This circuit activates a door solenoid for a fixed amount of time, when the receiver picks up a specific coded infra-red signal. The range is up to 8 metres!

The length of time the the solenoid is active can be adjusted using VR1 on the monostable.

Transmitter Circuit Voltage: 9 volts
Receiver Circuit Voltage: 6 to 9 volts
Solenoid Supply Voltage: as required, or Receiver supply

Infra-Red Transmitter/Receiver
Select the required channels using the jumpers on the Transmitter and Receiver - they must be the same.

Link A0 = Ch1,2
Link A1 = Ch3,4
No link = Ch5,6.

Monostable:
Set Range to 2, (0.05-2.5s) with VR1 midway.

The Transmitter sends a coded pulse using Infra-Red light when #1 buttons is pressed (or when #1 input is sent low)

The Receiver picks up the coded signal. If it is the correct signal for #1, it sends #1 output high.

The high signal is inverted to a low signal by the Inverter.

This low signal triggers the Monostable which activates a Relay for a preset period of time - up to 2.5 seconds.
Alter VR1 to change length of the unlock time. If the button is pressed for longer than the Monstable tine, the relay will stay active until the button is released.

• Data Transmission
• Domestic remote controllers

Topics could include:

• Monostables - generating timed events
• Calculating time using T=1.1CR
• Relays and protecting from EMF
• How coils can generate high voltages
• Home Security control systems.

The solenoid can be replaced with any low voltage DC device up to 5 Amps with the relay. This can be applied to a variety of situations.

PROJECT IDEAS

• Remote controlled cat flap
• Remote controlled garage door
• Remote controlled lamp.