A bit of history behind this project; The kits came about as a result of my own need to have a tidier solution in the shack, over the last couple of years I’ve owned almost everykind of digital modes adapter and always ended up frustrated with either the lack of decent isolocation, the excess of cables needed to get the computer connected and the wasting of a serial port to trigger the PTT. The DigiOne+ gets it name from an idea I had to just have one cable in and one cable out, and whilst its not a complete solution yet ( I’m working on that! ) it is a definate step forward.
The circuit itself is quite simple, I use an off-the-shelf USB soundcard as the heart of the kit so that the only requirement on the computer side is a single USB port. The soundcard works exactly as one would expect, although is not strictly required as one can could extend the audio pads out to another or onboard soundcard, the audio path’s are passed through a pair of isolation transformers and a set of trimmers to permit fine control of the audio levels. Things get a bit more interesting with the source audio line which is fed though an amplifer and rectifier stage to provide a sense input for an ATtiny13A microcontroller in order to control the PTT. I could have gotten away with a much simpler solution but decided to go with a microcontroller to add some flexibility to the kit, in its current iteration the uC provides a configurable watchdog timer to prevent accidental keying up of the transciever, this may seem laughable to some but trust me I have seen software faults do this plenty of times. The watchdog will disable the PTT functionality if a transmission is held for too long, ideal for those of us who operate our stations unattended such as APRS iNodes and digipeaters. The PTT control is terminated via a optocoupler thrus providing complete electrical isolation.
If there is a positive demand for these kits I will consider doing a few more batches, contact me to register interest