The fact that the dimmer generates the current to be sunk totally threw me
for a loop. Until now, **every** dimmer system that I have seen or read
about (admittedly theatrical and architectural)  has looked for a voltage,
usually 0 - 10v
When I went out to take a look at the dimmer in question, I measured the
voltage and it looked like it was 0 to 24v. When my interface box (which
generates 0 - 24v) didn't work, I did more research and discovered that the
dimmer was actually generating the current which was being sunk by the
controller.   A friend told me about a Programmable Logic Controller that
could sink the 4 to 20 mA that I need, and I was wondering how it did this
so I could replicate it with my pic.

Thanks for your advice!

> -----Original Message-----
> From: Dr. Imre Bartfai [mailto:root@prof.pmmf.hu]
> Sent: Tuesday, October 27, 1998 2:24 AM
> To: Andrew Yalowitz
> Cc: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Interfacing PIC to industrial automation
>
>
> Hi,
> use either some (bigger) PIC having built-in PWM, or write it in software
> (Scott has an excellent solution). The PIC is capable to generate voltage
> from 0 to 5 V. If the dimmer has the voltage without load also 5V, you are
> lucky. The total series resistor should be 250 ohms in this case. Are you
> sure the dimmer GENERATES current to be sunk?
>
> Imre
>
>
> On Mon, 26 Oct 1998, Andrew Yalowitz wrote:
>
> > I'm trying to interface a PIC to an industrial lighting dimmer that is
> > expecting a variable current sink of 4 to 20 mA.
> > What I would like to do is be able to sink current (4 to 20 mA)
> proportional
> > to an 8 bit value. The device (a lighting dimmer) is fully on
> at 4 mA and
> > fully off at 20 mA. I have been able to handle the user
> interface portion
> > and the processing of the data, but I have no clue how to get a
> pic to sink
> > a variable amount of current.
> >
> > Any advice?
> >
> > TIA
> >
> >
> > Andrew Yalowitz
> >
> >
>
>