Update: Home Security Monitoring Prototype


This project is about home security monitoring, but the update is crack for electronics designers. [Simon Ludborzs] continues to work on his prototype and he’s fantastic about sharing his success and failure in a conversational manner.

In April we saw his initial design which combined a SIM900 GSM modem with his own board to let him monitor his home security system without hiring a monthly service. Above you can see a snap of his latest prototype. It’s not fully populated as he’s testing the power supply… which in this state puts out 0V. Obviously that’s not up to his design specification so he started hunting around for the issue. He tells a tale of woe which is near to our hearts. He removed Q6, which is BC807 transistor, in order to test the FET used on the board. This brought it to life and had him looking into the datasheet of the part and its footprint in Altium. The footprint is right, the schematic symbol is wrong. There’s a lucky fix though. Above you can see the original design. The fix was just to rotate the part. This is illustrated as a change in the layout, but it worked with the original pad location. They’re not square to the transistor’s legs but they do still fit the outline.

He goes on to stress test the PSU output and then discuss whether it’s enough for the rest of the project. All in all a fascinating read!

8 thoughts on “Update: Home Security Monitoring Prototype

    1. wizardry is how google manage to kill all it’s products with G+.

      now you have to click a picture on that blogspot page, right click the image when the silly javascript galery shows the resized image, and click to open in a new tab.

      even middle clicks are hijacked. screw google.

    1. I agree, Pablo, as I discovered this myself when trying to figure out why my $400 bench DMM is giving me very strange readings testing this rare new transistor that I dug out of my parts bin…

  1. I had one once that was rotated and mirrored.
    Had to bend the legs backwards (thus mounting the chip upside down) in addition to rotating it.
    Not because of the datasheet though

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