as i cant get a digital pot grr: @ maplin) i was thinking bout using a binary up down counter and a bin > dec decoder with optoisolators on each output and a bunch of resistors so that for each decimal value you have a higher or lower speed would this work and can you simplify the idea? ill probably do a diag when i get home got to go to maths lecture now :-(
There must be some way of using a DAC chip, all you need at the end is a dc voltage between 3v and about 7v, and that can be tweaked to a narrower range (if needed) by reducing the sawtooth amplitude. btw, Rapid do the Dallas 1267 digipots. Catalogue sections now available as pdf files, save you £3.
i did notice that the catalogue was online (might even print it at uni ) but i had completely forgotten that they did digi pots (doh) ne idea how much current the mosfet needs? also theres a couple of downers with the digi pot 1. Vs MAX is 5V which could be sorted out with a little bit of fiddleing so not so bad 2. its serial programmable only not just button for up button for down. oh and its not RS232 either. again this could be sorted out with a pic in 30 secs flat 3. rapid are only selling while stocks last but i could just request samples 4 its 256 state which is a few to many really 5 an 8 bit counter will end up being simpler in the end i think ho hum however the dac08000 DAC looks like the daddy if u ask me linkage to datasheet can output upto 20 v p-p range (can be set to what u need) (with supply of 36v) parallel interface (slap a 4 bit counter ont the 4 msb's is my plan) interface directly with both ttl and cmos (oh and rapid stock it under d-to-a convertors
AFAIK that Vantec Nexus baybus uses a 20-pin µpc and 4 power transistor switches to run 4 channels (with PWM), so there's a thought for you. MOSFETs take a nanosecond or less at around 50mA to charge up & switch, then a few nanoamps to hold on. Limit the current if the 50mA is too much for the driver, it just slows down the switching time a nats. Not a worry at 100Hz. Doing it properly, you use a couple of extra transistors like this:
hmmm *digs out pic programmer* mebbe time i tried this again . . . DOH need to get more pics 1st blown my last 1 up :-/ dont even know how i did it either oh well this circuit will do 4 now cos i only have 3 fans total (okok so ones a delta ) the others r psu and motherboard
