J.F.Drew © 2000-2013

Projects by John F Drew Site map

Mobile menus


Remote control

A project to remote control devices such as antenna selection, fan operation, etc at repeater or beacon sites using DTMF. Creative visitors will think of other applications.

Repeater and Beacon sites are often some distance from those who must  maintain or supervise the equipment. Many of us have trekked up steep hills/mountains or driven large distances in sometimes inclement weather to fix a problem that may well be fixed with a simple remote control. On some sites it may be necessary to switch on fans, swap antennas, or change encoders for telemetry. It’s much easier by remote.

The project described here can exist as a separate project running from a receiver (shared or otherwise) or be integrated into the VK5DJ Repeater Controller.

It began with an idea by Dave Robinson WW2R who produced a remote control board and described it on his site: http://www.g4fre.com/dtmf.htm

I have used Dave’s circuitry, well most of it, and rewritten the PIC16F628A code for a different solution. In the PDF of the circuit forming part of this project I have shown how either the DTMF decoder chip M8870 or the MC145436 may be used. Both work equally well. Dave’s board used a MT8870 DTMF decoder, a 16F84 PIC, a ULN2803 Darlington Driver, a bar LED and a handful of other bits. I use a PIC16F628A and provide an alternative DTMF decoder, the MC145436. The PIC16F628A is cheap and readily available.

The remote control provides 1-7 individual outputs that may be either high or low until intentionally changed or, 1-7 pulsed outputs for periods from 100msec to 4 minutes in 13 steps. An 8 bar LED indicates the output state 1-7 while position 8 indicates PTT function. A CW message is sent after successful control and at this time a PTT function may be used to key a transmitter.

Output state is remembered after a power off/on.

The document file here describes the project in more detail. The HEX file, circuit file and manual is here.

Updated 4 Aug 2014.

Not pretty, but the test setup uses a breadboard with the PIC16F628A, LEDs for checking operation and a loudspeaker for monitoring the tones.

the MC145436 input is on my test repeater board.


See comment below re driving the PIC16F628A with a 8870. I think the MC145436 is a better choice, unless you want to experiment with the drive.

The MC145436 is now obsolete. Perhaps that is telling me something.

Dion, VK7DB, built this version for additional control of his local digipeater. No ULN2803.

George DV2GAP had difficulty getting the 8870 circuit going. This was caused by a software issue resulting from the fact that a MT8870 latches the data to the last digit. This has been overcome in the current version. A 8870 may be used as a replacement for the MC145436 once connections are taken into account.

Here is George’s nicely laid out circuit diagram. NOTE both circuits on this page have an error. Please swap over the wires to the ULN1803 to pins 3/4 and also those to pins 5/6.