Telephone misuse indicator

When the phone line is in idle condition (on hook), the full voltage of 48V DC from the exchange appears across the line. When the phone is engaged by lifting the hand set, the voltage across the line falls down to around 12V. Thus, under idle condition (48V), VR1 is adjusted to give a positive biasing voltage to the base of Q3. As Q3 conducts Q1 gets into reverse bias and stops conduction. If the phone is engaged, Q3 stops conducting due to voltage drop across the lines, and subsequently, Q1 and Q2 starts oscillating and beeping is heard. Thus, this circuit can be used as an indicator for telephone tapping and misuse by an unauthorized person.

Read More

How to use 315Mhz RF transmitter and receiver modules with arduino

Description: This wireless transmitter and receiver pair operate at 315Mhz. They can easily fit into a breadboard and work well with microcontrollers to create a very simple wireless data link. Since these are only transmitters, they will only work communicating data one-way, you would need two pairs (of different frequencies) to act as a transmitter/receiver pair….

Read More

RS485 Shield For Arduino Nano

Arduino Nano RS485 shield will help you to transmit and receive serial data using the twisted pair RS485 network. The module provides half-duplex communication. LED D1 indicates receive data, D2 Transmit LED, J1 jumper is optional and not in use in this application. DI/RE connected to D2 of Arduino digital pin which enables Receiver Output…

Read More