Sunday, June 5, 2016

Making a case for an eBay transistor tester

Quite some time ago I purchased a transistor tester from eBay. The device is based on the AVR transistor tester project originally by Markus Frejek, and further developed by Karl-Heinz K├╝bbeler. There are several varieties of these devices for purchase on eBay, and I went with basically the cheapest version available. Despite of this, it seems to work very well.

Figure 1: The transistor tester.
As seen in Figure 1, it is just the bare PCB with no case, and even the display is almost hanging loose. I originally bought the item basically as a curiosity, but I find myself using it quite often. For this reason I think it deserves a case.

Recently I took some time to make my CNC router operational again (perhaps I'll post about this in the future), and what better way to make the case than mill it out of wood :-). I had some black alder stock left over from our sauna renovation, which was of suitable thickness and width. So I fired up the CAD and started drawing.
Figure 2: The case design.
There is nothing special with the design. It has a lot of the material cut out to fit the board and the 9V battery used to power it, and has a lip around the cut out to rise the board at a suitable height for a possible cover plate, which I haven't done yet. I exported the projected geometry to the CAM and produced tool paths.

Figure 3: Projected geometry imported.
Figure 4: Tool paths for a 6mm straight cutter.

I then cut the piece out on the CNC router, where everything went smoothly. The tooling left a 3mm round over in the inside corners, which - in order to fit the PCB - I had to remove manually with a chisel.

Figure 5: Good enough.
Figure 6: PCB and battery fitted in the case.
I still need to cut a cover plate over the case from aluminum, but even before that this case makes using and storing the tester much easier.

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