Phone Ring Detector


Rating: 0.00 / 5 
Telephone Ringer Circuits / Telephone Circuits
When a phone line rings, there's 90 V RMS AC at 20 HZ on the line. It's enough to give you a jolt you won't soon forget. Thus, it's hard to miss! My favorite detection scheme looks like this. This is off the top of my head so you may have to twiddle component values a bit. Also, this is for driving logic circuits. I'll treat your specific problem in a bit.

Mostly, there is only DC or small signal AC (audio) on the phone line. C1 blocks the DC, and the R3-R2 voltage divider prevents the low level AC from having any effect. When the ring signal comes along (90V RMS) enough voltage is developed at the juncture of R3 and R2 that some charge is pumped into C2 via CR3. Protective diodes CR1 and CR2 ensure that the output of this circuit will not grossly exceed the power supply levels and thus damage the logic circuits it may drive. C2 and R1 have a time constant of 1 second, so one second after each ring ends, the output will fall to a logic zero again. This circuit could easily drive a counter, to count rings. A timer with a longer period could be used to reset the counter if no rings have come in within say 10 seconds. I haven't built this, but here's my theory: C1 blocks DC, R1 limits the current that the ring voltage could cause. The ring voltage is rectified by CR2, filtered by C2, and limited in amplitude by zener CR1. Then the charge stored in C2 is slowly used to light LED1. As long as C2 is large enough (I'd start with 10 uF and experiment from there) to keep the LED on between rings, and small enough that the LED goes off within a reasonable amount of time after the last ring, you're set. For the specific problem in the post I'm answering, (` LED should stay ON while the phone rings`) you would want to change the design somewhat. Here's how I would make a ring indicator light that stays on until the phone acutally stops ringing:

Recommended videos

  • Phone Ringer Circuit
    Duration: 1:18.
  • Telephone intercom circuit with ringer signal generator
    Duration: 1:21.
  • Phone ringer circuit using IC 4060
    Duration: 0:34.


  • The Ringer (blog)
    The Ringer (blog) He posted it in the middle of the Super Bowl — the middle of the Super Bowl — and just … a blurry picture of shoes? A blurry picture of shoes hanging on wire in the middle of the night? A blurry picture o
     25 July 2016
  • Weekly Citizen
    Weekly Citizen Gossard, Geoffrey Alan, 47, 17473, Joe Sevario Road, Prairieville, communications/ Improper language/ Harassment. Roddy, Austin R., 26, 13369 Roddy Road, Gonzales, Simple criminal damage to property, Entry on or remaining in p
     21 July 2016
  • Brownwood Bulletin
    Brownwood Bulletin We would take our homework and kneel on the floor and do our homework so I could watch the plays being rehearsed,” Shores recalled in a recent interview. “Back then there was a couple named Forbes Woods ... As
     17 July 2016
  • Nick's been able to build a unique identity expanding beyond simple toys based on its shows, producing everything from and alarm clocks to sellable slime and more. We're paying homage to Nickelodeon by revisiting some of our f
     15 July 2016
  • Your News Now
    Your News Now You might only expect to see them around the holidays, but in the past couple weeks you've probably noticed bell outside of some local stores. The Salvation Army has with donation buckets, set up at multiple Kewpee restaurants
     14 July 2016
  • Huffington Post
    Even when a lawyer succeeds in setting up a meeting with a detainee, he or she must speak to the client via through a Plexiglass barrier - and the phones are often oken, leaving the lawyer to yell his advice through the Plexiglass. A number of&
     5 July 2016
  • The Business of Fashion
    The Business of Fashion “In wholesale, you would ship to the store and it would be a game of to find out what the customer liked or didn't like.” For career designers who have been burned by the traditional retail system —
     3 July 2016
  • Antiques and the Arts Online
    Antiques and the Arts Online ... Old Porcelain Clocks, Automaton Monkey Clock, Large and Small Swinger Clocks, Bulldog Door , Carved Jade, Quartz, Coral, Turquoise, Amber, Agate, and other Semi Precious Stones, Marble, Onyx and Alabaster and
     29 June 2016
  • The Chattanoogan
    The Chattanoogan We also heated water for the washing machine which was the old "" type. On Saturday morning Daddy ... Of course there was no TV, and our was an eight-party line, so it was no fun attempting to talk to my friends. My nearest
     27 June 2016