Phone Ring Detector

  

Rating: 0.00 / 5 
Inside:
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:

News


  • Craven Herald
    Craven Herald Bowling Club: At the bowling club's annual general meeting, officers elected were: chairman B Denne; vice chairman, P Morton; secretary, A Smale; treasurer, A Morton; president, J Simpson; captain, K Morphet; vice captain, HE Hi
     28 April 2016
  • Mic
    Mic ... faced with this prime example of Drake-ian melodrama, some fans took a more calculating approach to picking it apart. Instead of putting the cover through the of another edit, user @spoker_ looked closely at the photo itself. .... "E
     25 April 2016
  • Kansas City Star
    Kansas City Star He is a dead for “Papa.” Joely Richardson was cast as Mary Hemingway, and Minka Kelly serves as Myers' fellow journalist and love interest. By the time Yari got involved in 2007, Petitclerc had died and several a
     23 April 2016
  • Ottawa Citizen
    Ottawa Citizen “That's a really hard question,” he says by . Then, dipping into his academic background (psychology at McGill University), he suggest that “Music maybe bypasses ... As a busy touring musician, McKhool has car
     11 April 2016
  • RenewAmerica
    Hillary Clinton is currently emoiled in a massive criminal investigation centered on eaches in national security, yet she's inches away from assuming control over our federal law enforcement and national security agencies. Some might call that a
     11 April 2016
  • Beef Central
    Beef Central His demeanor remained the same whether he was talking with a who he just met on a western Queensland property about the season or the managing director of a large pastoral company while he was negotiating the purchase of a thous
     5 April 2016
  • Popular Mechanics
    Popular Mechanics The original version of the , released in 1959, used an external box that had to be mounted on the wall. But that was an annoyance for owners, and so a subsequent redesign inserted an M-type into the itself. This
     4 April 2016
  • The Kingston Whig-Standard
    The Kingston Whig-Standard "Thank you very much for asking that question," the gracious women's star said during a interview to promote her appearance this weekend at WrestleMania 32 in Dallas, Texas. "It's truly been the hardest year of my
     31 March 2016
  • Daily Yonder
    Daily Yonder If I wanted to call Grandma for instance, all I had to do was give a quick short turn of the crank on our home to get Central's attention. That's when she came on the line with a one word question, “number?” That wa
     30 March 2016

.


Leave Comment

characters left: