Light dimmer problem

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- 5th July 2012, 14:49
FromTheCockpit

Light dimmer problem
I need some help in finding out how to connect zero-detector circuit to my PIC.
I do not wish to use any transformer in this circuit.

The circuit gets it's 12V from an external source which is reduced to 5V using 7805 in my circuit. I tried connecting 4 x 4.7Meg directly from mains to my PIC just to check if it works and it does, but not perfectly as I need to supply full-wave rectified voltage.

The problem:
- I am not sure of where to connect the ground connection of the bridge rectifier.
- Once the ground is connected to where it should, should I use the same resistance from the +ve side of the bridge to the PIC?
- 5th July 2012, 15:15
dhouston

Re: Light dimmer problem

Look for Microchip AN236 X-10® Home Automation Using the PIC16F877A. It includes schematics which should cover everything you need to know.
- 5th July 2012, 16:01
FromTheCockpit

Re: Light dimmer problem

Thanks. I checked your referred document. It doesn't seem to solve my problem. It does not provide full-wave rectification.
- 5th July 2012, 20:12
dhouston

Re: Light dimmer problem

Full-wave rectification of what? You said you were using an external power supply.

Numerous people have used the circuits in that appnote to control triac dimmers using the X10 powerline protocol.
- 5th July 2012, 20:23
FromTheCockpit

Re: Light dimmer problem

OK :smile:
I managed to tweak the code to fit in the direct resistance from the mains without the need for the bridge. The problem of flickering is still there, though not a lot but is still noticeable. Is something wrong with the code? I want to control 2 channels minimum with 1 IC, so I have set timer0 interrupt to happen @ 340uS approximately. This gives me approximately 29 steps for a 10mS interval. I just toggle the trigger edge at every Zero Crossing.

Code:

DEFINE OSC 20 ' OSCCON defaults to 20MHz on reset DEFINE NO_CLRWDT 1 Include "modedefs.bas" #CONFIG ifdef PM_USED device pic16F676, intrc_osc_noclkout, wdt_on, mclr_on, protect_off else __CONFIG _HS_OSC & _WDT_OFF & _MCLRE_OFF & _BODEN & _CP & _CPD endif #ENDCONFIG '----------Other pins Declared Here-------------- Dimmer1 VAR PortA.0 ' dimmer channel 1 Dimmer2 VAR PortC.0 ' dimmer channel 2 '----------Variables declared here---------------- Dimmer var Byte[2] ' timer value for 4 dimmer channels Count var Byte ' Dimmer working variable define INTHAND _ISR Goto main ISR: asm ' Context saving happens here btfsc INTCON, INTF goto ZeroCrossingInt T0Over bcf INTCON, T0IF ; clear the timer overflow flag movlw 203 movwf TMR0 incf _Count ; Increment Count ; check if channel1 value is reached movf _Dimmer+0,w subwf _Count,w btfsc STATUS,C bsf _Dimmer1 ; check if channel2 value is reached movf _Dimmer+1,w subwf _DimrWork,w btfsc STATUS,C bsf _Dimmer2 goto EndInt Set_Bit bsf OPTION_REG,6 clrf STATUS Goto EndInt ZeroCrossingInt bcf INTCON, INTF ; clear the interrupt clrf _Count ; Dimmer Working variable movlw 0 bcf STATUS,Z addwf _Dimmer+0,w btfss STATUS,Z bcf _Dimmer1 movlw 0 bcf STATUS,Z addwf _Dimmer+1,w btfss STATUS,Z bcf _Dimmer2 bsf STATUS,RP0 btfss OPTION_REG,6 Goto Set_Bit bcf OPTION_REG,6 clrf STATUS EndInt ; Context Restore here retfie endasm main: '----------Processor Initialisation--------------- PAUSE 50 TRISA = %001100 TRISC = 0 CMCON = 7 ANSEL = 0 OPTION_REG = %10000100 PORTA=%001100 PORTC=0 INTCON= %10110000 ' Global interrupts enabled ' Timer0 interrupt enabled ' Zero Crossing interrupt enabled ' Flags are cleared DIMMER[0]=0 : DIMMER[1]=25 Pause 3000 Start: DIMMER[0]=DIMMER[0]+1 DIMMER[1]=DIMMER[1]-1 Pause 3000 If Dimmer[0]=25 then Dimmer[0]=0 : Pause 3000 : Endif If Dimmer[1]=0 then Dimmer[1]=25 : Pause 3000 : Endif Goto start END

I am using 16f676 and 4 x 4.7Meg from Mains - Direct to PortA.2.
- 6th July 2012, 16:59
FromTheCockpit

Re: Light dimmer problem

Quote:

Originally Posted by dhouston

Full-wave rectification of what? You said you were using an external power supply.

Numerous people have used the circuits in that appnote to control triac dimmers using the X10 powerline protocol.

Full wave rectification of mains, I needed it for Zero-Crossing of mains. External power supply only provides 12V to my circuit. I checked the X-10 circuit but it has it's own transformer-less power supply and from there direct resistance is coming for Zero-crossing without any sort of rectification. I don't know much about X-10 so I am sorry if there is something I missed which you were trying to point out.

Anyways, since I have modified the code now the problem is of flickering of the bulb. Any comments about could be wrong?
:rolleyes::rolleyes:
- 6th July 2012, 19:00
dhouston

Re: Light dimmer problem

Quote:

Originally Posted by FromTheCockpit

Full wave rectification of mains, I needed it for Zero-Crossing of mains.

You do not need full wave rectification for zero-crossing detection. The circuit shown on p3, FIG3 of AN236 works fine for zero crossing. The appnote even details the inaccuracies inherent in the circuit, saying...

Quote:

On a rising edge, RB0 will go high about 64 µS after the zero-crossing, and on a falling edge, it will go low about 16 µS before the zero-crossing.

You'll find similar inaccuracies in most methods for zero-crossing detection. Their calculations are for 120VAC/60Hz. You'll need to adjust for 220V/50Hz (and maybe use a larger current limiting resistor).

One possible cause of flicker is failing to compensate for inaccurate zero crossing detection.

You can ignore the X10 communications circuitry and code but I suggest you study the code used for the triac dimmer circuit in AN236 (p6) or in the referenced PICREF-4 Reference Design, “PICDIM Lamp Dimmer for the PIC12C508”. The Microchip engineers frequently know what they are doing. ;)
- 7th July 2012, 07:17
ardhuru

Re: Light dimmer problem

Instead of feeding the mains to the pic pin, drive an opto like the PC814.

This has 2 LEDs in anti-parallel at the input, so you'd get 2 pulses for each mains cycle, one each for positive and negative. This will also give you a bonus of isolating your circuit from the mains.

Regards,

Anand Dhuru
- 7th July 2012, 14:55
FromTheCockpit

Re: Definitely problem with the circuit (or at least this is what it seems for now)

I played around with the circuit a little and it seems that the problem is with the circuit only.
My reason for saying this is because as soon as I connected the ground of my oscilloscope with the 12V ground which comes from an external source (smps), the flickering suddenly stopped and glowing of the bulb at different brightness levels was just as expected, smooth and perfect. As soon as I removed the ground of my oscilloscope the flickering started again.
- 7th July 2012, 15:25
FromTheCockpit

Re: Light dimmer problem

Quote:

Originally Posted by ardhuru

Instead of feeding the mains to the pic pin, drive an opto like the PC814.

This has 2 LEDs in anti-parallel at the input, so you'd get 2 pulses for each mains cycle, one each for positive and negative. This will also give you a bonus of isolating your circuit from the mains.

Regards,

Anand Dhuru

Thanks for the reply. What resistance values normally goes for the opto side of the PC814 and what should be the wattage of this resistance values. I am @ 240VAC
- 9th July 2012, 10:12
ardhuru

Re: Light dimmer problem

I'd used 100K, 1W on 240 VAC.

Reducing the resistance would get you sharper edges, but then one needs a resistance of a higher wattage, so I finally settled on these, and its worked great for me.
- 9th July 2012, 10:49
Megahertz

Re: Light dimmer problem

I wonder if 4n25 can be used the same way?
(with 100k direct to Live and other end to neutral)
- 9th July 2012, 12:36
ardhuru

Re: Light dimmer problem

Looks like the 4n25 has only 1 diode at the input. You'd get only 1 pulse per cycle. If thats acceptable, I dont see why the 4n25 shouldnt work.

Regards,

Anand