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Make a motion activated message playback module.
June 3, 2011

We now carry a motion activated module that is pre-assembled and you can see it at this link: Motion activated playback module 

A few weeks ago a customer asked me about building a motion activated switch that could play a message when someone walked past. Because this wasn't the first time someone had asked me for this, I went busy to work out a solution. At first I was just going to use an Arduino and code up a solution, but as I thought about it a simpler solution presented itself. I grabbed a few of our kits from the self and started splicing them together. The result was quite satisfying. 

The base of the project is a recording module. In this situation I used our USB5M 300 Second USB recording module, but any of the following will work with some simple wiring changes:

Or get our new USB6M+PIR here which has a light sensor and PIR ready to plug in!

After you get a message on your recorder, you can set it aside and move on to the next step.

The next component in the module is the PIR. A PIR or Passive Infrared detector measures infrared light radiation from an object in its field of view. Since living things naturally give off infrared radiation, the PIR will detect a passing person. This will also work with dogs, cats, or anything else that is living and of substantial size, (most insects are excluded). The PIR I chose was the CPS76. I picked it because of its small size, relatively simple operation, and it has a really neat "start up" delay that prevents it from triggering in the first 25 seconds. 

Now, I have the sound recorder and my PIR but there is still a major problem. The playback module uses a simple normally open momentary switch to activate. The PIR's output is a digital high-low signal. These two interfaces are incompatible. Fortunately for the electronics hobbyist, we have a solution. The CPS156 is dual channel HI /LO switch. Basically it takes a HI / LO digital signal, processes it, and then decides whether or not to switch a mechanical switch (relay). I assembled a CPS156 (which only took about 15 minutes) and now I was ready to bring everything together. 

The wiring is relatively simple and because the CPS156 and CPS76 use the same voltage, they can operate off of the same power supply. Above is a wiring diagram and below are some pictures of the finished product.

The PIR only has three connection that need attached and they are relatively straight forward. The recording module will likely have a "play" button attached via two wires. You will need to cut the two wires and remove the button. These two wires will then attach to the relay output on the CPS156. Once everything is wired up attach your power supply. You will notice that for the first 25-30 seconds nothing happens. This is the start up delay. After the startup delay is complete, walking past the PIR will activate the relay and play the message back.

-Tanner Ewing
VP of Engineering