Post by thread:ac line + pullups ??

hi & thanks for you time , i appreciate it this is my problem. switch a&b set a value (00.01,10,11) selected code is checked with lookup table ( on startup only ) table value placed in var "strttmr" continue with code swA |-----/ -----| rb0 gnd | | |------------------|-----/ -----| rb1 16f84 swB | ac | |--------/\/\/\/\------------------| rb3 10m with 240v the circuit works when a single strttmr value & no pullups are used. (SWITCHS A & B ARE NOT USED AT ALL) i am using rb3 to sense the ac line i/p.& synchronise (i am testing with 16vac till i get the code to work correctly) when i use pullups the prog won't work , because the ac i/p (rb3) doesn't go down to read a zero , goes no lower than 1.8v but when i get to using the 240v line voltage the same problem would arise, can't read zero crossing due to pullups! ***************** with this modification using selectable switch values via lookup table & since i need pullups to read the two switches.( at powerup only ) is their a way to code other than to enable pullups to get the switch values & then disable rb3 pullup so rb3 can sense line & synchronise(able to read zero crossing) (beside using 2 pullup res. on rb0 & rb1 keeping pullups disabled ) heres the code (lookup table only included in sub routines) ; vars PORTA equ 0x05 ;CPU equates (program memory map) PORTB equ 0x06 ;CPU equates (program memory map) souter equ 0x0c ; sinner equ 0x0d ; inners equ 0x0e ; outers equ 0x0f ; innerf equ 0x10 ; outerf equ 0x11 ; chkcnt equ 0x12 ; strttmr equ 0x13 ; no of counts switch equ 0x14 ; STATUS equ 0x03 ;CPU equates (program memory map) w equ 0 ; destination designators f equ 1 ; destination designators ;********************************************************************** ; porta set-up org 0x000 ;address 000 program start start movlw 0xff ;ff hex moved to w register tris PORTA ;porta set as inputs ; ;********************************************************************** ; PORTB set-up movlw 0x0f ;00001111 hex moved to w register tris PORTB ;PORTB set o/p's 4,5,6,7,inputs 0,1,2,3 ; ;********************************************************************** clrf STATUS ; ============= prescaler setup ============== movlw b'01000111' ;scale 1:256 , pullups enabled OPTION ; ============= counter setup ============== ;code below is used for 2 switches ; init strttmr from input pins movf PORTB,w ;get values of RB0 & RB1 andlw 0x03 ; extract out bits 0,1 of PORTB (strttmr value) CALL table ; use look up table movwf strttmr ;move selected value from table to strttmr ;********************************************************************** ; ============== program start ============= movlw 0x00 ;move 00 hex to register w movwf PORTB ;move register w to PORTB (clear PORTB) ; ============= initialise timer setup ============== initmr movlw .215 ;40 * .000256 = 10 ms movwf TMR0 loop CALL chcycs ;check for zero crossing CALL sttimer CALL tog ; ============= check timer ============== movf TMR0,w ;move f reg to w btfsc STATUS,Z ;if !0 ,GOTO loop GOTO loop decfsz strttmr,f ;decrement strttmr by 1 GOTO initmr ;go around for next delay ;drop thru to stop stop GOTO stop ;======================================================================= ; delay sub-routine table addwf PCL,f retlw d'25' ; 00 : 250ms (switch position 1) retlw d'50' ; 01 : 500ms (switch position 2) retlw d'75' ; 10 : 750ms (switch position 3) retlw d'100' ; 11 : 1000ms (switch position 4) thanks heaps in advance glen

thanks for letting me know , mark ! i was wondering why some of the postings i read were distorted. opto's are quite $$$ . space is a factor , i was going to use 2 diodes +res ac---------|>-----| res 240v |------/\/\/\-----|rb3 (values for 240v) ac---------|>-----| 10m i've tested this out on 16vac (res lower value)while i get the code working righ t.had no probs.with sync. the prob was pullups (set pullups does all portb pins) when pullups are used to get switch values the pullup on rb3 is at 1.8v & can't detect zero crossing. once the sw val.is selected (which is on powerup) i just remove pullups ,everyth ing ok then. thankyou very much for your time & advice glen ps if i was after better accuracy ,yeh i'd look at opto ************************** Mark Jurras wrote: > Glen, > > When posting code and schematics use a fixed width font such as Courier. Every computer has a > fixed width font. You posting was some variable spaced font that was different spacing than any > variable spaced font that I and many others have. It was difficult to read. > > I would use an opto-isolator on AC signal to generate the sync pulses. That wa y all the PIC inputs > would be at VCC levels and you get around all the internal diode conduction pr oblems that others > with better knowledge of the PIC can tell you about when you feed with HV on t he inputs. > > HTH, > > - -Mark > _________________________________________________________ > Do You Yahoo!? > Get your free @yahoo.com address at http://mail.yahoo.com

Hey Glen, I've just picked up on this thread so forgive me if I've missed something. What you are doing here is dangerous! I gather someone recommended optoisolators for the safety factor but if you think they're too expensive use a small power transformer with a low secondary winding (say 6.3vac) and a bridge rectifier (no filter capacitor) and resistive divider or zener to get your zero crossing points - if the application is mains powered you could even use your existing supply/plugpack if you insert an isolating diode in there to isolate the filter cap. Or you could make your own transformer using some turns around a current carrying wire - the result in either case being good isolation from the mains. Try and stay away from the single big resistor method as only special types are rated at high voltages (you may fry yourself as well as your micro...). In any application your safety and future persons' safety (who may access the unit) is paramount - with mains there is usually no second chance. Do it right the first time - safety first, price next. >ac---------|>-----| res > 240v |------/\/\/\-----|rb3 (values for 240v) >ac---------|>-----| 10m > Please don't take this as a flame. Regards, Bill W J Sherwood Senior Electronics Technician WNI Science & Engineering 31 Bishop St, Jolimont Perth, West Australia 6014 tel +61 8 9387 7955 fax +61 8 9387 6686

On Wed, 22 Apr 1998 11:31:13 +0200, you wrote: >). >> >>In any application your safety and future persons' safety (who may access >>the unit) is paramount - with mains there is usually no second chance. Do >>it right the first time - safety first, price next. >> >>>ac---------|>-----| res >>> 240v |------/\/\/\-----|rb3 (values for 240v) >>>ac---------|>-----| 10m >>> >> > >1/4W resistors are usually rated at 100V-200V depending on type. >Consider putting five 2M2 resistors in series. This gives you >some form of redundacy. Doing the same with the diodes might help, >but is not that important. Use metal-glaze resistors which are rated for high voltage operation. Resistors don't fail low-resistance. This is recognised even by very stringent safety standards like those for intrinsically-safe equipment for use in explosive atmospheres. Watch those creepage/clearence distances, though.

Mike Harrison wrote: {Quote hidden}> > On Wed, 22 Apr 1998 11:31:13 +0200, you wrote: > > >). > >> > >>In any application your safety and future persons' safety (who may access > >>the unit) is paramount - with mains there is usually no second chance. Do > >>it right the first time - safety first, price next. > >> > >>>ac---------|>-----| res > >>> 240v |------/\/\/\-----|rb3 (values for 240v) > >>>ac---------|>-----| 10m > >>> > >> > > > >1/4W resistors are usually rated at 100V-200V depending on type. > >Consider putting five 2M2 resistors in series. This gives you > >some form of redundacy. Doing the same with the diodes might help, > >but is not that important. > Use metal-glaze resistors which are rated for high voltage operation. > Resistors don't fail low-resistance. This is recognised even by very > stringent safety standards like those for intrinsically-safe equipment > for use in explosive atmospheres. Watch those creepage/clearence > distances, though. To protect the PIC inputs, I'd also split the resistor up into three series resistors and add a 10V Zener, a 10pF, and a 100pF cap in parallel on the node closest to the PIC. No transient = no comeback. -- Friendly Regards /"\ \ / Tjaart van der Walt X ASCII RIBBON CAMPAIGN spam_OUTtjaartTakeThisOuTwasp.co.za / \ AGAINST HTML MAIL |--------------------------------------------------| | WASP International | |R&D Engineer : GSM peripheral services development| |--------------------------------------------------| | Mobile : .....tjaartKILLspam@spam@sms.wasp.co.za (160 text chars) | | http://www.wasp.co.za/~tjaart/index.html | |Voice: +27-(0)11-622-8686 Fax: +27-(0)11-622-8973| | WGS-84 : 26¡10.52'S 28¡06.19'E | |--------------------------------------------------|

hmmm, what happens if one of the diodes just short circuit? Why don't use protective resistors "before" the diodes instead after? By the way, we already produced a power meter up to 480 Volts, and the best safety option for the current (and voltage) drop resistor is using at least 3 resistors in series, they isolate better high voltages and increase the damage caused by burnout possibility. Wagner. ps: exercising my pester position in this list, I'd like to say that a 10 meters resistor is the biggest I ever saw, and that Mr. Volt would be revolted seen his name in lower case (240v). :) Glen wrote: {Quote hidden}> > thanks for letting me know , mark ! > i was wondering why some of the postings i read were distorted. > > opto's are quite $$$ . space is a factor , i was going to use 2 diodes +res > > ac---------|>-----| res > 240v |------/\/\/\-----|rb3 (values for 240v) > ac---------|>-----| 10m > > i've tested this out on 16vac (res lower value)while i get the code working ri ght.had no probs.with > sync. > the prob was pullups (set pullups does all portb pins) when pullups are used t o get switch values the > pullup on rb3 is at 1.8v & can't detect zero crossing. > once the sw val.is selected (which is on powerup) i just remove pullups ,every thing ok then. > thankyou very much for your time & advice > glen

oh, I am sorry, I tought the device would has no human operator..., but lets calculate, suppose the unit is wired to 240VAC via 10 MOhms resistors, add more 200 kOhms for human body low resistance, the possible current through the body would be just less than 24uA, the same current that crosses your body when you touch directly a 12V battery or AC wall wart, it will not kill you, but... :) ... use an isolation transformer... even that thousands of old electronic equipment were produced without any isolation, and they carry live AC Voltage, sometimes the ground conductor is not even connected... I bet you have some appliance at your home that you don't dare to touch its metalic frame through a wire, while standing bare foot outside... :) Wagner Lipnharski wrote: {Quote hidden}> > hmmm, what happens if one of the diodes just short circuit? > Why don't use protective resistors "before" the diodes instead after? > > By the way, we already produced a power meter up to 480 Volts, and the > best safety option for the current (and voltage) drop resistor is using > at least 3 resistors in series, they isolate better high voltages and > increase the damage caused by burnout possibility. > > Wagner.