Organize and Share your Electronics the way you want. Sign-Up for a free account now. It takes only 30 seconds!

Ringing Phone Light Flasher

Ringing Phone Light Flasher

The telephone company sends a ringing signal which is an AC waveform. Although the common frequency used in the United States is 20 HZ and in Europe is typically 25 Hz, it can be any frequency between 15 and 68 Hz.
The most classical telephone ringer circuit is a mechanical bell controlled by an electronic coil. The circut consists of the bell coil and a capacitor (usually 470 nF to 2 uF rated for 250V or more) in series with it. This circuit is connected in parallel to other telephone electronics. The capacitor in the circuit stops the DC in to pass through the bell coil, but it lets the ring voltage through easily. Because of mechanical nature of the ring circuit, it is very sensitive to the frequency of ring voltage and other than the resonance frequency of the bell system (usually around 20-25 Hz) do not generate satisfactory ring.

In computer modems the logical signal from ringing is needed instead of ringing tone. The ring circuit must pass the ring signal information to modem electronics and still provide electrical isolation between telephone line and modem electronics. This ring detection is usually done using one optoisolator circuit, which replaces the raditional ring circuit. The optoisolator output can be easily connected digital electronics, but the optoisolator input side needs more electronics: one capacitor for not letting DC to pass through optoisolator, one resistor to limit the cirrent passing through optoisolator LED and one reverse conencted diode in parallel with optoisolator LED to prevent negative voltages from damaging the LED. This is the basic ring detection circuit.

One modem schematic I have seen used quite special method for detecting ringing signals: It had a small capacitor in parallel with on-hook/off-hook control relay contacts. This capacitor let some small part of the sound and ring signals pass to the telephone transformer. In this way those ring signals can be detected as small signal pulses in transformer secondary (and this circuit can be also used for Caller ID signal detection). The capacitor was so small that the impedance seen from telephone line stays high enough not to disturb other equipments in the same telephone line when modem is no on-line.

Visit Here for more.

 

More Articles to Read

1968 Princeton Reverb Repairs
1968 Princeton Reverb Repairs
Skill Sunday: Power Over Ethernet for Arduino
Skill Sunday: Power Over Ethernet for Arduino
More on Color TFT Displays ~ The Big Ones — 240 X 320
More on Color TFT Displays ~ The Big Ones — 240 X 320
Vertical Pole Climbing Robot
Vertical Pole Climbing Robot
ESP8266 Weather Station Projects
ESP8266 Weather Station Projects
Single tube Lethal Nixie clock
Single tube Lethal Nixie clock
How to make a simple 1 watt audio amplifier (LM386 based)
How to make a simple 1 watt audio amplifier (LM386 based)
Flashing Binaries to DRA7xx Factory Boards Using Device Firmware Upgrade
Flashing Binaries to DRA7xx Factory Boards Using Device Firmware Upgrade
Dot² isn’t your typical coffee table
Dot² isn’t your typical coffee table
Debugging ARM Cortex-M0+ HardFaults
Debugging ARM Cortex-M0+ HardFaults

Top




Shares