I have searched the web and cannot seem to find a solution that I can just buy to meet a need I have. I did find a kit online but it is from the UK and I need to get this done quickly.
I have found solutions that are far more complex than what my needs are at the moment.
What I am trying to do is to design a circuit that will identify when a telephone line rings and then trigger a relay to close a contact. I have the first design and build done, but I have an issue everytime I connect the relay.
What I have is 4 metal film capacitors (250V 1µF) in parallele to each other for capacity but in series with the tip side of the phone line. This removes teh DC voltage and provides some torage of the AC voltage when the phone rings.
I then have a full-wave bridge rectifier to convert the AC to DC voltage. I have a 100µF electrolytic capacitor for smoothing and then a 7812 regulator.
Everything works fine. I have 50VAC ring voltage into the circuit, 54VDC out of the rectifier (after the cap) and a solid 12VDC out of the regulator.
When I connect the coil of the relay the voltage drops to 3.3V and is not enough to fire the relay contact. I measured the resistance across the relay coil at 200Ω.
I tried using a 7805 regulator with a 5VDC relay and the voltage when connected is 1.5 volts and I have the same issue of not engaging the relay contacts.
I know that the 7812 should only have 35V on the input, but I have not had any issues (with heat or not having the 12V output) since the load is low current and the interval is 3 seconds.
It has been a long time since electronics classes and I would very much appreciate any help in getting this to work.
I have found solutions that are far more complex than what my needs are at the moment.
What I am trying to do is to design a circuit that will identify when a telephone line rings and then trigger a relay to close a contact. I have the first design and build done, but I have an issue everytime I connect the relay.
What I have is 4 metal film capacitors (250V 1µF) in parallele to each other for capacity but in series with the tip side of the phone line. This removes teh DC voltage and provides some torage of the AC voltage when the phone rings.
I then have a full-wave bridge rectifier to convert the AC to DC voltage. I have a 100µF electrolytic capacitor for smoothing and then a 7812 regulator.
Everything works fine. I have 50VAC ring voltage into the circuit, 54VDC out of the rectifier (after the cap) and a solid 12VDC out of the regulator.
When I connect the coil of the relay the voltage drops to 3.3V and is not enough to fire the relay contact. I measured the resistance across the relay coil at 200Ω.
I tried using a 7805 regulator with a 5VDC relay and the voltage when connected is 1.5 volts and I have the same issue of not engaging the relay contacts.
I know that the 7812 should only have 35V on the input, but I have not had any issues (with heat or not having the 12V output) since the load is low current and the interval is 3 seconds.
It has been a long time since electronics classes and I would very much appreciate any help in getting this to work.