Decoding Pulse Telephone

[keithdoxey]

Thats interesting. I see two pair of wires coming out of the dial. So one pair is sure the digit pulser, the other might be exactly that, the home position. Maybe they used that to mute the earpiece?

Sure I can make good use to it.

Ioannis

The dials in British phones had 5 contacts. 2 of them were the pulsing contacts which were normally closed and pulsed open for the dial pulses. The other three contacts were normally open and are referred to as the "Dial Off Normal" contacts. They placed a short across the earpiece to prevent acoustic shock and also a short across the carbon granule microphone to prevent the back EMF surges from welding the granules together.

http://www.britishtelephones.com/howdial.htm

Keith

[Art]

Yes only two wires are needed for the phone in Australia too. I'm assuming there's access here to only use the dial mechanism.
None of our phones have an even make/break ratio though. It's maybe because the relays at the other end will close
quicker than they will open.
Old exchange equipment was the reason I was tasked with calibrating the dials.

A prettier example for counting the digits using the same method here:

[Ioannis]

OK, this is what I came up for decoding rotary dialer. It reads and decodes the pulses and compares 3 digits from the EEPROM. If one has different needs just change the arrays accordingly.

clear

read 0,array[0],array[1],array[2]    'array holds the stored digits to compare.

INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts

'wsave   var byte $20 system    'depends on the PIC used

':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler     TMR1_INT,   _Timer1,     PBP,    yes
    endm
    INT_CREATE 
ENDASM

@ INT_ENABLE  TMR1_INT     ; enable Timer 1 interrupts

goto main

Timer1:
    time=time+1      'Interrupt every 0,131msec for a 4MHz PIC clock
    if time>7 then   'time resets every 0,8 sec approximately
        time=0
    endif
@ INT_RETURN

main:

digit[0]=0:digit[1]=0:digit[2]=0    'clear array every time it loops here

for i=0 to 2                      'three digit counter. Change this for more
get_digit:
    while !dial:pause 10:wend    'wait for dial rotation
get_next
    time=0
    while dial
        if time>1 then main    'every digit takes around 10 ms. If times gets 1 
    wend                            'then it sure timed out
    digit[i]=digit[i]+1         'increment digit value
    time=0                        'reset time variable
    while !dial                   'wait for next high edge
        if time>4 then next_digit    'if time is more than 500-600ms then
    wend                          'next digit has arrived
    goto get_next
next_digit:
    if digit[i]<>array[i] then error    'if digit and array are different then wrong number dialed
    next i    

    high green:pause 1000:low green:goto main      'SUCCESS!  

error:
    high red:pause 1000:low red:goto main            'WRONG DIGITS!!!

end

Ioannis