Wednesday, 24 April 2013

Working UV controller (sort of)

After making a PCB and finding that it didn't work, and then making up a breadboard version of the circuit and making it work, we're back to making a PCB version of the UV controller circuit - and hoping that it works this time!

Here's a new controller PCB with some simplified firmware on it, simply writing a message to the character LCD. With a bit of jiggery-pokery we managed to get the display to work on our new PCB.

Wiring up the rest of the circuit and putting it on it's own dedicated power supply (running it off a little PIC programmer isn't going to be a good idea if all these LEDs suddenly spring into life!) and everything is still working fine:

The only problem now, of course, is we're running simplified firmware which just writes "Hello" onto the character LCD - the darlington arrays aren't being set so random lines of UV LEDs currently light up each time the circuit is powered up.

But it's encouraging to see that the whole thing still (appears to be) working. Even with a couple of rows of LEDs lit (we'll only ever have one row lit at any one time, and strobe them quickly using PWM to control the brightness) the message on screen remains the same, and we put a start-up sequence in place so that we could see if the PIC is rebooting. It's possible that when a row of LEDs lights up it might create a dip in the voltage supply and reset the microcontroller. A few smoothing caps on the supply line(s) - you can see one on the supply to the LCD in the photo above) and everything is good - no mcu resetting, no ripples, nothing.

So in theory all that remains is to put the "proper" firmware onto the PIC and shove the whole lot into an box and we're ready to try creating our own miniature silkscreen for PCB printing....