Sunday, 2 January 2011

It Lives

I programmed the PIC 18F2525 MCU today. I've been working with PICs for a long time and I am fortunate to have a Microchip ICD2 programmer/debugger. I extended the wires from this to allow me to program the MCU on breadboard:

I wanted to attach the LCD module to the RevH board using an IDC connector to minimise soldered connections. This is where I encountered one of several unsatisfactory issues with the Milestag RevH design. The LCD connector has been CADed so that odd and even pins are swapped in relation to IDC connectors.

i.e. Pins 1 & 2 are swapped, pins 3 and 4 are swapped.

This prevents using a female IDC connector at the RevH PCB end and a male one at the LCD end. I was forced to solder the leads to the LCD with the pins swapped.

Once this was done, I powered up the board. I initially thought it was dead as nothing appeared on the display but on closer inspection, the LCD was displaying:


but very faintly. Issue 2 with the Milestag design is that the LCD contrast is set with 2 fixed resistors. This is fine when using the stock Lasertagparts LCD module but I got mine from Ebay priced 2.87UKP including delivery.

The Milestag schematic uses two fixed value resistors to form a potential divider to set the LCD contrast. I had no idea what values were required for my LCD module so I swapped the 17K resistor for a 2.2M pot and tweaked it until I got an acceptable result, then measured the pot resistance which came out at 175K. I upped this to 180K. This really should have had a trimmer on the PCB to simplify this for none stock LCD modules.

And so it lives:

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