I am designing a PIR sensor circuit to detect human movement. I am supposed to display movement using an oscilloscope (the response from this PIR sensor.)

I have used the following circuit but it does not show any response on the oscilloscope.

Is there anything that I need to add?

enter image description here

  • \$\begingroup\$ Please post specifications/datasheet for the PIR Sensor, there are many types. \$\endgroup\$
    – Mattman944
    Nov 15, 2023 at 13:34
  • \$\begingroup\$ It is PIR sensor MURATA IRA-S210ST01 \$\endgroup\$
    – user355274
    Nov 15, 2023 at 13:49
  • \$\begingroup\$ The common mode input range of the 741 doesn't go down to the negative rail. Trash this design and use at a minimum an LM324. One section to amplify, another to compare. \$\endgroup\$
    – Mattman944
    Nov 15, 2023 at 14:09
  • \$\begingroup\$ With your scope on pin 2 and ground on pin 3 of the PIR. Set the scope to a sensitive setting. Wave something really hot in front, like a soldering iron. \$\endgroup\$
    – Mattman944
    Nov 15, 2023 at 14:11
  • 1
    \$\begingroup\$ Mandatory read on 741: electronics.stackexchange.com/questions/304521/… \$\endgroup\$
    – winny
    Nov 15, 2023 at 14:27

1 Answer 1


As in the comments the 741 op-amp is not one of the better choices.
Consider using one of the test circuit configurations in the IRA-S210ST01 datasheet, these also use an op-amp similar to that recommended in the comments.

For additional info you can refer to this application sheet. The document also includes a prototype starter board that should be available, schematic included.

In your original circuit you are using the transistor as a switch rather than a linear amplifier. If you want to view an amplified analog output try using one of the the circuits in the datasheet or application sheet to start.

Since the LM224 op-amp (and similar versions) have multiple parts in one package you can implement an analog stage, a filtering stage, and a comparator stage. Below is one of the test circuits from the datasheet.

Test circuit

(From Murata datasheet Fig. 5)

  • \$\begingroup\$ Thank you it is working perfectly but is there anyway to reduce the SNR \$\endgroup\$
    – user355274
    Nov 16, 2023 at 11:48
  • \$\begingroup\$ What is the pictured test circuit supposed to do? \$\endgroup\$
    – cornelius
    Jan 13 at 10:51
  • \$\begingroup\$ @cornelius - The circuit above only outputs a buffered analog signal from the sensor. The signal can be further amplified, filtered, and sent to a comparator if needed. For more info see the original question above and the Murata datasheet link just below the circuit. \$\endgroup\$
    – Nedd
    Jan 14 at 23:41

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