On Mon, 14 Jul 1997 16:28:54 -0400 Andy Kunz <montana@FAST.NET> writes:
>At 02:23 PM 7/14/97 EDT, you wrote:
>>bunch (maybe a dozen) of these in it with serial control (ideally with
a
>>serial out so the data can be looped into more PWM controllers).  I'd
>>like to be able to send a number into each of these PWM circuits and
get
>>a pulse whose width is proportional to the number.  Most PWM stuff I've
>>seen has been single channel and pretty much an analog circuit (PWM out
>>proportional to analog input).  Any digital PWM peripherals out there?
>
>Harold,
>
>My generic robotic controller does this, sort of.  It accepts commands
via
>RS-232 or 485 (or R/C PWM, depending upon software configuration).  It
>outputs R/C PWM to up to 16 channels, each channel gets a 2mS slot with
>data up to 2mS wide, on a rotating basis.  If you use a serial input,
the
>two PWMs through the 16 channels at the same time (one PWM module runs 8
>channels, the other runs the other 8) for a complete refresh to each
>channel every 16mS.  If you go with a R/C PWM input, the signal cycles
>every 32mS.
>

        I did something like this to decode DMX512 (a lighting control
protocol) out to analog.  Set up a single PWM channel in a 16c74a to
output 20 pulses of appropriate width (proportional to the analog out for
that channel) through a resistor through a 4051 demux to a capacitor to
ground.   The single series resistor and all the capacitors to ground on
the 4051 outputs formed a conbination low pass filter and sample/hold.
When the demux was on another channel, the capacitor holds the last
voltage it was at due to the LPF of the PWM.  This is followed by a
non-inverting amp to provide gain and a low output resistance.
        So...  did something like your controller already (it's been in
production for a few months now).
        The PWM controller I'm looking for would ideally give me 12 to 16
channels of continuous PWM at 20 to 50 KHz.  I want to do 12 to 16
channels of digitally controlled buck (as opposed to boost) voltage
control.  Any digital peripheral chips like that out there?


Thanks!

Harold