{"id":410,"date":"2015-03-03T20:46:27","date_gmt":"2015-03-03T19:46:27","guid":{"rendered":"http:\/\/michalu.eu\/wordpress\/?p=410"},"modified":"2015-04-27T10:10:31","modified_gmt":"2015-04-27T08:10:31","slug":"digital-thermometer-based-on-arduino-with-4-digit-7-segment-display","status":"publish","type":"post","link":"https:\/\/michalu.eu\/wordpress\/digital-thermometer-based-on-arduino-with-4-digit-7-segment-display\/","title":{"rendered":"Digital thermometer based on Arduino with 4 digit 7 segment display"},"content":{"rendered":"

\"DSC01199\"<\/a><\/p>\n

1 x Arduino<\/strong> (in my case it was Arduino Mega 2560 rev2)
\n1 x PCF8574<\/strong> expander
\n1 x 4 digit display with common anode<\/strong> (my was FJ-5461BH)
\n1 x temperature sensor MCP9700AE<\/strong>
\n8 x 220 Ohm resistors<\/strong>
\nsome connectors<\/p>\n

If you want to build your own simple digital thermometer just for fun, this tutorial is for you. All the “ingredients” you can buy on ebay, aliexpress or in your local electronic shop. The temperature sensor can be replaced with other one, but you need to discover\u00a0how to connect it to the rest (especially check the operating voltage and pins). Different will be also way to calculate temperature basing on the output voltage.<\/p>\n

For my sensor MCP9700AE it is:<\/p>\n

float getTemp() {\r\nfloat temp = 0.0;\r\ntemp = analogRead(A0) * 5 \/ 1024.0;\r\ntemp = temp - 0.5;\r\ntemp = temp \/ 0.01;\r\nreturn temp;\r\n}<\/pre>\n
Our simple thermometer display the temperature on 7 segment display. There are many displays on the market, but after you bought any you need to ensure how it works (it means: what pins you should use to control digit and which controls the segments).<\/p>\n
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FJ5461BH<\/figcaption><\/figure>\n
Why I used the expander? The expander simplified process of communication with display and reduced number of connectors. To control PCF8574 you should use very useful library PCF8574.h (you can download it here <\/a>and after that you should import the library to your Arduino IDE)<\/p>\n
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PCF8574<\/figcaption><\/figure>\n
Connect your segments to pins P0-P7 (remember about resistors – red LED should be powered with 2-2.3 V)
\nA0-A2 to GND
\nVCC – 5V
\nGND to GND in your Arduino on somewhere where you have GND \ud83d\ude42
\nSDA, SCL we will use to control segments, but only one thing we need to do is to connect to good pins on your Arduino (marked SDA, SCL).<\/p>\n
Output of the temperature sensor I connected to A0 port.<\/p>\n
Below you will find a short YouTube clip and whole code with comments.<\/p>\n
P.S. My first digit is damaged – \u00a0that’s why I used only three digit to show temperature \ud83d\ude09
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