Garage transmitter and receiver

Date of completion: 2018

We are lucky enough to have a garage, but we can't see the garage door from the house. To avoid leaving the door open I have installed a simple RF system which indicates indoors whether or not the door is still open. The door has a microswitch set into the frame, which is pressed when the garage doors shut.

Photos

The receiver attached to the bottom of the extractor fan in the kitchen!

Design

Both the transmitter and receiver circuits are powered from mains adapters and voltage regulators. The transmitter uses an LM2936, as this has a smaller dropout voltage than the 7805 used by the receiver. The transmitter has a 555 timer to produce short pulses (about 100 ms) every 3 seconds or so to drive the HT12E encoder connected to the 433MHz transmitter unit (cheaply available with a receiver unit on Ebay). The microswitch setting is inverted by a transistor and sent via the encoder. The receiver unit is decoded by the HT12D chip, which feeds a "transmission received" signal (flash) and the microswitch signal (continuously on or off) to LEDs via transistors to provide the required current (one of the transistors is not really needed - just there for historical reasons!) Each RF unit has a 17.3 cm long vertical aerial, corresponding to one quarter of a wavelength.

Circuit Diagrams

Tiny CAD (.dsn) files:  Garage transmitter   Garage receiver