Phone Line Ring detection circuit
FlyingFishFinger
Posts: 461
Hello!
I'm doing a science fair project that involves phone line communications. I'm using the circuit from the NV #19 to interface the phone line (or I plan to, once I get the whole thing thought through) and require the Stamp to be able to "answer the phone". Now, I found the following circuit: http://www.tkk.fi/Misc/Electronics/circuits/ringer.gif
which allows me to logically detect a ring on the line. However, I need to know if this circuit will indeed work (If I put it in parallel with the one from the NV column and use the relay to switch between the detector and the communicator) and if so, what values I need to use for the Zener diodes.
Thanks in advance
Rafael
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You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
I'm doing a science fair project that involves phone line communications. I'm using the circuit from the NV #19 to interface the phone line (or I plan to, once I get the whole thing thought through) and require the Stamp to be able to "answer the phone". Now, I found the following circuit: http://www.tkk.fi/Misc/Electronics/circuits/ringer.gif
which allows me to logically detect a ring on the line. However, I need to know if this circuit will indeed work (If I put it in parallel with the one from the NV column and use the relay to switch between the detector and the communicator) and if so, what values I need to use for the Zener diodes.
Thanks in advance
Rafael
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
284 x 215 - 2K
Comments
At some point you are going to have to look at the reality of the numbers and the ring voltage.
That schematic is intended to be used with an SX-28 Caller ID program, but you could eliminate the 600 ohm transformer and have a direct connect to a phone instead. [noparse][[/noparse]This phone will still ring and have to be answered by a human. You might want to do something else.]
In that diagram, the zeners are 22volts each. I am not sure if 1/2watt will be enough. You can try and if it self-destructs, just redesign. It seems that they might not work as the 10K resistor is limiting the possible 150VAC ring [noparse][[/noparse]150/10,000 = 15ma]. Quick figuring seems to indicate 2.25 watts. I may be wrong. The 150VAC is a worst case and regional differences can go much lower [noparse][[/noparse]24VAC].
You could build it all with 1/2watt components and just put in an appropriate fuse to avoid damage, but it is hard to get anything less than a .250amp fuse. {I am figuring 15ma @ 150VAC peak-to-peak = 2.25watts]
If you increase the resistor size by 5 times, you reduce the wattage to 1/5th. That might work.
The www.sxlist.com site will refer you to a site with much more in depth discussion about telephone interfaces and ring detection.
The·Ring Detector·is a neat little device when used with the Caller ID to re-route only certain telephone numbers or to have only certain telephone numbers trigger a robotic device, but I don't think a BasicStamp can easily do that. I was thinking of a dog food feeder that would only respond to my cell phone number. All other calls would just be handled normally by my answering machine.
AND ABOVE ALL, the Ring Voltage can give a nasty shock. SAFETY FIRST.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 11/15/2006 2:14:52 PM GMT
And also, where would I find the numbers and ring voltage you metioned for SoCal?
Basically what I want to do is have the Stamp sit on the line listening for a call, if it gets one, recieve it and then do stuff with the data that come through the line (I have a DTMF decoder on the Stamp side, which works fine).
Thanks
Rafael
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You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
http://www.sxlist.com/techref/pots.htm >> POTS = Plain Old Telephone Service
Then Try "Phone Line Interfacing" for the schematic
I am sorry, there is quite a bit of reading there.
I have a print out that is good - Telephone line audio interface circuits' by Tom Engdahl.
It is at·http://www.tkk.fi/Misc/Electronics/circuits/teleinterface.html, but I had to use a Google search to get into the web site.
The same author has a seperate site for Ring Detection that has your schematic with component values and more.· You can build a nice ring detector with a bridge rectifier that is quite sturdy.
You can build your own DTMF decoder with an SX-28 too!
I suspect that the hardwire values are all the same for the U.S.A. [noparse][[/noparse]one standard].
The key component is a 600ohm to 600ohm transformer. I bought 3 for about $1 each recently. You can work without them, if you must. But they are intended to provide isolation and safety.
Telephones are an unusual mix of AC and DC. Quite interesting as Engdahl's article explains it clearly. He also explains how 4-wire duplex goes to 2-wire hybird and various reasons for poor quality sound.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 11/16/2006 10:20:29 AM GMT
What interface do you think is better in terms of doing the job? I'll probable end up doing both as a comparison for the project anyway though.
The thing is I don't want to place several small orders from Digikey/Jameco. I'd rather wait till I have enough info to get one bigger one with all the stuff I might need for the project.
Thanks
Rafael
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~