I need a cheap vacuum regulator, so I decided to try to reuse a blood pressure monitor that I have laying around unused. The sensor itself is a simple bridge type and the signal is amplified by an IC which I cannot identify. It seems that the IC is powered by 3.6V - the red arrow on the picture. The two yellow arrows are connected directly to the microcontroller on the other side of the board. I suspected that these are the outputs, but... They have 3.6V when idle, and when the measurement is started the voltage drops to 3.08V and stays there until the measurement is done. It is interesting that this drop happens before the pump is started, so apparently those are not the outputs. I tried to measure the rest of the pins, but I cannot find any that changes its voltage with the change of the pressure. How this is supposed to work?

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  • \$\begingroup\$ try probing the pins on the sensor rather than the IC \$\endgroup\$
    – Neil_UK
    Commented Oct 25, 2023 at 11:38
  • \$\begingroup\$ Try probing with an oscilloscope to see if there's a change in frequency with pressure, rather than voltage. \$\endgroup\$
    – brhans
    Commented Oct 25, 2023 at 11:55
  • \$\begingroup\$ @bhrans - you are correct. I don't know why I was thinking that this is just some kind of operational amplifier. It looks like it has digital interface. So unfortunately I won't be able to use it \$\endgroup\$
    – irilinir
    Commented Oct 25, 2023 at 12:34
  • \$\begingroup\$ Can the sensor measure vacuum anyway? \$\endgroup\$
    – MiNiMe
    Commented Oct 25, 2023 at 12:42
  • \$\begingroup\$ @Neil_UK - the sensor is more or less clear. It is a bridge that provide small voltage difference, which should be amplified because it is around 80mV. The thing is that I wanted to use the amplification part too, but as I saw on the scope, it has digital interface. Without knowing the protocol, I cannot use it. \$\endgroup\$
    – irilinir
    Commented Oct 25, 2023 at 12:44

1 Answer 1


After measuring it with the scope, it appears that the two yellow points are actually a digital interface (103 seems like a pullup resistor). Since I cannot identify the IC, I won't be able to use it.


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