INFRA-RED DOOR ALARM

INSTRUCTION SHEET

Transmitter Construction

Inspect the tracks for fine breaks and test the continuity of each track with an electronic circuit tester or ohm-meter.
Identify the four resistors and insert them in the PCB according to the PCB Layout diagram - see Resistors . Solder in place - refer Soldering Technique
The 8 pin IC socket can be pushed carefully into place. Solder in place.
There are two capacitors. Their values are marked on the body, they can go in any way round. Solder in place.
The four PCB pins can be inserted and soldered.
The IR LED can be identified by it's purple colour. Observe polarity and insert and solder,
The second LED is inserted and soldered, observing polarity.
The switch can be located and soldered.
Find the locating DOT on the 555 IC and arrange it as the drawing shows. To fit the 555 it will probably be necessary to bend the legs inwards a little by placing one set of legs on a flat surface and push down lightly. This will maintain their alignment. Repeat for the other side of the chip so they match the socket. Push the IC into place.
The battery snap can be soldered to the pins.
The transmitter uses a 3V power source. The 2 x AA battery holder is used for the transmitter. Connect the batteries.
When the switch is in the ON opsition, the LED will illuminate.

Trouble shooting

Troubleshooting if necessary will involve careful checking of locations and polarity of components, mainly the LED polarity and the locating DOT on the 555 IC is as the drawing shows. Re-solder all joints and check to make sure you have not bridged across between any two adjacent component legs. The end of a broken hacksaw blade sharpened on an emery wheel is a good tool for cleaning between soldered joints.

Receiver Construction

Inspect the tracks for fine breaks and test the continuity of each track with an electronic circuit tester or ohm-meter.
Insert the capacitor and solder.
Insert the transistor observing orientation, solder in place.
Insert and solder the PCB pins.
Locate the switch and solder.
Connect the buzzer wires to the PCB pins.
Insert the IR receiver and solder.
Connect the battery holder to the PCB pins.
Insert the batteries. When the receiver is on, the buzzer will sound.

Setting up

Arrange the transmitter and receiver about 1 metre apart with the IR LED of the transmitter pointing in the direction of the receiver

Orientate the receiver so that the IR decoder is facing the transmitter.

Turn the receiver ON - the buzzer will sound.

Turn the transmitter on and the buzzer should stop. If not check the orientation of both transmitter and receiver.

If you place your hand (or some object) in the beam, the buzzer will sound.

This unit has a range of 2 - 3 metres.

Trouble shooting

Troubleshooting if necessary will involve careful checking of locations and polarity of components. Re-solder all joints and check to make sure you have not bridged across between any two adjacent component legs. The end of a broken hacksaw blade sharpened on an emery wheel is a good tool for cleaning between soldered joints.

Technical notes

Looking at the transmitter, the 555 creates a 50 kHz signal which is used to power the IR LED. This sends a beam of infra-red light.

The frequency of oscillation can be calculated using the following formula:

View the Datasheet for the 555 .

The receiver is primarily made up of the IR decoder. This component receives the IR transmission and converts it back into the 50 kHz signal that was generated by the transmitter - appearing at the Data pin. This signal is filtered by the capacitor which stores enough energy to maintain the status of the transistor in the off position until the next signal pulse (50 kHz - 50 000 times a second).

When the beam is broken, the transistor is energised and the buzzer sounds.

Contact CdS electronics

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