I have a basic one-shot timer circuit (shown below in schematic). If I press the button, it brings pin 2 low and triggers the timer one time for a period which with my cap is about 5 seconds.

Use IR Sensor To Drive Trigger Low

What I'd like to do now is replace the pushbutton with a specific IR sensor which I have. I got it from AdaFruit and you can see the details at: https://learn.adafruit.com/ir-sensor/testing-an-ir-sensor

This particular IR sensor has 3 pins. You supply 5 volts on pin 3, ground on pin 2 and then when you fire the IR remote at the sensor it says that pin 1 is driven low. I have successfully created the circuit which will light an LED with that circuit also -- you can see that circuit below (it's an image from the adafruit site).

How Do I Use This Circuit? How can I hook this second circuit into my first one so that it will replace the push button and drive the trigger low?

Will I need to implement some kind of gate using a transistor?


simulate this circuit – Schematic created using CircuitLab

IR Sensor circuit

  • 1
    \$\begingroup\$ Your schematic has a mistake in that there is a direct connection to both *Reset and *Trigger and direct to +9 V. You need to fix that to make anything work. \$\endgroup\$ Nov 6, 2017 at 4:46
  • \$\begingroup\$ Thanks I will check that. it works in reality but I may have drawn the schematic incorrectly. I will check and change appropriately. \$\endgroup\$
    – raddevus
    Nov 6, 2017 at 5:14

1 Answer 1


The 9 V supply is problematic since the IR Rx is limited to a 5.5 V maximum supply.

Note: You also show the IR RX connected to 6 V on your breadboard ...this may damage it.

If you alter the schematic to that shown below, lowering the voltage to a more acceptable level, it should work.
You could use either 3*1.5 V cells or a single Li-Ion cell providing you don't have a high voltage LED on the output.

enter image description here

I'm not quite sure from your question what result you want, but the output of the IR Rx will be a string of detected IR pulses from an IR remote. The output signal will repetitively re-trigger the 555 monostable, so the LED will likely come on for longer than you think.
If all you are looking for is an indicator of remote activity then this may be ok.

  • \$\begingroup\$ This is very good. I was wondering about the 9v driving voltage on the circuit myself. I will try this as soon as possible and let you know how it works for me. Also, thanks for mentioning that the IR sensor output will pulse like that and trigger multiple times. Good points to keep in mind. \$\endgroup\$
    – raddevus
    Nov 6, 2017 at 5:12
  • \$\begingroup\$ I finally got to build the circuit tonight. I had the .1mF cap on the IR sensor incorrect at first, but then I fixed it and it works fine now. Thanks again for the time you took to draw this out. \$\endgroup\$
    – raddevus
    Nov 7, 2017 at 4:07
  • \$\begingroup\$ FYI - I read over the 555 timer datasheet (ti.com/lit/ds/symlink/lm555.pdf) & came across (monostable): "During the timing cycle when the output is high, the further application of a trigger pulse will not effect the circuit so long as the trigger input is returned high at least 10 μs before the end of the timing interval. However the circuit can be reset during this time by the application of a negative pulse to the reset terminal (pin 4). Output will then remain in the low state until a trigger pulse is again applied." Mine stays high for over 5 seconds so no re-trigger problem. \$\endgroup\$
    – raddevus
    Nov 8, 2017 at 14:16

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