Ring Detector

Blinks a LED when there is an incoming call on a phone line.

Hover over a component to highlight it in the part list.
RJ11 Jack 1uF Capacitor 22K Resistor Diode PC817 Optocoupler 4.7K Resistor LED


A device that blinks a LED when there is an incoming call on a landline. If someone gets a lot of calls, it might get annoying hearing the phone ring constantly. This device provides a silent method of knowing when there is an incoming call. It is also compatible with teletypes. It is far less expensive than the products currently on the market that accomplish the same task. It can be used in conjunction with Microphone.

Part List

Component Description Origin
22K Resistor Prevents optocoupler LED from burning out. Salvaged from PCB
4.7K Resistor Keeps LED from buring out. Salvaged from PCB
1uF 250V Capacitor Blocks DC while letting ring AC through. X10 controller
Diode Single diode rectifier. ATX Power Supply
PC817 Optocoupler Isolates LED from telephone line. ATX Power Supply
Red LED Ring indicator. LED Kit
Front Back Final Schematic Final Schematic (Annotated)


File Size Description
ringdetect.sch 2.9 KB Schematic (KiCad)
ringdetect.pdf 17.9 KB Schematic (PDF)