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HowTo: Build a 16 Ch PicDimmed Renard with SSRs onboard!
( Dave Johnson)
Step 10 : How many channels can I use at once?
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| | Phil Short and I have taken this design to 38400 bps with no problems. Thus at 25mS resolution you can drive 64 channels through a single serial port.
The math:
Theoretically, at 19200 baud it is possible to get up to 192 channels using 100ms resolution, but in the real world, with 100ms resolution 128 channels use 85-90ms of the 100ms cycle time. Thus you are at a 85% duty cycle when running 128 channels. In the picture above, Vixen is driving the serial port (RS232) with 100ms resolution and 128 channels. The width of the squares is 100ms, you can see what I mean by the statements above. In order to go beyond 128 channels at 19200 baud, you have a couple of options. The fastest and easiest is to just use another serial port. For each additional serial port you add, you can use another 128 channels. Vixen can natively support up to 4 serial ports, and some computers already have two serial ports on the back. Another option is to reduce your resolution from 100ms to 120ms for example. That would give you room for (theoretically) 20% more channels.
Phil and I continue to investigate using the external oscillator to push the frequency higher than 38400 bps, but that is a little bit harder, and will take some time and energy. I think we can have something running 57.6Kbps by April perhaps, maybe faster.
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