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Definition: Selcall
Definition: Telcall

DT8R - DTMF controller board (relay)
DT8T - DTMF controller board (transistor)

Note: DT8T is no longer available - details for information only.
We still sell the DT8R with 8 change over relay outputs.

Click for photos Click here to see photos

The DT8 DTMF controlled relay board is available in two versions:
DT8R - with eight single pole double throw 3A relays
DT8T - with eight open collector transistor outputs (100ma 30v max)

The DT8 DTMF controlled relay board has been designed to offer a simple remote control facility which can be used over both land-line and radio links. Each of the eight relays can be programmed for operation in one of four modes: Follow, Pulse, Latch or Exclusive. See HERE for operational commands.

In Follow mode a relay (1 to 8) is operated when the appropriate tones are being received and then the relay releases when the tones stops. DTMF 1 operates relay, DTMF 2 operates relay 2, etc, up to DTMF 8 operating relay 8. DTMF 9, 0, * and # are used for special functions (see below).

In Pulse mode a relay is operated as soon as it's DTMF tones are received and stays operated for a time determined by the programming. The pulse time is retriggerable, ie. sending the DTMF tones again resets the timer for that relay. Note that the pulse time is measured from when the DTMF tone is first recognised - holding the DTMF tone on continuously will NOT alter the length of the pulse.

In Latch mode a relay can be turned on and off be sending DTMF tones. To turn ON a relay send a DTMF code followed by *, eg. sending 8 * turns on relay 8 (if relay 8 is already turned on then this command does nothing). To turn OFF a relay send a DTMF code followed by a #, eg. sending 8 # turns off relay 8 (if relay 8 is already turned off then this command does nothing). Any relay in Latch mode can be programmed to turn on at power-up or Restart (see below).

In Exclusive mode a number of relays can be programmed to operate exclusively, only one relay can be operated at any one time. Relays are switched ON by sending the appropriate DTMF code any exclusive relay that is already operated is released. For example if relays 1, 3, 5 and 8 are all programmed to be exclusive and relay 3 is operated then sending the DTMF 5 would switch relay number 5 on and release relay number 3. Any relay in Exclusive mode can be programmed to turn on at power-up or Restart (see below).


There are a number of special commands available: Lock, Unlock, All On, All Off as described below.

A Lock code can be programmed into the unit if required to disable operation of the DT8. The lock code can be between 1 and 8 characters in length and any characters 0, 1 to 9 or A to D can be used (* and # are not allowed) giving a total of over 1500 million exclusive lock codes.

An Unlock code can be programmed either to be the exactly the same as the lock code or to be entirely different. The unlock code is used to re-enable the DT8. The unlock code can also be between 1 and 8 characters in length and any characters 0, 1 to 9 or A to D can be used (* and # are not allowed) giving a total of over 1500 million exclusive unlock codes.

All On can be used to turn on all the relays at the same time. Because this command could cause potential problems it has to be specifically enabled in programming. The All On command is DTMF 0 *.

All Off also has to be specifically enabled in programming. The All Off command has four possible operating modes selectable by programming:

1) Disabled - do nothing
2) Reset All - reset all relays to off
3) Soft Restart - This sets the relays in the normal power up state
4) Hard Restart - This is basically a system reset where the DT8 software is restarted

The All Off command is DTMF 0 #.


The DT8 has an auto-lock feature that will automatically lock the unit after a certain amount of time. There are three options for this feature: OFF, IMMEDIATE and TIMED. The OFF option disables the auto-lock feature while the IMMEDIATE option means you have to enter the unlock code then immediately follow with a command code. The TIMED option allows you to set a time betwee 0.1 and 9.9 minutes after which the unit will be locked. The timing starts from when the unlock code is entered and is restarted after every entry. This means that the auto-lock time out period is from the last entry you made.


As well as the normal operating mode three special access codes are available. They are INDIVIDUAL, GROUP and ALLCALL access codes. Each of these codes require the sending of two digit DTMF codes before the command codes are sent. When using GROUP and ALLCALL Access modes no Audio Feedback is produced and multiple units can share the same codes. GROUP and ALLCALL access codes allows control of multiple units at the same time. When using INDIVIDUAL access codes the DT8 will produce Audio Feedback tones if enabled. Only one unit should be allocated any one INDIVIDUAL access code. Individual LOCK and UNLOCK Codes still work but AUTO-LOCK IMMEDIATE should preferably not be used.


AUDIO FEEDBACK is enabled by a programming sequence. When AUDIO FEEDBACK is enabled the microprocessor keys a PTT control transistor (open collector) so that the DT8 may be used with a radio transceiver. Using the AUDIO FEEDBACK feature slows down the operation of the DT8 as acknowledgement tones and PTT signals are generated and transmitted after each tone or command is received.

There are several tones used:
First is the input acknowledge tone (a high pitched tone). This tone is produced after the end of each input tone (unless an error, action acknowledge or off tone is sent, see below).
If an error is detected then the error tone is produced (a low pitched tone) or if an relay OFF command is received then an off tone is produced (a medium pitched tone).
When a special command is received by the DT8 (such as ALL ON, ALL OFF, LOCK CODE or UNLOCK CODE) then the command acknowledge sequence is produced. This consists of three pulses of a high pitched tone.


Programming mode is enabled by placing a link on the DT8 board. A piezo alarm gives positive feedback for key entries. Most programming codes are of the format * n n n n # where n is a digit from 0 to 9. See HERE for programming commands.

Click here for the DT8R/DT8T manual


Supply voltage:

Nominally 13.8volts DC
approx 320mA max (all relays on)
approx 10mA idle


Via screw terminals.
Common, Normally Open and Normally Closed for each relay (DT8R)
Collector connection for each transistor (DT8T)
Power & Ground.
Signal in, Squelch (COR) in & Ground
Audio feedback output, PTT and Ground

Auto-lock timer Off, Immediate or 0.1 to 9.9 minutes in 0.1 minute steps
Pulse timer periods:

0.1 to 9.9 Seconds in 0.1 second steps.

Switching capability: Relay contacts - 3A maximum per relay.
Open Collector - 800mA 30v maximum
PCB Size:

5.1 in Wide, 4.35 in Deep, 0.8 in High
130mm Wide, 110mm Deep, 20mm High
Box Size:

5.5 in Wide, 4.35 in Deep, 1.35 in High
140mm Wide, 110mm Deep, 35mm High

Jenal Communications design and manufacture a wide range of radio related devices including units which use the standard HF selcall and telcall signalling as used by Barrett, Codan, Icom and Q-Mac. Thousands of these products are being used all around the world by Governments, NGOs, Commercial organisations and Amateur Radio operators. We also manufacture a number of devices which use the common DTMF (or touchtone) signalling system.
Last modified: 23 June 2015.