Wednesday, November 23, 2011

Variable intermittent wiper control - printed circuit board

Finally got around to making a PCB for the wiper control. Used DesignSpark PCB to draw the schematic and PCB layout. The board is 3 x 3.5 inches and was exposed to fluorescent light for 70 seconds. Vertical distance of the two 11-watt Toshiba compact fluorescent lamps from the board was 3 inches. On the long sides, I placed cardboard on which aluminum foil had been taped to reflect light back into the exposure area and even out the lighting. (Up to now I have no idea whether the board is sensitive only to UV or UV + visible light, nor do I know to what degree aluminum reflects/absorbs UV.) Details of the procedure and materials I use can be found in Making PCBs using presensitized boards.

I introduced one modification to the June 2011 circuit. The wire length from the board to the push button (a tact switch epoxied to the end of the stem switch that controls the headlights and turn signal lights) is almost a meter in length, so instead of directly connecting it to one of the MCU pins, I am now using a KB817 optoisolator. I also added a red LED to the circuit. It's connected to one of the MCU pins via a current limiting 330-ohm resistor. Right now it serves no function. I just included it just in case and since the MCU pin is unused.

The Sonalert buzzer isn't in the pics because it's connected via the terminal blocks.

As always the soldering leaves much to be desired. I particularly had trouble soldering the huge pins of the Telemecanique RXM2 DPDT relay to the board. The trick, which I learned only after botching it, is to lay on lots of flux paste on the pins (and copper pads) and melt a huge blob of solder to the puny 30W soldering iron (30-year old, non temperature controlled, and directly plugged into the 220VAC outlet). The thermal mass of the gob of solder and large contact area coupled with the cleaning action of the flux greatly increases the chances of successfully and cleanly soldering these gargantuan pins.

1 comment:

  1. Wow! That's great i hope its work proper and i will also try to design circuit for it.