I ordered a GymBoss workout timer - not as a keep-fit aid but as a timer controller for the VCXO-AXE WSPR transmitter.
W5OLF doesn't provide a lot of detail on how to modify the GymBoss but it isn't difficult - especially if you don't have fuzzy vision, shaky hands and fingers the size of Cumberland sausages. As I have all of those things I experienced an initial panic as I thought I was more likely to break the GymBoss than successfully modify it. Consequently I neglected to take any pictures of the process as I just wanted to get the job done without additional distractions.
Two screws secure the base of the GymBoss. Lift this away carefully as it is secured to the PCB by two short, flimsy and not particularly well soldered wires from the battery compartment. Once the base is clear you can remove two more smaller screws which hold the PCB to the front panel. At this point the pushbuttons will fall out - hopefully you will have made a note of exactly how they were installed so you can put it back together without too much difficulty.
The LCD display rests on the back of the PCB and can be hinged clear to reveal the bottom of the board. The beeper which has to be removed has two connections. The easiest way to remove it I found was just to grasp it between finger and thumb whilst applying the soldering iron to each of the two pins in turn, pushing the board away a bit at a time with another finger until it was clear.
I then soldered a thin screened cable to the two holes that had been used by the beeper. Using my ohmmeter I identified one hole that was at ground potential, so the braid was soldered to that one. I made a small hole in the case near to the "reboot" switch hole to allow the cable to exit. Then I carefully reassembled the GymBoss.
I attached the beeper to the end of the screened cable to check that the GymBoss still worked. To my relief, it did. I then attached a plug to match up with the socket I had already installed for P2 when I built the VCXO-AXE. The braid goes to the ground connection and the beeper signal to the Start pin. I then checked the transmitter with my power meter / dummy load to ensure that the GymBoss was turning it on at the interval I had chosen.
The timer works well and has maintained adequate accuracy for the 12 hours or so it has been running so far. It will start up to 99 transmit cycles at any interval you specify, so you can't have it run indefinitely if you leave it unattended.
As of right now I am running a transmit cycle every 8 minutes using 2 watts into a home-made loaded whip antenna inside the shack using the central heating system as a ground. This has received plenty of spots from Europe and a few overnight from W3HH in the USA which I would not have been able to obtain if I had to key the transmitter manually.
Although manual keying is simple and fine for occasional use, I'm in no doubt that the timer makes the WCXO-AXE much more useful.