At some time I decided to use the Freescale's
MPR121 Proximity Capacitive Touch Sensor Controller for the keypad at the entrance.
The chip has 0.4mm pin spacing so I decided not to try isolation milling and because of the print size (about 3x4 inches) it would not be cheap to order a finished print. I could use a breakout board - readily available at eBay for a few dollars - but I got stubborn and decided to etch my own print.
I ordered
photo sensitive PCB from Reichelt and found out that I had to illuminate the board for about 25 minutes with the lamp I used. I got stubborn again and started building a UV-LED based PCB lamp. It took to long - and I am not quite done - but today I produced the print I needed. Now I only need to illuminate the board for 40 seconds ;-)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVCg2iclZ2BpnDj6YA4IWSi2MaC1u0oowa_hHwvAzlCmkvITPYFy8dp0ib5PL7XQqS4w4b_oMi-1CbDwhP7mDdE44lIFepZ4GeUb4VtrNkQSL9ui1VkOJD6mt5sLmG1lVBDug_ZU94vZo/s640/IMG_8301.JPG) |
Large pads because it will be placed behind a 6mm board. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWBUXJGf8F1lCwikgxYgIrRlQ0c-Knz8RNIzZ42Px1Ik6gewPY7MBmOZhS5LTP6d8IbsCpuIBYLUma9S35wtT4XhVoGAmg3_CzWRfn5BpfhyHQFUxWVemKftYjiFnn_oUhuUPT7ieph-8/s640/IMG_8302.JPG) |
Traces from the pads back to the MPR121 chip on the reverse. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivaMjfy3av4MMHLOpsXIUimj1kgHHkVWKzcUvPOb0FKL3WahehR77GRV1f62j-inKMEpYGk9nY60cTb6CC4xa8fdJQvroK_divzVbFp89zV8szabQEybaJPWAGCRQ_Ow1gf1RVcshi3o0/s640/IMG_8307.JPG) |
Close up of the area where the chip is to be mounted. |
Next week I hope to solder the chip and test the board.
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