On Sun, 13 Jul 2003 08:24:13 +1000, you wrote: > --- Mike Harrison wrote: > On Sun, 13 Jul 2003 = 06:47:45 >+1000, you wrote: >> >> >thankz guys - u gave me a lotta good ideas. i've half breadboarded a = test >> cct - >> >will use the PIC to drive a 4N25 opto coupler so it has to be active = low to >> >fire. >> >> An optoisolator will not give any advantage over a simple resistor in = this >> application. > Dang, won't it? the PIC's at 5V & the transistors are at 12V ... ? How = would u >configure it? View with fixed-pitch font, e.g. Courier : | | +--LED--LED--LED--LED--Rs--+ | | = d|--+-LED--LED--LED--LED--Rs---+---R2--- +12V | | Pic output --100R---C1---+----+----| N-Ch logic-level Mosfet | | | | | | | s|-+ C2 R1 D | | | | | | --------------+----+------+---------------------------+--0V R1,C1 chosen to limit 'on' pulse length, R1 also ensures output is off if= PIC pin floats. Maybe something like 100nF/1M? C1 needs to be large compared to Mosfet's= gate capacitance. D is a diode with Anode to ground, to clamp the capacitor voltage when = the PIC pin goes low the 100R series resistor limits slew-rate in conjunction with the = Mosfet's gate capacitance and also limits peak current from the PIC pin. C2 supplies the peak power for the LEDs, and in conjunction with R2 = limits the surges seen by the supply The number of LEDs you connect in the series chains should be chosen to = keep the dissipation in Rs reasonably low, while allowing enough headroom to kee Led current = variation acceptable with variations in supply and variations of LED forward voltage with = temperature and part-to-part differences. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics