Showing posts with label call. Show all posts
Showing posts with label call. Show all posts
Thursday, September 11, 2014
Mobile incoming call indicator
This schema can be used to escape from the nuissance of obile phone rings when you are at home.This schema will give a visual indication if placed near a mobile phone even if the ringer is deactivated.
When a call is coming to the mobile phone, the transmitter inside it becomes activated.The frequency of the transmitter is around 900MHz.The coil L1 picks up these oscillations by induction and feds it to the base of Q1.This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at its output pin (pin 3) to blink.The blinking of the LED is the indication of incoming call.
Notes.
* The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia plastic former.Or you can purchase a 10 uH coil from shop if available.
* The schema can be powered from a 6V battery.
* Assemble the schema on a good quality PCB.
* C1 & C3 are to be polyester capacitors.
* The electrolytic capacitor C2 must be rated 10V.
Tuesday, August 26, 2014
Telephone Call Recorder
Today phone has become an integral part of our lives. It is the most widely used communication tool in the world. Owing to its immense popularity & widespread use, there arises a necessity for call recording devices, which find application in call cent-res, stock broking firms, police, offices, homes, etc. Here they are describing a call recorder that makes use of only a few parts. But in order to understand its working, must first have the basic knowledge of standard phone wiring as well as a stereo plug.
In India, land-line rings primarily use RJ11 wiring, which has wires-tip and ring. While tip is the positive wire, ring is the negative. And together they complete the phone schema. In a phone line, voltage between tip and ring is around 48V DC when handset is on the cradle(idle line). In order to ring the phone for an incoming call, a 20Hz AC current of around 90V is superimposed over the DC voltage already present in the idle line. The negative wire from the phone line goes to IN1, while the positive wire goes to IN2. Further, the negative wire from OUT1 and the positive wire from OUT2 are connected to the phone. All the resistors used are 0.25W carbon film resistors and all the capacitors used are rated for 250V or more.
Subscribe to:
Posts (Atom)
