Revising the amplifier

A project log for Hakko 907 based Soldering Station

A soldering station based on the easy to source Hakko 907 soldering iron, which is a 24V 50W soldering iron with integrated thermistor.

KuroKuro 04/02/2015 at 10:060 Comments

I've noticed that the temperature sensor amplification could be improved.

Just follow these instructions:

  1. R3 of 10kohm
  2. R4 of 47kohm
  3. R5 of 1kohm

If you want an explanation, keep reading.

The equation for the op. amp. output voltage is given by:

\color{White} \large Vo = GAIN * 5V * \frac{Rsens}{R3 + Rsens}The ideal value for Vo is just below 5V when Rsens is at it's greatest value. Assuming Rsens of 200ohm when hot, calculating for 48x gain and R3 of 10kohm:

That means the max value at the output of the operational amplifier is 4.71V. We could increase this value and that would increase the precision in the temperature readings.