Re: PIC / PICAXE-controlled LED Beat flasher


"Johnno" <cppjohn@xxxxxxxxxxx> wrote in message
news:1172049223.613368.179260@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Thanks again, although I need to be able to independently control 30
different LEDs. Either I didn't explain this clearly .. or.. do AVRs
really support 30 seperate outputs? (By bank I simply mean a group of
partiular coloured LEDs, I did not mean for this to cause confusion :P

Cheers
John


If you use one of the 40 pin AVRs, you could most certainly get 30
individual outputs (the chips have 4 ports of 8 bits each), but for a 3 bank
application, you are better off using one bit to drive one mosfet (I
recommend the International Rectifier HEXFET) for each bank.. if you have a
12v supply voltage available, run your LEDs for each bank in series with a
current limiting resistor between the LED chain and the power supply.. hook
the other end of the chain to the HEXFET, which will connect the LEDs to
ground when commanded to do so by the microcontroller.

If you dont have 12v available, or if you are using LEDs with a high forward
voltage drop, run them in parallel with a limit resistor for each LED.

The LEDs that we used for the light bar had a drop of about 1.7v and we had
6 per bank... needed about 10 volts.. so we ran them in series with a limit
resistor off the unregulated 12v car voltage and it kept the wiring simple
:) (limit resistor was computed for a 14v power supply to make sure any
spikes from the car didnt blow the LEDs, at the cost of a little brightness
when the voltage was lower)


.

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