Looking for advice on how I can trigger a sound FX board from a motion sensor

Thread Starter


Joined Jan 13, 2016
Hello there,

I am fairly new to the world of circuitry and wondered if anybody on here would be kind enough to offer there expertise with my project. I work closely with an animal rescue centre here in the UK, and as part of the walk around their educational area they have some outdoor Dinosaur features :D

I want to create a circuit where a PIR sensor is connected to a sound FX board. When it detects any motion it will turn the circuit on and play the sound (A dinosaur Roar). I am open to other ideas and ways I can achieve this if it means doing away with any of the components I already have...I am all ears :D

So the set up I have at the minute is to try and trigger the power to the whole board. I have linked the audio pins together so as soon as the board turns on, the audio is triggered and looped until the board loses power. It would however be nice if I was able to use a motion sensor to trigger the actual audio banks on the sound board rather than triggering the power to it? I wonder if thats possible.

Here are the components that I have to achieve this and the circuit that I currently have now (Picture Attached) Please note I am no expert and my schematic is terrible. The issue at the minute is, there is a constant hissing noise coming from the board and it is just not powering up fully. I wonder if it has enough power going to it?

Main components:
- Adafruit Sound Fx Board (https://www.adafruit.com/product/2217)
- Adafruit PIR Sensor (https://www.adafruit.com/product/189)
- 1 X Speaker (http://www.maplin.co.uk/p/3w-mylar-square-speakers-77mm-vc88v)
- 4 X AA batteries in a battery pack

I have already installed one of these sound boards within the sanctuary but that just uses a simple push button to trigger the sound from the board. This works great and the speakers are really loud and clear. Im not going to lie, I thought this idea would just be a case of replacing the push button with the PIR sensor to trigger it :( Looks like I was wrong.

Paul H


DNA Robotics

Joined Jun 13, 2014
PIR Output:Digital pulse high (3V) when triggered (motion detected) digital low when idle (no motion detected).

FX Basic Trigger- name the file Tnn.WAV or Tnn.OGG to have the audio file play when the matching trigger pin nn is connected to ground momentarily

I would use an Opto-Isolator chip to ground the trigger pin.

Opto isolator.jpg


Joined Jan 15, 2015
I would use an opto coupler also. That or let the sensor signal which goes high on detect drive a simple transistor like a 2N2222 or similar.



Joined Apr 1, 2018
The noise you heard is either because the PIR output doesn't just turn on and off at low frequency, but has lots of high frequency short period pulses, or because the output does not reach the supply voltage.

If the former is correct, the isolation circuits may not get rid of the noise. In that case you will need a low pass RC audio filter and either a trigger with hysteresis or a one-shot. A 555 can do either, or both.


Joined Apr 1, 2018
"To enable this trigger, name the file Tnn.WAV or Tnn.OGG where nn is the trigger #. For example, if you want to use pin #0, the file could be called T00.WAV (that's two zeros after the T), if you want to use pin #6, T06.OGG - all the way up to T10.WAV"

P.S. If you go with the opto-isolator design then it isn't really isolated if the two ground symbols are identical and connected. The left half of the isolator should only connect to the PIR and the right half only connect to the sound card.

If everything is together and uses the same 5.5 volt USB power supply, then there is no need for isolation, but you still need a resistor/transistor to translate the voltage.


Joined Jan 15, 2015
June 2nd 2017 is when the original poster was seen, so getting close to a year ago. I would guess the problem was solved by now as he or she never returned. :)