In message PICLIST@MITVMA.MIT.EDU writes: > Maybe this can solve my problem, i need the ADC and a couple of op-amp to > convert current change, in a line, to data. The DAC is used to subtract > the idle current in the line. Maybe this is a little confusing. > The speed of the DAC isn't very important but it needs to be very stable, > the PWM and the integrator can do that ? I can't comment on the particular PWM in the PIC, but this filtered PWM is commonly used for the tuning circuits in almost all modern TV's. The PWM output from the processor is fed via a resistor to the base of an NPN transistor, the collector of which goes via a resistor to a special 33 volt 'super zener' usually a ZTK33B. This generates a 33 volt squarewave on the collector of the transistor, the amplitude of which is very stable as these ZTK's are very good. From the collector it's fed via two or three stages of low-pass filtering (just series resistors and capacitors to ground) and on to the tuning pin of the tuner. I've had meter's and scope's on these tuning rails many times, and the voltage on the tuning pin is remarkably stable and has no visible ripple. Even with the AFC turned off, the voltage remains constant during my full working day. As long as have a suitable stable HT, you should be OK. Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : nigelg@lpilsley.demon.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.demon.co.uk | | Chesterfield | | | England | | \--------------------------------------------------------------/