Saturday, October 25, 2014

Short wires

Here is what happens when you try to connect PIR sensors to powered up main board :(. Well not really what should normally happen.

I was about to test everything in real life as the software and hardware worked fine together, but didn’t think about short wires on the other ends. I have connected 2 PIR sensors and left the board powered on. All the leds on GSM modem a Ethernet card lit up and I started to connect wires on first PIR that is just around corner. When I went back to main board there was strange light coming out of place where is no led. It was bead!  But before I was able to unplug it it died and took some other components with it. The second PIR had shorted power wires, upps.

I must say the power supply is too strong, with battery connected it can easily put few amps into any 12V rail. As you can see on the picture the power went to second PIR sensor there was shorted and came back to analogue ground that is connected to digital ground by bead. And it didn’t withstand the power that was flowing through it. As is burned it probably touched the 12V rail that is near and killed the rest of the board. So, yes I have designed the board as well as I could to handle over voltage and or short on signal wires, but I failed on power lines.

Damn, I have the input over current, over voltage on the remote board but not on the main board. A simple polymer fuse would save the board as it was able to operate like this for at least 3-4 minutes. Now I have to think if I will make new revision of the main board or just solder another one and put a fuse on the 12V input.

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