Dimmer

[BMIelektonik]

What would be the solution for following problem. I want to controll 2 opto SCR connected to RB1 RB2. I want one to increase light at the same time as the other Decrease light. The zero detection works perfect and also the delay for the ignition puls for scr1 but what about no 2.How do I solve it with Picbasic pro

Thanks





DELAY_1 = 8500 : us

POS_FLNK:IF ZERODETECT = 0 Then POS_FLNK
NEG_FLNK:IF ZERODETECT = 1 Then NEG_FLNK
DELAY_1 = DELAY_1 - 1

IF DELAY_1 < 7000 Then DELAY_1 = 7000

PauseUs DELAY_1
High out_1
"High out_2"
PauseUs 100
"Low out_1"
Low out_2

GoTo POS_FLNK

[ardhuru]

Hi,

Since you want to basically complement the 2 outputs, the timing part is easy; assuming you are on 50 Hz, your circuit should see a zero crossing every 10 ms. Therefore, if the delay for one output is X, the other would be (10000-X) us.

Now, the difficult part is that at times X will be less than (10000-X), and more than (10000-X) the other times.

You'll need to therefore determine the sequence of servicing the 2 outputs.

E.g., IF X < (10000-X) THEN PAUSEUS X, SWITCH ON TRIAC1, PAUSEUS (10000-X), SWITCH ON TRIAC2.

IF X > (10000-X) THEN PAUSEUS (10000-X), SWITCH ON TRIAC1, PAUSEUS X, SWITCH ON TRIAC2.

Take care of the situation when X = (10000-X) !

Also allow for the time taken for the actual execution, or else you'll miss the subsequent zero crossing. This you could do by taling the half cycle width to be, say, 9000 us seconds instead of 10000.

Hope this helps!

Regards,

Anand Dhuru

[BMIelektonik]

What about the timing of the trigger pulse when they meet in the center "50%dutycyle". At one point the pic will be busy with 100us pulse for SCR1 and at the same time SCR2 should be triggerd. this might give some flicker. maybe the solution would be to make the dimfunction in lets say 10 or 20 steps and then take care of the overlap instead of a linear dimfuntion


Thanks

[ardhuru]

I've found that the trigger pulse can be as narrow as 5uS; therefore the flicker you refer to is imperceptible.

Also, you could put in a line that caters specifically to this situation; e.g., if X = (1000-X) then High Out1 - Pauseus 5 - Low OUt1 - High Out2 - Pauseus 5 - Low Out2.

BTW, I am using traics, not SCRs. Any particular reason you are using SCRs?

Regards,

Anand

[BMIelektonik]

I am using a opto triac Sharp S216S01 so its not a SCR. have to check what the shortest triggpulse can be

Thanks for you input

[sougata]

Hi there,

Which PIC are you using ayway and how are you detecting the zero cross.

It is also important if you are detecting every or alternate zero crosses.

If you are using an interrupt based routine then do the following

1. Play with Timer0 and reset it every zero cross. All turn off the outputs. Its best to do it in assembly.
2. Thus your timer functions as a digital ramp generator now use to loop to detect if the timer has reached the desired value. In this way you do not have to care about the glitches.
3. A 5us time might be not enough. It is best to keep the outputs latched till the next zero cross. This will also let you use low loads under the latching current of the SCR.

Regards

Sougata