Building an Intrusion alarm part 4: disaster strucks.

I completed the projectbox yesterday. It is looking good (well good enough) and I was eager to wrap-up the project. Just a few solder joints and it was finished. Before I started soldering, as I final test, I screwed the circuit board in the box and plugged in the power, I opened the magnetic sensor and… nothing happened, at least no audible sound either from the relay or the loudspeaker. I checked the voltage on the noise making part of the circuit, nothing. Then I checked the relay part. I measured voltage but the relay will not energize. Probably something has happened when I screwed the circuit board. Now I’m stuck with a nearly finished projectbox and an apparently broken circuit.

When frustration builds up I have learned to leave a project alone. You might end up throwing the project out of the window. On the up-side this may be a learning opportunity. On page 139 of Make:Electronics is an explanation how to trace faults in a circuit. I had no need for that until now. It is also an opportunity to use the minigrabber (see Figure 3-6 of the book) that I had recently bought.

Inside of the finished project box. On the lid two leds, switch, loudspeaker and banana plugs. On the left side the connector for the power.
Exterior of the finished project box
The minigrabbers. Hopefully they will be helpful to find the fault in the circuit

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