending on intervening obstacles, antenna size etc). This data 84  Silicon Chip is also logged to a file on a microSD card every five seconds along with a time stamp. This would be a good project for relative beginners, especially those interested in learning how to use Arduino boards, since it involves relatively few components and uses several pre-built modules. Circuit description There are two circuits for this project. The first, shown in Fig.1, is the sensor/ logger/transmitter unit comprising the ATmega328 micro, AM2302/DHT22 single wire temperature/humidity sensor, 433MHz transmitter and MicroSD module for data storage. A 16MHz crystal is used as the in- struction clock source so the micro can keep time with reasonable accuracy. The AM2302 or DHT22 sensor (TS1) is connected to input pin 5 of IC1 (digital input #3) with a 1kΩ pull-up. The Arduino software decodes the digital signals from this sensor to get the temperature and humidity readings. These are then sent to 433MHz transmitter module TX1 from pin 4 (digital output #2). This data is also periodically logged to the microSD card via breakout board SD1. This is driven from IC1’s SPI interface consisting of pins 16 (slave select), 17 (data; master out, slave in), 18 (data; master in, slave out) and 19 (serial clock). The card detect pin is not used as the card is not normally siliconchip.com.au inserted or removed during operation. 5V S1 100W 100nF 100nF SD cards require a 2.7-3.3V supply and ZD1 BAT1 S2 S3 100mF 5V S1 100W 5.1V 6 x AA 7 20 SET SET the breakout board we 100nF 100nF HOUR MINUTE 5V Vcc AVcc have specified contains 1 28 ZD1 BAT1 PC6/RESET S2 S3 A5 100mF an onboard 3V 150mA 5.1V 6 x AA 7 20 SET SET 2 27 D0/RXD A4 TX15V Vcc regulator which runs HOUR MINUTE 10k Vcc AVcc 26 13 D1/TXD from 5V. We aren’t A3 28 PC6/RESET A5 433MHz 4 25 DATA ANT 2 D2/INT0 using the 3V supply TX A2 27 D0/RXD A4 TX1 Vcc 10k MODULE 5 24 elsewhere so that pin is 3 D3/INT1 A1 26 D1/TXD IC1 A3 433MHz left unconnected. The 6 23 4 D4 ATmega328 A0 25 DATA ANT D2/INT0(Arduino) A2 TX GND breakout board also 11 21 5 D5/PWM 24 5V MODULE AREF D3/INT1 A1 has a 74HC4050 level IC1 3V 5V 12 19 S4 6 D6/PWM 23 CLK SCK/D13 D4 ATmega328 GND A0 shifter IC onboard to HALT Vcc (Arduino) 13 18 1k 11 21 SD1 D7 DO MISO/D12 5V translate the 5V signals D5/PWM AREF TS1 14 17 3VAdaFruit 5V 12 19 S4 from IC1 to a level suitD8 PWM/MOSI/D11 DI AM2302 DATA MicroSD card D6/PWM CLK SCK/D13 HALT or Vcc DHT22 Breakout 16 13 18 able for the SD card (ie, 1k CS PWM/SS/D10 Temperature/ board+ SD1 DO MISO/D12 9 D7 Humidity TS1 Sensor AdaFruit 15 0-3V). Output signals 14 OSC2 X1 PWM/D9 17 D8 PWM/MOSI/D11 DICD MicroSD card AM2302 DATA 16MHz GND from the SD card go or DHT22 Breakout GND 16 10 CS Temperature/ board+ 9 OSC1 PWM/SS/D10 directly to IC1 as its Humidity Sensor OSC2 15 GND PWM/D9 GND X1 CD inputs will sense 3V as 10k 10k 22pF 22pF 16MHz GND 8 22 GND 10 a high level when runOSC1 ning from a 5V supply. GND GND 10k 10k 22pF 22pF The micro’s own Fig.1 (above): circuit for the 8 22 It’s based around a stripped down data logger/transmitter unit. power supply is basic, Arduino in the form of an ATmega328 (IC1). TS1 is used to monitor temperature and humidity using just a 100Ω series and data is transmitted in real-time using 433MHz module TX1. Data is simultaneously logged SD1. resistor and 5.1V zener to the microSD card OUT IN via 5V S1 diode to regulate the GND 100nF 100nF ~7.2-9V supply from REG1 7805 BAT1 IN OUT 470mF the six AA batteries 100mF 6 x AA 5V S1 7 20 RX1 Vcc GND 100nF 100nF to 5V. A 3-terminal Vcc AVcc REG1 7805 1 28 BAT1 regulator could be subPC6/RESET A5 433MHz 470mF 100mF 6 x AA 7 20 DATA ANT 2 27 stituted for reduced opX RX1 RVcc D0/RXD Vcc AVcc A4 MODULE erating current. Switch 26 13 D1/TXD 28 A3 PC6/RESET A5 433MHz S1 turns power to the 2 15 4 25 DATA ANT GND 2 27 RX D2/INT0 A2 D0/RXD BACKLIGHT Vdd A4 circuit on and off. + 5 24 4 MODULE 3 D3/INT1 RS A1 26 CONTRAST D1/TXD IC1 Momentary pushA3 6 6 23 VR1 3 2 15 4 D4 ATmega328 A0 25 GND CONTRAST EN buttons S2 and S3 are D2/INT0(Arduino) A2 LCD MODULE 10k BACKLIGHT Vdd + 11 21 5 5 D5/PWM 24 4 used to set the time for R/W AREF RS D3/INT1 A1 CONTRAST IC1 BACKLIGHT 12 19 logging. The remote GND D7 D6 D5 D4 D3 D2 D1 D0 6 6 D6/PWM 23 VR1 3 – SCK/D13 CONTRAST D4 ATmega328 EN A0 LCD MODULE 10k (Arduino) 1 14 13 12 11 10 9 8 7 16 receiver unit shows 13 18 11 21 5 D7 MISO/D12 R/W D5/PWM AREF the time being trans14 17 LED BACKLIGHT 12 19 GND D7 D6 D5 D4 D3 D2 D1 D0 D8 PWM/MOSI/D11 – 1 D6/PWM SCK/D13 mitted by the logger 16 1 14 13 12 11 10 9 8 7 16 13 18 PWM/SS/D10 D7 l MISO/D12 9 so it’s simply a matter 15 14 OSC2 LED X1 PWM/D9 17 D8 PWM/MOSI/D11 of pressing these but1 16MHz 16 10 tons to increment the PWM/SS/D10 OSC1 l 9 OSC2 15 hour/minute reading GND PWM/D9 GND X1 330W 16MHz until the time on the Fig.2: the receiver circuit. It’s based around the same 8 22 22pF 22pF 10 chip as Fig.1 but with different software. The software OSC1 receiver is correct. The GND GND log entry time stamps receives data from RX1 (that was transmitted by TX1 330W 8 22 on the logger) and displays it on the LCD screen. 22pF 22pF will then be correct. LED1 flashes to indicate valid data reception. Both However note that the units run from a 6 x AA battery pack. date at power-up is hard-coded into the Arduino sketch so the micro will need which log entries for that session are be handy if you are planning to build to be re-programmed each time the written. The temperature and humidity your temperature/humidity logger uslogger is to be used for the date stamps is logged every five seconds. ing an actual Arduino board such as the to be correct. Freetronics Eleven. However it will be Pushbutton S4 is used to halt logging Alternative microSD interface larger and consume more power. and the unit must be power-cycled to SparkFun also make a similar miThe only change necessary to use the resume. Each time the unit powers up, croSD card interface, however it is a SparkFun shield is to connect pins D8 it creates a new file on the SD card to full-sized Arduino shield. This would and D10 together. That’s because the siliconchip.com.au December 2015  85 is flashed to show that valid data has been received. The prototype temperature/humidity sensor and transmitter unit, built on a length of stripboard. Logging other parameters If you wanted to attach other sensors to the Arduino you could do so – it has plenty of spare analog and digital pins. You would have to modify the transmitter “sketch” software, to sample data from the new sensor and include it in the transmitted packets and logfile. You would also need to modify the receiver sketch to decode and display the extra data (unless you simply wanted to log it). We won’t go into great detail on how to do that here but that’s the great thing about systems like Arduino – you can download the source code for this project and modify it as much as you want. If you don’t know how to program an Arduino, there are plenty of books and internet pages that explain how to do so and also internet forums where you can ask questions and get help. Construction circuit is connected directly across the 5V supply while a 10kΩ trimpot provides contrast adjustment by varying the negative bias voltage at pin 3, relative to the positive supply, between 0 and -5V. IC1 waits to receive valid data from RX1 and when it does, it updates the LCD to show the time (as reckoned by the logger), temperature (in degrees Celsius), relative humidity percentage and status. At the same time, LED1 MOSI RESET SCK MISO 86  Silicon Chip 9 10 Receiver unit The receiver unit, (Fig.2) is also based around an ATmega328 microcontroller. The data stream from a 433MHz receiver unit is connected to pin 4 (digital input #2) and the micro drives a 16x2 alphanumeric LCD module (LCD1) in 4-bit mode. It does this via digital outputs D5-D8 (pins 11-14) for data and using digital output #3 (pin 5) to control the reset pin and digital output #4 (pin 6) to control the enable pin. The R/W pin of the LCD module is tied to ground as there’s no need to read data from it. The backlight LED 1 2 SparkFun shield uses D8 as the Card Select pin. D10 is more traditional as this corresponds to the micro’s hardware slave select pin, however in practice any digital I/O can be used for this purpose. Our circuit doesn’t use D8 so joining them should not cause any problems. One advantage of using the SparkFun microSD card shield is that it contains an 11 x 12 prototyping area along with pads to make connections to each of the Arduino pins. Most or all of the required extra components will fit there, making for a neat finish. 100nF GND VCC Fig.3: if you want to program an ATmega328 chip using an in-circuit serial programmer (ICSP), here is how to make an adaptor board. Note the orientation of the 10-way IDC socket which is shown in top view. You may need to add a crystal and load caps between pins 9 & 10 of the IC socket to re-program a chip that has already been programmed (see text). Our prototypes were built on Veroboard using point-to-point wiring – see the adjacent photo. There are various different types of protoboard available including an “IC prototyping board” (which goes under various names) that mimics the connection pattern used on solderless breadboard. That would probably be a good choice for this project although a “donut board” (just copper rings on a 0.1” grid) would work too. Construction for both units is similar. Luckily neither circuit is too complex and most of the “heavy lifting” is done by pre-built modules. In both cases, start by soldering in the socket for IC1. Add the crystal, ceramic capacitors and pull-up/pull-down resistors across the appropriate pins. The next step is to mount the various modules, pushbuttons and switches in convenient locations and then run insulated wires connecting to their pins back to the appropriate IC pins as shown in the relevant circuit diagram. Finally, wire up the power supply and prepare to connect the battery. If you’re basing your unit on a prebuilt Arduino module, construction is a bit easier. If not using the microSD card shield with prototyping area, or for the receiver unit, you can use a prototyping shield which simply plugs into the Arduino board. Like the microSD card shield, these also provide connection siliconchip.com.au Parts list – Arduinobased Temperature/ Humidity Monitor Logger/transmitter unit Here’s the display from the receiver board. Data can also be saved to an SD card for later analysis. pads for the various pins which will be labelled. Programming the chips For an Arduino module, the software (available from www.siliconchip.com. au) can then be uploaded using a USB cable and the free Arduino IDE software from www.arduino.cc/en/Main/ Software In this case you will be compiling and uploading the .ino “sketch” file via the IDE, once you have selected the correct target board and established communications. However if you are building the minimal design you will need an Atmel AVR in-circuit programmer along with a 28-pin programming rig. AVR ICSP adaptors are available from websites like Ali Express and eBay starting at less than $2. Just search for “avr programmer”. You may be supplied with suitable software; if not, use software such as avrdude-gui (http://sourceforge.net/projects/avrdude-gui/) or PonyProg (www.lancos.com/prog.html). You will also need a programming adaptor for the ATmega328. You could use our PIC/AVR Programming Adaptor board from the May and June 2012 issues, or you could build one on a small piece of Veroboard with a 28-pin socket (ideally, ZIF) plus a 2x5 pin header. The required circuit is shown in Fig.3. Note that there are a couple of tricks when programming an AVR using the ICSP method. One, you may need to set the “fuses” as a separate step to uploading the hex file. You can determine the correct fuse settings for your chip to run an Arduino sketch here: www. engbedded.com/fusecalc Secondly, you should set the fuses AFTER uploading the hex file because once you do, the chip will switch to running off the external crystal and siliconchip.com.au unless your programming board has a crystal (and appropriate load caps) or other clock source, you will lose communications with the chip. Our PIC/AVR Programming Adaptor board has a selectable clock source for this sort of situation (see that article for more details) although if using your own adaptor, you could simply solder a crystal and pair of caps to pins 9 and 10 of the socket as shown in Figs.1 & 2. Alternatively, if you don’t have an AVR in-circuit serial programmer, you could get a universal programmer such as the MiniPro TL866CS and use the supplied software. These are available for around $40 on Ali Express and ebay and can program just about any programmable chip including most PICs and AVRs. Powering it up Regardless of how you programmed the chips, plug in the receiver unit chip and switch it on. The LCD backlight should come on but not much else will happen as the transmitter is not running yet. If using the logging functionality, insert a blank microSD card into the receiver unit before switching it on. Once both units are on, after a few seconds you should see a display on the receiver LCD which will update periodically with new temperature and humidity data. You can then use the pushbuttons on the transmitter/logger unit to set the correct time. After that it’s simply a matter of placing the transmitter logger in the fridge or whatever else you want to monitor and observe the readings on the receiver LCD. You can then leave the logger to do its thing, retrieve it later, press S4, switch it off and remove the microSD card to check the logged SC data on a PC. 1 piece Veroboard/protoboard/stripboard 1 28-pin narrow IC socket 1 AdaFruit industries MicroSD card breakout board+ (SD1) OR 1 SparkFun MicroSD shield (SD1) (see text) 1 AM2302 or DHT22 temperature & humidity sensor (TS1) 1 433MHz transmitter module (TX1) 1 172mm length of stiff insulated wire (antenna for TX1) 1 six AA-cell battery holder 1 toggle or slide switch (S1) 3 momentary pushbutton switches (S2S4) 1 16MHz crystal (X1) Semiconductors 1 ATmega328 microcontroller programmed with remote_ datalogger_with_time_set.ino/hex 1 5.1V 1W zener diode (ZD1) Capacitors 1 100µF 16V electrolytic 2 100nF ceramic 2 22pF ceramic Resistors (0.25W, 5%) 3 10kΩ 1 1kΩ 1 100Ω Receiver unit 1 piece Veroboard/protoboard/stripboard 1 28-pin narrow IC socket 1 16x2 alphanumeric backlit LCD module (LCD1) 1 433MHz receiver module (RX1) 1 172mm length of stiff insulated wire (antenna for RX1) 1 six AA-cell battery holder 1 toggle or slide switch (S1) 1 16MHz crystal (X1) Semiconductors 1 ATmega328 microcontroller programmed with fridge_temp_receiver_lcd_with_ data_logger_time_set.ino/hex 1 7805 5V regulator (REG1) 1 LED (LED1) Capacitors 1 470µF 10V electrolytic 1 100µF 16V electrolytic 2 100nF ceramic 2 22pF ceramic Resistors 1 330Ω 0.25W 5% 1 10kΩ trimpot December 2015  87