I have been wondering about which key to use with the MTR V2 transceiver while operating portable. I ended up putting a touch keyer together based on the touch keyer module from hamshop.cz. This module is great value and didn’t take to long to be delivered to Australia. The module was mounted in a small project box and the paddles made from single sided printed circuit board. The whole thing only took a couple of hours to put together.
I didn’t want to power it with a battery initially as it would be just one more thing to go wrong in the field, and experimented with powering it by sampling the key out lines to charge a capacitor via some diodes. The current draw by the module is very low. The the key out lines were pulled up to 5V by 1.5k resistors in the radio. The key out lines inside the keyer were diode or’ed together and charged a 470uF capacitor via a 1.5k resistor. This worked ok even under a sustained key for several seconds until the capacitor started to discharge.
This idea was eventually abandoned as the other rigs would have to be modified with the pull-ups in the same way. A lithium CR2032 battery was installed in the end via a switch. I wonder how long it will be until the switch is accidentally left on!
One idea is to make a cover for the paddles, so that when the cover is installed, the cover forces the switch off. I might add a low power flashing led as well.
Anyway, it is working fine and surprising easy to use. Dimensions are 80mm x 40mm x 21mm excluding paddle extensions.