I am in first year of Engineering school and I was given an assignment which contains this circuit which drives pressure sensors in a pitot tube :

enter image description here

For training, I am trying to reproduce it using the gEDA free software, but I came accross those little beasts named A1 and A2 I can't reproduce.

What are they ?

[as an aside, does anyone have an idea about which piece of software could have produced this image ? ]

  • 4
    \$\begingroup\$ Potentiometers. \$\endgroup\$
    – brhans
    Apr 27, 2016 at 19:09
  • \$\begingroup\$ why would there be potentiometers in such a circuit ??? :( \$\endgroup\$
    – Magix
    Apr 27, 2016 at 19:15

2 Answers 2


enter image description here

A1 and A2 are potentiometers. (This diagram uses the European notation.)

This diagram could have been drawn in a general-purpose (not specialized for electrical engineering) diagramming tool such as MS Visio. It was not drawn in Altium, or Eagle, or OrCAD.


why would there be potentiometers in such a circuit ??? :(

Potentiometers are there to make adjustments. A1 acts as a adjustable voltage divider (together with R16); it scales the output of OpAmp III. A2 acts as an adjustable voltage divider; it scales the output of the OpAmp IV.

[As an aside, I wouldn't design this circuit the way they did. I would use instrumentation amplifiers (InAmp). I wold guess that the original designers had a goal that the circuit could be made with components that are cheap and available the world over.]


It appears to be a circuit diagram from France. The notation CAPT1 and CAPT2 means Capteur or Sensor. AFF means Affiche or Display. POT A1 appears to be calibrating or balancing the output of the 2 sensors. POT A2 appears to adjust the output level going into the display unit. This of course is an educated guess as it has been a while since I worked with stuff like this.


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