Projects

This car reverse horn can be used with any vehicle having a 12V battery. Transistors T2 and T3 form an astable multivibrator (AMV) that generates beeping tone signals. Medium-power pnp transistor T1 functions as a simple speaker amplifier.BD139 (T4) is an npn medium power transistor. A 5.6V zener diode (ZD1) is connected to its base. ZD1 provides 5.6V DC regulated power supply to the horn circuit built  around transistors T1 through...

Petrol/diesel theft of parked vehicles is quite common. Presented here is an audio-visual anti-petrol theft alarm circuit that can help prevent this crime. The circuit consists of transmitter and receiver sections. The transmitter has to be mounted in the vehicle near the petrol tap, and the receiver in the common room of your house. When someone comes near the petrol tap, you get an audio-visual indication in your room. Fig. 1: Transmitter...
  • Automatic Bathroom Lamp



This simple circuit can be used as an automatic bathroom lamp controller. It disables the bathroom lamp at daytime and enables it at night. The circuit is built around a light-dependant resistor (LDR1), reed switch (S1), two transistors BC547 (T1) and SK100 (T2), a 12V 1-change over (C/O) relay (RL1), a step-down transformer X1 (12V-0-12V, 250mA secondary) along with some discrete components.

The working of the circuit is based on the opening/closing of the bathroom door. When the bathroom door is closed, magnet comes near the reed switch and shorts its terminals. Both transistors T1 and T2 stop conducting, and neither relay RL1 energises nor CFL lamp (B1) glows.

When bathroom door is opened, magnet moves away from the reed switch and opens its terminals. Both transistors T1 and T2 conduct, relay RL1 energises and CFL lamp (B1) glows.
When bathroom door is opened, CFL lamp (B1) remains on. After entering the bathroom do not close the door completely. If the bathroom door is completely closed, lamp (B1) is switched off.

During daytime, lamp operation is not necessary due to the presence of sunlight so LDR1 is used. Fit LDR1 near the bathroom window where it can receive sunlight (reflected sunlight is enough). At daytime if you open the bathroom door, resistance of LDR1 reduces and keeps both transistors T1 and T2 in cut-off state. Relay RL1 does not energise and lamp remains off.

At night, if you open the bathroom door, resistance of LDR1 is high, which keeps both the transistors T1 and T2 in conducting state. Relay RL1 energises and lamp (B1) is switched on. The power supply required to operate the circuit is derived from transformer X1.

Assemble the circuit on a general purpose PCB and enclose in a suitable cabinet. Fix LDR1 near the bathroom window in such a way that maximum light falls on it at daytime. Fix the reed switch on the frame of bathroom door and magnet on the door. Keep the transformer inside the cabinet and place the unit above/near the bathroom door.

  •  Programmable Industrial On-Off Timer With RF Remote


In most of the modern manufacturing and processing industries, there is complete industrial automation through sophisticated hardware and software like programmable logic controller (PLC), distributed control system (DCS), and supervisory control and data acquisition (SCADA). Microcontroller-based embedded systems play major role in industrial automation. One such widely used system is the programmable timer. The major applications of programmable timer are as follows:
1. Initiating the process after de-sired time
2. Switching on/off the process after predetermined time
3. Providing delay in between processes
4. Applying input to on/off type open-loop control system


Fig. 1: Circuit diagram of programmable industrial on/off timer

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