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Telephone Ring Detection

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dramrattan

New Member
Hi,

The 2nd circuit in the link below is what i implemented on breadboard in order to detect ringing. The LED blinks for a short period of time just visible to the eye when the phone rings the first time but for the 2nd,3rd,4th etc rings, the LED does not light or lights very very very faint barely visible to the eye and sometimes not visible at all. What could i do to keep this LED on while ringing is taking place? Or what could i do to make this LED blink visibly everytime for each ring...because i want to be able to count these rings using a PIC18F452?.

Is it to do with the RC combination formed by C2 R2? The values that i used are as follws:

C1 0.1uF,250V
C2 10uF, 250V
R1 10K
CR2 1N914
CR1 Zener 9.2V
R2 1K
LED1 Normal LED (green)

I changed the value of C2 to 33uF,250V but got no lighting of the LED and the voltage across the LED dropped from 1.4V to 0.4V so that was insuffient to light the LED...thus i put back the 10uF,250V capacitor for C2 and changed the 1K to 330 ohm but still the LED only comes on for a very short while barely visible to the eye. What to do?...I am currently reading up on the RC time constant thing hoping to find the answer.

Detecting a telephone RING 1 Electronic Circuit - CircuitsArchive
 

dramrattan

New Member
Ring Detection

Thanks mneary but i switched to the first circuit on that link...When the phone ring, i get a voltage of about 1.6V as the ring detect logic. However, i want to send this signal to be recognised by a PIC18F452 so i would need to amplify it to 5V so the PIC would see it as a logic high when ringing right?...How do i do this?
 

ericgibbs

Well-Known Member
Most Helpful Member
Thanks mneary but i switched to the first circuit on that link...When the phone ring, i get a voltage of about 1.6V as the ring detect logic. However, i want to send this signal to be recognised by a PIC18F452 so i would need to amplify it to 5V so the PIC would see it as a logic high when ringing right?...How do i do this?
hi,
On the version I use the 0.1uf is a 0.47uF and the 100K is a 47K.

Changing these values will increase the drive to the rectifier diodes.

Ideally the circuit should provide isolation fron the phone lines, I use a opto coupler.
 

dramrattan

New Member
Increasing output

I tried using an opto-coupler but couldn't get it to work so i resorted to the circuit mentioned. Would have to buy a 47K resistor and can't get a .47uF with decent voltage...would a 0.47uF 50V work?

Do you have the circuit which worked for you using the optocoupler?...I tried implementing the 4N25
 

ericgibbs

Well-Known Member
Most Helpful Member
I tried using an opto-coupler but couldn't get it to work so i resorted to the circuit mentioned. Would have to buy a 47K resistor and can't get a .47uF with decent voltage...would a 0.47uF 50V work?

Do you have the circuit which worked for you using the optocoupler?...I tried implementing the 4N25
hi,
My ring detector dosnt give a pulse out that you can count.
It uses a unijunction transitor, the cap charges to a preset level then it triggers and pulses a 4N25 opto.
By varying the Res/Cap time constant, it can be made to give an output pulse for a preset number of 'rings'.

The 50V cap you have is to low a voltage, if you have two 100K resistors, put them in parallel for 50K.

OK.?:)
 
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