>
> Along another tack, you can get precise pulsetrains [but not single
> pulses] by using the PWM output on a PIC. You can get rep-rates
> from 1.2 khz to 5 mhz, and pulses as short as 50 nsec, when using a
> 20 mhz xtal. I have an appnote describing this:
>
> AN-ECD06 - Precision 50-nsec Pulse Generation Using a PIC16C63
>
> http://www.oricomtech.com/appnotes.htm
>
> There are 3 ranges, taking into account the 1x, 4x, and 16x
> prescaler values on Timer2. You can get 256 continuous rep-rates
> and 1024 pulsewidths from min to max in each of these ranges.
>
> Not as good as Tom's ckt, but costs you nothing if you are already
> using a PIC 16C6x/7x.
>
> - dan michaels
> ==============

> At 04:45 PM 3/16/01 +1100, you wrote:
> >Ok, but i'm using a 16F84 ;-)
> >
> >At a pinch i'll look at the 16C7x
> >
>
> Antonio,
>
> I just noticed the new 16C716 chip in the digikey catalog. It is
> 18-pin pinout like '84, and also has Timers 1/2 plus a PWM channel,
> which I presume works the same as all the other 2nd gen chips. You
> also get 4 real A/D channels - worth their weight in gold compared
> to those RC kludges that people use on '84 chips.
>
> - dan
> ========
>
>
> >Dan Michaels wrote:
> >>
> >> Along another tack, you can get precise pulsetrains [but not
> single
> >> pulses] by using the PWM output on a PIC. You can get rep-rates
> >> from 1.2 khz to 5 mhz, and pulses as short as 50 nsec, when using
> a
> >> 20 mhz xtal. I have an appnote describing this:
> >>
>
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>

>
> I am looking at modifying Tom Napier's NCO code for a numerically
> controlled digital output, ie; 1MHz instruction speed, 1kHz to 100kHz
> fOUT.
>
> Before reinventing the wheel. Has anyone done this before. If so would
> you be willing to share.
>
> Nino.
> --
> ------------------------------------------------------
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> ------------------------------------------------------

> Harold M Hallikainen wrote:
> >
> >         Yep, the PIC16c716 is a nice chip. We've designed it into
> a phase
> > controlled voltage regulator. It measures the instantaneous
> voltage 200
> > times every half cycle, accumulating the square of the voltage,
> then
> > dividing by the actual count (which may vary some depending on PIC
> and
> > line frequency), then taking the square root to get the RMS
> voltage. The
> > compare register is then adjusted in the appropriate direction to
> trigger
> > the triac at the right time so the RMS voltage remains constant
> > (relatively).
> >         We've shipped our first 500 and are about to start a run
> of 1,000.
> >
> > Harold
>
>
> Nice system Harold! Are you using a transformer
> too or does it just correct for over-power
> conditions?
> -Roman
>
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>

>
>         This system uses a 250W 24V halogen lamp. We're using an autotransformer
> to deliver about 30VAC open circuit, then phase controlling that down to
> 24V (actually, the RMS voltage to the lamp can be varied by a control
> voltage that is generated by another PIC generating a PWM signal and
> handling user interface). The autotransformer also has an isolated
> secondary that powers the PICs (three of them in this product, the 16c716
> in the power supply, a 16f628 in the control panel, and a 16f627 as a
> remote display driver/pushbutton interface that communicates with the
> control panel over three wires: +5V, data, ground).
>         The isolated secondary has its center tap grounded. One pair of
> rectifiers drives a capacitor and a 7805 to provide the 5V supply.
> Another pair of rectifiers drives a current limit resistor into RB0 to
> generate an interrupt just prior to zero cross. This resets the timer
> that the compare register uses to figure out when to turn on the triac.
> The same diode pair driving RB0 also drives a voltage divider into an
> analog input. This is where the instantaneous voltages during the half
> cycle are measured. Note that these samples are the full half cycle, not
> just the part when the triac is on. But, since the PIC is turning on the
> triac, we know when it's on. So, we just add zero instead of the A/D
> reading when the triac is not on.
>         Ideally, we'd measure the actual output driving the lamp, but that'd
> require another isolation barrier to get the phase controlled AC back to
> the PIC. I figured that the isolated secondary voltage is pretty close to
> being proportional to the nonisolated secondary (the portion of the
> primary between the bottom and the 30V tap). There'd be two errors: First
> would be a lack of tracking as the load varies. The second would be lack
> of tracing as the line varies. Since we are always driving the same load,
> the first factor (which is probably the larger one) can be ignored. I
> suspect the second factor is pretty small (the secondary voltage is
> pretty proportional to the line voltage).
>         So, it worked out pretty well. I was able to avoid another coupling
> across the isolation barrier...
>
> Harold