Which chip do i use?

[The Master]

Darrel. I changed the design yesterday. I only need 16 PWM pins now. Someone made some circuits for me years ago that do exactly what im trying to do now and they work perfect. They only used smaller chips i think PIC16F84's. The person who made them lost the origional code in a format and i hardly ever see him online now. I guess he wasnt using your code though. Ive swapped to a PIC16F877A now. I hope that will do better.

Im not sure about the frequency/resolution. I want a brightness control that is 0-100%. Here in the UK we have 50Hz which means 100 zero-crossings per second so i think for 100 brightness levels i should split each half cycle into 100. That should mean for a brightness level of 50% i wait 5ms before turning the output on. Im not sure how this would work though because 1% would be 100ns but isnt that faster than the chip can handle?
Im sure im going about this bit the wrong way too.

I checked the datasheet for PIC16F877A and it says it has USART So that should be ok.

mackrackit. Its all becoming clear now. Im about to read through that thread now but i think i understand how it should work.

Random thought. I can upload the .HEX file from one of the chips i have already doing this kind of thing with 8 PWM outputs. I dont know if anyone can do anything with it. Maby decompile to assembly?

[The Master]

Just read through that thread and the PDF in it. I only understood some of it through. Im using triacs so i cant use bi-phase angle modulation. Phase angle modulation is what i was thinking of. Turn an output on at a set point durin the half cycle and let the triac turn itself off at the next zero-crossing. I dont think the drawbacks of that method will affect me because im not using LEDs. I got completely lost at BAM.

The idea i had would work like this

interruptpoint: 'This is where it goes on interrupt from the zero-crossing pin RB0
if brightness(0)=100 then
high porta.0
endif
if brightness(1)=100 then
high porta.1
endif
.........
pause (100th of a cycle)
if brightness(0)=99 then
high porta.0
endif
......
'by now it should be right at the end of the half cycle
'set the pins to low so the triacs dont all come back on in the next half cycle
low porta.0
low porta.1
resume

Obviously i wouldnt type out hundreds of if statements, i would use a loop instead but thats what i was thinking of. It looks a little slow though

I know ive got to learn serial now without using serin2.
Which interrupt method do i need? (or which one should i start learning?)

[Darrel Taylor]

Should I also guess that the serial is comming in at 250kbaud?
There are 512 frames, at ~40hz.
A.K.A. ... DMX

.

[The Master]

I was going to use 9600n. Thats what everything else uses including the origional boxes my mate made

EDIT: The plan wasnt to use these as DMX lights but how hard would that be? IVe got a DMX controller and i think its faster than anything ive done using the serial port (My DMX box is USB>DMX)

[The Master]

Hehe. Ive had a quick google of DMX in PBP and it sent me to this thread. BTW, the person who made my origional boxes is electronicsuk (Matt).

After reading that thread im not sure about DMX. I looked at assembler once then quickly made a break for the exit

[Darrel Taylor]

... The plan wasnt to use these as DMX lights but how hard would that be?

Very!

Got paid to do it once.
Came up with 1 18F as the front end receiving the DMX.
And any number of slaves (8 per PIC).
Up to 512 channels total. (lots of slaves, kinky)

Unfortunately, it was for LED's (high powered one's, but still LED's)
It'll be harder for A/C dimmers.

.

[The Master]

DMX is out then! I dont want this to be any harder than it already is.

Ive just been reading some of Matt's threads. I can see a few references to the boxes he made for me. Just to add, those boxes are still working perfect after something like 3 or 4 years. Nice job!

Anyways. I cant seem to find much in those threads about the bits im stuck on. There is 1 thing that can be learned from them tho. Dont rivet triacs to anything! I had to replace one once without getting to the solder side of the PCB.

This thread or more specificly the last post is quite interesting. Can someone tell me if the following is correct.
There is a receive flag. Possibly whatever PBP uses as a boolean value. When serial data arrives at the chip this flag is set to true.

RCREG returns the first byte from the serial buffer and removes it from the buffer. If this causes the buffer to be empty (that was the last byte) then the RX flag is set to false.

I take it this uses the hardware UART thing to add data to a buffer (with no code)

[The Master]

Ive just found another thread with sample code of using UART and interrupts. It looks simple enough so im gonna test it out when i get back home (stupid work, ruining my day :P)