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telephone monitoring circuit

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KMoffett

Well-Known Member
ravi17,

That's my circuit. It was part of a system that did many, many years ago to add HOLD to all the phones in my home. To use it with a micro-controller just use +5VCD on the opto-transistors instead of +12VDC. Then you can use the two opto outputs to have the micro-controller logic determine the three states:
On-Hook: Upper LO and Lower HI
Ring: Both Upper and Lower Pulsing
Off-Hook: Upper HI and Lower HI

Ken

Telephone interface-1.gif
 

ravi17

New Member
hi,
the circuit is not so detailed. can you tell which diodes you are using in the bridge and also the zener diodes? is it 6Vz or 6Yz?
i will try this circuit
 

KMoffett

Well-Known Member
6v Zener 1N4735 or equivalent
56V Zener 1N4658 or equivalent
Bridge diodes 1N4002 or equivalent

Ken
 

ravi17

New Member
the condition is exactly opposite for on-hook and off-hook,
On-Hook: Upper HI and Lower HI
Off-Hook: Upper LO and Lower HI

could you confirm?

thanks
 

Colin

Active Member
That circuit will not allow the line to open. You cannot leach any more than 0.5mA for the line to open.
 

ravi17

New Member
more importantly, i do not understand the output interface to microcontroller. the output is connected to 5V supply via 100k. The voltage is in the output for on and off hook is 1.55V and 0.12V. how to interpret these are logic 1 and 0? then the ringing signal is ac signal. how to convert this to 1 or 0?
 

Colin

Active Member
Look, I think this simple project is way over your head.
You are asking questions you should know if you are using a micro.
Don't you know anything about "poling" an input????
 

ravi17

New Member
Look, I think this simple project is way over your head.
You are asking questions you should know if you are using a micro.
Don't you know anything about "poling" an input????
I have heard "poling" for the first time. http://www.dictionary.com/browse/poling:
verb: to propel a boat, raft, etc., with a pole

Don't tell anybody, but it's called "polling" not "poling",(https://en.wikipedia.org/wiki/Polling_(computer_science). Polling is done to read the state of connected device(s) which requires digital signal at the port's pin or port. The signal from the circuit above isn't yet any true digital logic. Also you poling ac ringing signal with microcontroller?

In fact, polling is used when you have many digital devices to connected to a microcontroller. You don't need "poling" for simple reading the state on a pin.
 

ravi17

New Member
You have to poll the input to detect the AC.
again, polling is much more involved. polling is word used often to mean monitoring devices continuously like RAM, ROM, DMA, CD drive, PPI devices, input/output devices like keyword, displays etc by the microprocessor. often concerned with devices(memory,I/O devices) which has control signals and exchanges with microprocessor, many times involves interrupt. round robin polling and other algorithm are used. you don't need to say polling word for such simple detection as logic high or low.

Do you actually understand the word polling in the microprocessor and microcontroller? know when to use the word polling? if you mean monitoring pin state, well, that is what anybody would learn in the first microcontroller programming class.
 
Having had a telephone company employee come to my house and cut the wire between my home-made line monitor and the wall I can tell you the telephone companies don't like people drawing continuous DC current from their lines. The central office continually scans the lines looking for persistent leakage. My equipment was drawing only 500 uA when they found and unceremonious disconnected it. Maybe another approach that only sniffed at the lines, drawing a few uA or so would be a better choice.
 

ravi17

New Member
that's right. telco would be concerned after all their battery is draining energy. but also they are i think many equipment out there which needs to monitor the line like modem for example
 

AnalogKid

Well-Known Member
Most Helpful Member
Having had a telephone company employee come to my house and cut the wire between my home-made line monitor
I think we are of an age where that was a common thing among young electro-nutballs. After two such events at home, my parents suggested I wait a month or two between experiments. Bless them, they never even hinted at me stopping, just getting better at it before trying again.
Maybe another approach that only sniffed at the lines, drawing a few uA or so would be a better choice.
M.O.S.F.E.T

ak
 
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