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continuity tester

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FPGA for a continuity tester? Use bi-directional shift registers.
 
i using a PIC16F628 with PORTA configure just like Nigel's LCD board and PORTB with bit7 a the input and the rest as output, firstly i use bit 6 of PORTB as the input to the enable of the first stage decoders (consist of two 3to8 decoders) (with the second one control by 0 via a not gate) then bit 5,4,3 as the input to the first stage decoder select lines (which is tie together pin to pin) followed by bit 2,1,0 to the select lines of the second stage decoders (which consist of 16 decoders also tie together), the first stage decoders is use to control the enable pins of the second stage decoders and lastly the output of the second stage decoders are all tie together to bit 7 of PORTB

*this idea is contributed by amitak

now that i had configure the PIC this way, i written a program based on using the LCD Subroutines by Nigel, while i wait for the components to arrive for me to test, i tt that i upload the program i wrote and maybe can get some advices from you all because this is the first time i writing a PIC program
Code: 
	LIST	p=16F628		;tell assembler what chip we are using
	include "P16F628.inc"		;include the defaults for the chip
	ERRORLEVEL	0,	-302	;suppress bank selection messages
	__config 0x3D18			;sets the configuration settings (oscillator type etc.)




		cblock	0x20			;start of general purpose registers
			count			;used in looping routines
			count1			;used in delay routine
			counta			;used in delay routine
			countb			;used in delay routine
			tmp1			;temporary storage
			tmp2
			templcd			;temp store for 4 bit mode
			templcd2
			Acc
	
		endc

LCD_PORT	Equ	PORTA
LCD_TRIS	Equ	TRISA
LCD_RS		Equ	0x04			;LCD handshake lines
LCD_RW		Equ	0x06
LCD_E		Equ	0x07

		org	0x0000
		goto	Start

Main_Text	addwf	PCL, f
		retlw	'S'
		retlw	'T'
		retlw	'A'
		retlw	'R'
		retlw	'T'
		retlw	'I'
		retlw	'N'
		retlw	'G'
		retlw	0x00

Text_wire		addwf	PCL, f
		retlw	'W'
		retlw	'i'
		retlw	'r'
		retlw	'e'
		retlw	' '
		retlw	0x00

Text_pass	addwf PCL, f
		retlw	'P'
		retlw	'A'
		retlw	'S'
		retlw	'S'
		retlw	0x00

Text_fail	addwf PCL, f
		retlw	'F'
		retlw	'A'
		retlw	'I'
		retlw	'L'
		retlw	0x00

Start		movlw	0x07
		movwf	CMCON			;turn comparators off (make it like a 16F84)

Initialise	clrf	count
		clrf	PORTA
		clrf	PORTB
		clrf	Acc
;		clrf	NumL
;		clrf	NumH



SetPorts	bsf 	STATUS,		RP0	;select bank 1
		movlw	b'00010000'			;PORT A for LCD
		movwf	LCD_TRIS
		movlw	b'10000000'			;PORT B for Decoder
		movwf	TRISB
		bcf 	STATUS,		RP0	;select bank 0

		call	LCD_Init		;setup LCD
		Call	Delay255

		clrf	count			;set counter register to zero
Main	movf	count, w		;put counter value in W
		call	Main_Text			;get a character from the text table
		xorlw	0x00			;is it a zero?
		btfsc	STATUS, Z
		goto	Sub_Main
		call	LCD_Char
		incf	count, f
		goto	Main

Sub_Main	Call	Delay255
			btfss	PORTA, 4
			Goto	Sub_Main
			Call 	Delay255	
			movlw	b'01001000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01010000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01011000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01100000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01101000'
			movwf	PORTB
			Call 	Delay255
			Call	Repeat
			movlw	b'01110000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01111000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00001000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00010000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00011000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00100000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00101000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00110000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00111000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			Goto	Start

Repeat		bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bsf		PORTB, 1
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bcf		PORTB, 1
			bsf		PORTB, 2
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bsf		PORTB, 1
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			Return

Check		Call	LCD_Clr
			Call	Delay255
			clrf	count			;set counter register to zero
Check_Sub		movf	count, w		;put counter value in W
			call	Text_wire			;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Check_main
			call	LCD_Char
			incf	count, f
			goto	Check_Sub
			
Check_main		Call	Delay255
			movlw	5
			Call	LCD_Line1W
			Incf	Acc, w
			btfsc	Acc, 7
			Goto	Start
			btfsc	PORTB, 7
			Goto	Pass
			Goto	Fail
Ret			Return

Pass		Call 	Delay255
			Call	LCD_CharD
			Call	LCD_Line2
			clrf	count			;set counter register to zero
Pass_Sub	movf	count, w
			Call	Text_pass		;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Ret
			call	LCD_Char
			incf	count, f
			goto	Pass_Sub

Fail		Call 	Delay255
			Call	LCD_CharD
			Call	LCD_Line2
			clrf	count			;set counter register to zero
Fail_Sub	movf	count, w
			Call	Text_fail		;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Ret
			call	LCD_Char
			incf	count, f
			goto	Fail_Sub	

;Subroutines and text tables

;LCD routines

;Initialise LCD
LCD_Init call 	LCD_Busy		;wait for LCD to settle

		movlw	0x20			;Set 4 bit mode
		call	LCD_Cmd

		movlw	0x28			;Set display shift
		call	LCD_Cmd

		movlw	0x06			;Set display character mode
		call	LCD_Cmd

		movlw	0x0c			;Set display on/off and cursor command
		call	LCD_Cmd			;Set cursor off

		call	LCD_Clr			;clear display

		retlw	0x00

; command set routine
LCD_Cmd		movwf	templcd
		swapf	templcd,	w	;send upper nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bcf	LCD_PORT, LCD_RS	;RS line to 0
		call	Pulse_e			;Pulse the E line high

		movf	templcd,	w	;send lower nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bcf	LCD_PORT, LCD_RS	;RS line to 0
		call	Pulse_e			;Pulse the E line high
		call 	LCD_Busy
		retlw	0x00

LCD_CharD	addlw	0x30			;add 0x30 to convert to ASCII
LCD_Char	movwf	templcd
		swapf	templcd,	w	;send upper nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bsf	LCD_PORT, LCD_RS	;RS line to 1
		call	Pulse_e			;Pulse the E line high

		movf	templcd,	w	;send lower nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bsf	LCD_PORT, LCD_RS	;RS line to 1
		call	Pulse_e			;Pulse the E line high
		call 	LCD_Busy
		retlw	0x00

LCD_Line1	movlw	0x80			;move to 1st row, first column
		call	LCD_Cmd
		retlw	0x00

LCD_Line2	movlw	0xc0			;move to 2nd row, first column
		call	LCD_Cmd
		retlw	0x00

LCD_Line1W	addlw	0x80			;move to 1st row, column W
		call	LCD_Cmd
		retlw	0x00

LCD_Line2W	addlw	0xc0			;move to 2nd row, column W
		call	LCD_Cmd
		retlw	0x00

LCD_CurOn	movlw	0x0d			;Set display on/off and cursor command
		call	LCD_Cmd
		retlw	0x00

LCD_CurOff	movlw	0x0c			;Set display on/off and cursor command
		call	LCD_Cmd
		retlw	0x00

LCD_Clr		movlw	0x01			;Clear display
		call	LCD_Cmd
		retlw	0x00

Delay255	movlw	0xff			;delay 255 mS
		goto	d0
Delay100	movlw	d'100'			;delay 100mS
		goto	d0
Delay50		movlw	d'50'			;delay 50mS
		goto	d0
Delay20		movlw	d'20'			;delay 20mS
		goto	d0
Delay5		movlw	0x05			;delay 5.000 ms (4 MHz clock)
d0		movwf	count1
d1		movlw	0xC7			;delay 1mS
		movwf	counta
		movlw	0x01
		movwf	countb
Delay_0
		decfsz	counta, f
		goto	$+2
		decfsz	countb, f
		goto	Delay_0

		decfsz	count1	,f
		goto	d1
		retlw	0x00

Pulse_e		bsf	LCD_PORT, LCD_E
		nop
		bcf	LCD_PORT, LCD_E
		retlw	0x00

LCD_Busy
		bsf	STATUS,	RP0		;set bank 1
		movlw	0x0f			;set Port for input
		movwf	LCD_TRIS
		bcf	STATUS,	RP0		;set bank 0
		bcf	LCD_PORT, LCD_RS	;set LCD for command mode
		bsf	LCD_PORT, LCD_RW	;setup to read busy flag
		bsf	LCD_PORT, LCD_E
		swapf	LCD_PORT, w		;read upper nibble (busy flag)
		bcf	LCD_PORT, LCD_E		
		movwf	templcd2 
		bsf	LCD_PORT, LCD_E		;dummy read of lower nibble
		bcf	LCD_PORT, LCD_E
		btfsc	templcd2, 7		;check busy flag, high = busy
		goto	LCD_Busy		;if busy check again
		bcf	LCD_PORT, LCD_RW
		bsf	STATUS,	RP0		;set bank 1
		movlw	0x00			;set Port for output
		movwf	LCD_TRIS
		bcf	STATUS,	RP0		;set bank 0
		return

;end of LCD routines

		end
 
nitE,
Do you have a circuit you could post.?

Using only LS138, IMO will not give the result you are expecting.:)
 
i think i better try to explain what am i writing

i try to set each output of the second stage decoder on one by one and after which check bit 7 of PORTB and if on, display PASS and if off, display FAIL

the setting of the outputs is done first by only setting the first 5 bits of PORTB(6,5,4,3 and 7 is output) and after that call repeat which is the last 3 bits which consist of the pattern(001,010,011,100,101,110,111) and then call check which is use to check bit 7 after that is the pass or fail

i display 'Wire' in the first line and after that by the number which is store in Acc (it increment everytime the program come into Check) and the value is store in the working register and display using Call LCD_CharD, the pass/fail is display on the second line..

hope i dont confuse you more..:eek:
 
nitE said:
i think i better try to explain what am i writing

i try to set each output of the second stage decoder on one by one and after which check bit 7 of PORTB and if on, display PASS and if off, display FAIL

the setting of the outputs is done first by only setting the first 5 bits of PORTB(6,5,4,3 and 7 is output) and after that call repeat which is the last 3 bits which consist of the pattern(001,010,011,100,101,110,111) and then call check which is use to check bit 7 after that is the pass or fail

i display 'Wire' in the first line and after that by the number which is store in Acc (it increment everytime the program come into Check) and the value is store in the working register and display using Call LCD_CharD, the pass/fail is display on the second line..

hope i dont confuse you more..:eek:
Click to expand...

I am not confused,;) just not convinced.

Post a sketch.:)
 
ericgibbs said:
In my opinion... I would like to see a circuit diagram before looking at a program.:)
Click to expand...

:D, ok i will draw one then
anyway, the above program is slighty wrong
this is the 'correct' one (myself think one)

Code: 
	LIST	p=16F628		;tell assembler what chip we are using
	include "P16F628.inc"		;include the defaults for the chip
	ERRORLEVEL	0,	-302	;suppress bank selection messages
	__config 0x3D18			;sets the configuration settings (oscillator type etc.)




		cblock	0x20			;start of general purpose registers
			count			;used in looping routines
			count1			;used in delay routine
			counta			;used in delay routine
			countb			;used in delay routine
			tmp1			;temporary storage
			tmp2
			templcd			;temp store for 4 bit mode
			templcd2
			Acc
	
		endc

LCD_PORT	Equ	PORTA
LCD_TRIS	Equ	TRISA
LCD_RS		Equ	0x04			;LCD handshake lines
LCD_RW		Equ	0x06
LCD_E		Equ	0x07

		org	0x0000
		goto	Start

Main_Text	addwf	PCL, f
		retlw	'S'
		retlw	'T'
		retlw	'A'
		retlw	'R'
		retlw	'T'
		retlw	'I'
		retlw	'N'
		retlw	'G'
		retlw	0x00

Text_wire		addwf	PCL, f
		retlw	'W'
		retlw	'i'
		retlw	'r'
		retlw	'e'
		retlw	' '
		retlw	0x00

Text_pass	addwf PCL, f
		retlw	'P'
		retlw	'A'
		retlw	'S'
		retlw	'S'
		retlw	0x00

Text_fail	addwf PCL, f
		retlw	'F'
		retlw	'A'
		retlw	'I'
		retlw	'L'
		retlw	0x00

Start		movlw	0x07
		movwf	CMCON			;turn comparators off (make it like a 16F84)

Initialise	clrf	count
		clrf	PORTA
		clrf	PORTB
		clrf	Acc
;		clrf	NumL
;		clrf	NumH



SetPorts	bsf 	STATUS,		RP0	;select bank 1
		movlw	b'00010000'			;PORT A for LCD
		movwf	LCD_TRIS
		movlw	b'10000000'			;PORT B for Decoder
		movwf	TRISB
		bcf 	STATUS,		RP0	;select bank 0

		call	LCD_Init		;setup LCD
		Call	Delay255

		clrf	count			;set counter register to zero
Main	movf	count, w		;put counter value in W
		call	Main_Text			;get a character from the text table
		xorlw	0x00			;is it a zero?
		btfsc	STATUS, Z
		goto	Sub_Main
		call	LCD_Char
		incf	count, f
		goto	Main

Sub_Main	Call	Delay255
			btfss	PORTA, 4
			Goto	Sub_Main
			Call 	Delay255
			movlw	b'01000000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255	
			movlw	b'01001000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01010000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01011000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01100000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01101000'
			movwf	PORTB
			Call 	Delay255
			Call	Repeat
			movlw	b'01110000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'01111000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00000000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00001000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00010000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00011000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00100000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00101000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00110000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			movlw	b'00111000'
			movwf	PORTB
			Call	Repeat
			Call 	Delay255
			Goto	Start

Repeat		Call	Check
			Call	Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bsf		PORTB, 1
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bcf		PORTB, 1
			bsf		PORTB, 2
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			bcf		PORTB, 0
			bsf		PORTB, 1
			Call	Check
			Call    Delay255
			bsf		PORTB, 0
			Call	Check
			Call    Delay255
			Return

Check		Call	LCD_Clr
			Call	Delay255
			clrf	count			;set counter register to zero
Check_Sub		movf	count, w		;put counter value in W
			call	Text_wire			;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Check_main
			call	LCD_Char
			incf	count, f
			goto	Check_Sub
			
Check_main		Call	Delay255
			movlw	5
			Call	LCD_Line1W
			Incf	Acc, w
			btfsc	Acc, 7
			Goto	Start
			btfsc	PORTB, 7
			Goto	Pass
			Goto	Fail
Ret			Return

Pass		Call 	Delay255
			Call	LCD_CharD
			Call	LCD_Line2
			clrf	count			;set counter register to zero
Pass_Sub	movf	count, w
			Call	Text_pass		;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Ret
			call	LCD_Char
			incf	count, f
			goto	Pass_Sub

Fail		Call 	Delay255
			Call	LCD_CharD
			Call	LCD_Line2
			clrf	count			;set counter register to zero
Fail_Sub	movf	count, w
			Call	Text_fail		;get a character from the text table
			xorlw	0x00			;is it a zero?
			btfsc	STATUS, Z
			goto	Ret
			call	LCD_Char
			incf	count, f
			goto	Fail_Sub	

;Subroutines and text tables

;LCD routines

;Initialise LCD
LCD_Init call 	LCD_Busy		;wait for LCD to settle

		movlw	0x20			;Set 4 bit mode
		call	LCD_Cmd

		movlw	0x28			;Set display shift
		call	LCD_Cmd

		movlw	0x06			;Set display character mode
		call	LCD_Cmd

		movlw	0x0c			;Set display on/off and cursor command
		call	LCD_Cmd			;Set cursor off

		call	LCD_Clr			;clear display

		retlw	0x00

; command set routine
LCD_Cmd		movwf	templcd
		swapf	templcd,	w	;send upper nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bcf	LCD_PORT, LCD_RS	;RS line to 0
		call	Pulse_e			;Pulse the E line high

		movf	templcd,	w	;send lower nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bcf	LCD_PORT, LCD_RS	;RS line to 0
		call	Pulse_e			;Pulse the E line high
		call 	LCD_Busy
		retlw	0x00

LCD_CharD	addlw	0x30			;add 0x30 to convert to ASCII
LCD_Char	movwf	templcd
		swapf	templcd,	w	;send upper nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bsf	LCD_PORT, LCD_RS	;RS line to 1
		call	Pulse_e			;Pulse the E line high

		movf	templcd,	w	;send lower nibble
		andlw	0x0f			;clear upper 4 bits of W
		movwf	LCD_PORT
		bsf	LCD_PORT, LCD_RS	;RS line to 1
		call	Pulse_e			;Pulse the E line high
		call 	LCD_Busy
		retlw	0x00

LCD_Line1	movlw	0x80			;move to 1st row, first column
		call	LCD_Cmd
		retlw	0x00

LCD_Line2	movlw	0xc0			;move to 2nd row, first column
		call	LCD_Cmd
		retlw	0x00

LCD_Line1W	addlw	0x80			;move to 1st row, column W
		call	LCD_Cmd
		retlw	0x00

LCD_Line2W	addlw	0xc0			;move to 2nd row, column W
		call	LCD_Cmd
		retlw	0x00

LCD_CurOn	movlw	0x0d			;Set display on/off and cursor command
		call	LCD_Cmd
		retlw	0x00

LCD_CurOff	movlw	0x0c			;Set display on/off and cursor command
		call	LCD_Cmd
		retlw	0x00

LCD_Clr		movlw	0x01			;Clear display
		call	LCD_Cmd
		retlw	0x00

Delay255	movlw	0xff			;delay 255 mS
		goto	d0
Delay100	movlw	d'100'			;delay 100mS
		goto	d0
Delay50		movlw	d'50'			;delay 50mS
		goto	d0
Delay20		movlw	d'20'			;delay 20mS
		goto	d0
Delay5		movlw	0x05			;delay 5.000 ms (4 MHz clock)
d0		movwf	count1
d1		movlw	0xC7			;delay 1mS
		movwf	counta
		movlw	0x01
		movwf	countb
Delay_0
		decfsz	counta, f
		goto	$+2
		decfsz	countb, f
		goto	Delay_0

		decfsz	count1	,f
		goto	d1
		retlw	0x00

Pulse_e		bsf	LCD_PORT, LCD_E
		nop
		bcf	LCD_PORT, LCD_E
		retlw	0x00

LCD_Busy
		bsf	STATUS,	RP0		;set bank 1
		movlw	0x0f			;set Port for input
		movwf	LCD_TRIS
		bcf	STATUS,	RP0		;set bank 0
		bcf	LCD_PORT, LCD_RS	;set LCD for command mode
		bsf	LCD_PORT, LCD_RW	;setup to read busy flag
		bsf	LCD_PORT, LCD_E
		swapf	LCD_PORT, w		;read upper nibble (busy flag)
		bcf	LCD_PORT, LCD_E		
		movwf	templcd2 
		bsf	LCD_PORT, LCD_E		;dummy read of lower nibble
		bcf	LCD_PORT, LCD_E
		btfsc	templcd2, 7		;check busy flag, high = busy
		goto	LCD_Busy		;if busy check again
		bcf	LCD_PORT, LCD_RW
		bsf	STATUS,	RP0		;set bank 1
		movlw	0x00			;set Port for output
		movwf	LCD_TRIS
		bcf	STATUS,	RP0		;set bank 0
		return

;end of LCD routines

		end
 
well, here is my circuit..
 

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here is how PORTA is configure, the same way nigel did his..
the pic is taken from his website
 

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nitE said:
well, here is my circuit..
Click to expand...

hi nitE,
I guess you know the selected output of a LS138 is LOW.
As all the 100 wires are linked back to the other LS138 HIGH outputs, the active pin will not sink 99 high outputs, the LS138 is not tri-state.
 
I know my opinion has not been asked, but I will give it anyways. A 100 pin cable will be a disaster to build, and to be reliable will be an equal problem. The biggest cable I have ever seen built was a 96 pin digital video cable and it was a manufacturing nightmare. You would be better off to partition the 100 pin I/O into 3 separate cables. Perhaps your board design is already done, in which case I guess you are stuck.
 
yes as said by eric the active low out cannot sink the current of other outputs :(
maybe u can use a 1:8 multiplexer (and connect the input to Vcc) or look for another part number with trisate outputs
yes the lcd display routines take up most of the program ..
to me it seems that it would not be necessary to display the pass/fail for each wire ..
maybe scan through all the 100 wires and then just say if all are ok .. or the list of wires which are not (remember to leave some delay for the user to read the result
 
amitak said:
yes as said by eric the active low out cannot sink the current of other outputs :(
maybe u can use a 1:8 multiplexer (and connect the input to Vcc) or look for another part number with trisate outputs
yes the lcd display routines take up most of the program ..
to me it seems that it would not be necessary to display the pass/fail for each wire ..
maybe scan through all the 100 wires and then just say if all are ok .. or the list of wires which are not (remember to leave some delay for the user to read the result
Click to expand...

I use the HEF4067B analog mux/demux it this type of application.:)
 
100 pin cable still sounds like problems to me... I would not do it.
 
If one wire faults... what a nightmare.
 
Hi,

I had to read this carefully, in case i got it wrong.

do anyone here know how can i build a continuity tester which can test 100 wires at the same time and the result to be display on a lcd? thank you!

After i read this thread a couple of times, i concluded that i havent got it wrong.

The poster doesnt say its a cable, he says "100 wires".
This may well be in the form of a loom, maybe for a motor car, or similar.
Being able to pinpoint a faulty wire easily could save a lot of time.
And if its a loom prior to being wrapped, then a wire could be changed.
Such a unit might only have to save a few looms to pay for itself.

************

To check 100 wires simultaneously requires a lot of circuitry.
i will appeciate if i don't need to use a MCU, i don't mind if the circuit is big..

So whats the minimum set-up here ?
A hundred connections with a light on each. And a hundred connections at the other end, all taken to common.

An unlit light should stand out clearly.

Complicated ?
Not really, its about as simple as possible.
Being straightforward means it can be made easily.
More importantly, its easy to understand. Which makes it easy to repair if needed.

Indication.
The OP says he wants to use a liquid crystal display to show the results.
These are usually matrixed up, which just makes more problems.
I would suggest LEDs, and a dummy load on each wire, to load each wire to its required current rating. This is in order that any wire or its associated connection would show up if it cannot handle the current required.

Such a unit would be easy to make, and would show all the wires at once with 100 LEDs.

************

I dunno, the more i read this thread, the more it looks like another introduction to MCUs.

Best of luck with it, John :)
 
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