This project has been superseded by my Mk2 version here.
During long periods of DX’ing or contesting a voice keyer becomes a very valuable piece of kit. Some radio now come with one built in and you can always add an external one (see me voice key project) if your radio doesn’t have one. A voice keyer is basically hardware which can save a small message, in most cases a CQ call, which can be sent repeatedly to save the operators voice (and sanity in some cases!).
This article is about my project to add the feature of automatically sending a saved voice keyer message using my Icom IC-756pro3 radio. The IC-756pro3 supports saving 4 separate voice memos and any can be sent using buttons on the radio when in the voice keyer menu which isn’t always convenient as you take up valuable display area, about the bottom 50%, just showing the voice keyer options even though you may only want to send the same saved message over and over.
The IC-756pro3 also doesn’t allow any automatic sending of the messages so the operator still needs to press the button each time they want the message to be sent, not too useful on VHF when you can call CQ for a long time before you get an answer, this menu also has to be open when using the voice keyer from the radio. Icom seem to have thought about this and provide the facility to send a voice keyer memo by shorting one of the MIC pins with a set resistance to ground which doesn’t require the radio to be in the voice keyer menu. Icom even provide the schematic in the manual to make an external voice keyer controller.
This schematic is the basis of my project. What I had to do is present the appropriate resistance on PIN3 of the microphone connector. I achieved this simply by swapping the switches shown with NPN transistors. The transistors were controlled from a PICAXE-20X2 Pic. There were a few design considerations I needed to take into account such as being able to still be able to send a single shot message, be able to do automatic sending with a variable timing between each sending. A simple way to cancel the message if it’s active and a simple way to cancel the auto mode if for example someone replies to the CQ call.
The decision was made to have the PIC control the transistors exclusively and have the appropriate push buttons on the input to the PIC but mapped 1 to 1. In manual mode pressing button 1 would still active T1, the equivalent of S1 and start message 1 on the radio.
For going into auto mode a 5th push button was added which when pressed give the user 5 seconds to choose which message to start sending periodically by pressing the appropriate message button. Once pressed the voice message is immediately sent then resent at the used defined interval based on the position of a variable resistor. The minimal time between messages, i.e. when the variable is at it’s minimal (ADC value of 0) is 5 seconds. This is coded in the PIC code but can be changed. To cancel the user can press any of the buttons on the keypad or press the PTT.