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This is a K-type (or J-Type) thermocouple amplifier which can be used to amplify the tiny voltage from a thermocouple to a higher voltage, readable by a microcontroller. Thermocouples can be used to measure very high temperatures, but they only output a very low voltage, hence the need for this amplifier.
This kit is based upon the AD8495 precision K-type thermocouple amplifier, or the AD8494 J-type version. The board requires a 5V supply and gives a linear output of 5mV per degree C. The circuit board contains filtering for the standard amplifier configuration. It can be used to measure temperatures up to 1000C.
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I had designed and built a temperature controller for a reflow soldering oven which used this thermocouple amplifier. A couple of people asked me about this circuit so I decided to quickly make a simple breakout PCB.
This converter can be used anywhere you need to measure high temperatures – such as soldering temperatures, flue and exhaust gas temperatures, BBQs and ovens.
Below 100C I would generally use a thermistor, but not many thermistors are rated for temperatures above 150C. In that case we need to use a thermocouple which output a tiny voltage. This must be amplified and filtered so that it can be read by the ADC in a micrcontroller.
Buy one here:
This is a relatively simple to put together kit, although it does have one surface mount IC to solder. The kit includes the following parts:
Note: You will need: soldering iron, solder, wire cutters.
The construction instructions are available here:
Here is the circuit schematic:
|P1||Screw Terminals for thermocouple|
|U1||AD8495 SMD K-type thermocouple amplifier|
KiCAD design files
The PCB and schematic for this project were drawn using the open-source KiCAD electronics design package.
Here is the PCB and layout design:
Testing the output
Here the board is set up with a multimeter and hot air gun to heat the thermocouple:
The output voltage is 1.373V, which equates to 1.373V / 5mV = 274C. This could be easily read by the ADC in a microcontroller.