Qball's Weblog

Domotica box v2.1

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Don’t ask me how, but I managed to break the usb break out board of my RFID receiver. (I hid it in a corner under the table, and after moving something under the table, it got hit..)

So I decided to ditch the whole usb break out box and wire it directly to the expansion header of the panda-board.

The RFID reader uses 5V power (available on the panda-board) and a simple RS232 interface (9600 8N1) at TTL level.
Because the panda-board uses 1.8V I/O I could not directly hook this up. I decided to build a level shifter using 2 transistors.
After hooking this up, everything worked, and then I realized I probly had enough (because I only needed RX on the pandaboard) to just use 2 resistors to drop the voltage level.
So after making a small print with 2 resistors, I managed to build in the RFID reader directly in the box, connected to the 4th UART on the expansion header.

This had a nice side effect, it allowed me to remove the USB hub, reducing the power consumption of the domotica box with almost 20%. (3.2W before, 2.6W after). Yes, the sitecom hub was trying to mimmick a space-heater.

New image (the RF is in the middle bottom)

Inside (with RFID)

As you can see I used ‘kneading adhesive’ to stick everything to the side and top, I am not happy with this (no idea how well this will last).
I need to find a good solution for this (that still allows me to modify stuff easily), because if something would let loose, and cause a short would be shamefull. (I tried to place things so it won’t be a real problem.