Published:2011-8-15 20:27:00 Author:Amy From:SeekIC
IR (infra-red) transmitters containing the encoder-IC HT12E from Holtek have been published in Elektor Electronics on previous occasions. The interesting aspect of this design is that the entire IR-transmitter has been squeezed into a handy key ring.
The operation of the encoder IC HT12E has already been thoroughly dealt with in earlier publications. It will suffice to mention here that an address can be programmed on inputs Al through to A8. This address has to be set the same as in the receiver.
On the circuit board, the address lines are connected to ground with a thin piece of track so that address zero is selected. By cutting the track with a sharp knife the corresponding input can be made logic high. This change of address is only necessary when more than one transmitter is active in the same house.
The same story applies to the four data lines, but that is not relevant if you use the IR Multi-Position Switch published elsewhere in this magazine. The generated code is available on pin 17 of IC1, which is modulated with the aid of IC2 on a carrier of 40 kHz. Transistor Tl drives the infrared LED via R4, so that an IR code is transmitted. Two Lithium cells of 3 V each power the circuit. The circuit is only powered when transmit pushbutton S2 is pressed. The life expectancy of the batteries is during normal use more man a year!
The construction itself should be no problem. However, note the height of the components. For this reason an IC socket cannot be used.
A paperclip soldered to the bottom acts as a battery holder, this is ground.
For the top part of the battery holder we use an automotive connector and an M3 bolt.
Because the height of Tl can be a problem when closing the enclosure, the device is best bent flat on the PCB before soldering.