Russell, Is less than 50 cents low cost enough? I have built analog to pwm circuits as follows: 555 timer is used in astable mode with 50% duty cycle. The voltage across the timing capacitor is fed to one input of a comparator. The analog control voltage is fed to the other input of the comparator. PWM output is taken from output of comparator. Note that the 0-100% range corresponds to voltages from 1/3 Vcc to 2/3 Vcc. Output from the comparator is 0% to 100% pwm signal. Reversing inputs to comparator results in 100% to 0% pwm signal. An opamp can be configured as a signal converter to take the desired input range and convert it to the 1/3 to 2/3 Vcc range needed to match the 555 timing capacitor waveform. PWM is independent of the 555 operating frequency. Even though the timing capacitor waveform is a sawtooth (and not a ramp or triangle) wave, the + and - slope waveforms are reversed in such a way that the output linearity of the resulting pwm wave is very close to that obtained with a linear ramp. If using a potentiometer to manually generate the reference voltage for the comparator, simply choose a series combination such as Vcc connected to a 10k resistor, connected to a 10k pot, connected to a 10k resistor connected to ground. Note that MANY comparators can share the same timing capacitor waveform at once. A 555 circuit and a quad comparator would give you 4 independently controllable analog to pwm outputs. Is that low-cost enough per pwm? If you have a bipolar power supply, the 555 circuit can be replaced by a single comparator, two resistors and a capacitor. Output of opamp connects to resistor and capacitor in series to ground. Resistor/capacitor node connects to (-) inverting input. Output also connects to two resistors in series to ground. The node of the two resistors connects to the (+) non-inverting input. This comprises a bilaterally symmetrical square wave generator with 50% duty cycle. The capacitor waveform will be a sawtooth. As before, this sawtooth wave can go to more than one comparator to provide pwm outputs. Note that in this case signals are all bipolar. One quad comparator (opamp) can provide three independent pwm outputs (plus the sawtooth waveform.) If you only need a single pwm output, a dual comparator will do it all. The few resistors and the capacitor will cost what, 10 or 15 cents total? In quantity you can get dual opamps for 25 cents or less. You can't get much cheaper than that. Fr. Tom McGahee ----- Original Message ----- From: "Russell McMahon" To: Sent: Friday, July 09, 2004 7:17 PM Subject: Re: [EE:] Design Challenge - Lowest cost PWM > Repost - says I've sent it already but I don't believe I have. > > > I realise that I have not made one thing clear enough - it's in the heading > but not (strangely) spelt out as clearly as could be in the text. The object > is LOWEST COST and also a complete "analog (or equivalent input) to PWM > output" circuit. There have been many interesting ideas, but quite a few > have no prospect of being lowest cost and some address only part of the > requirement. I find ALL circuit suggestions interesting so none of this is > wasted on me, but the unspecified (as yet unthought of) virtual (aka > non-existent :-) ) prize is for a complete lowest cost solution. > > > > Russell McMahon > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu