I don’t have any good ideas on where to find SOT23 JFETs at present - the global parts shortage is causing all sorts of headaches!
However, I have just today published a new version of the paddle with a much simplified design that does not require JFETs. You should be able to use the existing PCB with a couple of jumper wires to implement the new design (or you could order new PCBs if you prefer).
The new design uses far fewer components and is therefore even lighter and cheaper than the original. A couple of people have been testing it for the last few weeks and it seems to be working reliably.
Even more EXCELENT work David. The circuit now almost resembles the original one I made except of course you harvested the power from the rig instead of a battery and added a capacitor. I shall have a go at modifying my Version 1 boards and see how they work out. (I only have 20 or so left…Hi Hi)
Thanks,
Tim - K5DEZ
Thanks Tim. Yes, it’s very similar to your original circuit. The capacitor is really only as a preventative against possible RF ingress, so may not be strictly necessary. Modifying a V1 board isn’t difficult (that’s actually how I prototyped the new version). Good luck.
OK David, Thanks and I will get the word out and started giving some of my local friends some of the boards I have. Sure beats installing those super tiny SMD diodes. Hi.
Tim - K5DEZ
I knew my glasses were in need of replacement when I tried to build one of Davids designs using Peters kits. Big fail.
So I took one of my more conventional designs and removed the 9 battery. I connected the anodes of two Schottky diodes to the dot and dash lines and commoned their cathodes. This junction feeds a 470 uF capacitor via a 10k resistor. This adequately operates my 2N7000 fets instead of the 9 V battery. It works fine on a 3 V keying voltage.
I found it would operate down to about 2 Volts. Note that the 2N7000 spec shows some won’t work well at this low gate voltage. However the FET doesn’t have to go full saturation, just to pull the key line below a quarter of a volt or so to key the rig. It’s a 0/1 detection usually. No mA to switch on modern rigs.
So maybe that will help as 2N7000s come cheaply these days.
Edit.
There is a surface mount version of the 2N7000.
Yair it’s an agricultural solution but I grew up on a farm and have half a roll of fencing wire in the garage for odd jobs.
I’m currently using that type of touch paddle in my activities and it works very well, I am also using a special 3D bracket with velcro and I put it around my leg to have my hands free.
73 Manu!
I‘ve built two of those a couple of months ago and also really like them. They work on each of my transceivers except the K1. If anyone is in need of a PCB: I still have some of them and give them away for free. Just write me a message and pick one up here in Dresden or at next year’s Ham Radio in Friedrichshafen. Sending them by mail doesn’t really make sense economically.
