For a while I was looking for a paddle for SOTA. Not that I’m any good at CW, but for the day that I might be (and also for practice!) I considered a few different options, but the one I finally landed on was a project developed by David VK3IL. Pressure CW paddle | VK3IL Blog
It has no moving parts, doesn’t require batteries, and you get to build it yourself! A full circuit description is on David’s blog, but in short the paddle harvests some energy from the key lines and stores it in some (relatively) large capacitors to make the pressure sensors work. I ordered some PCBs and was able to put mine together in an evening.
You can adjust the sensitivity by changing the values on some set resistors, or you can add an SMD trimmer. It works great! I just need to figure out how to mount and weatherproof it.
Hi John,
My current solution is not yet waterproof, but I may consider using some silicon sealant.
I first covered the pcb with some clear heatshrink. I then added 2 pieces of closed cell foam sleeping mat material either side of the assembly and used another piece of heatshrink to hold it all together. I simply hold the paddle assembly in my hand, braced against myself or something firm.
Works for me!
Regards,
Peter VK3PF
Hi John,
I’ve gone for a more conventional approach using the same sensors. I have built 3 to date. In over 12 months of operation the only problem has been with a faulty cable. Details are in a recent issue of APC News which can be found at www.mdrc.org.au.
I have used automotive lacquer or clear paint over a completed board for weatherproofing and then boxed it for mechanical protection. Do not paint the pressure pads. For a really impervious coating try the epoxy paint used for cork and timber floors. Two coats will proof it against everything except a Colt 45 at short range.
Glad you like the pressure paddles. I have been using David’s VK3IL circuit board for almost 2 years now on all of my SOTA activations and it works flawlessly. The only time it messes up is OPERATOR ERROR. Hot or cold, wet or dry it just works and no contacts to clean…Ever. As your CW skills progress I’m sure you will love it. Here is a picture of my version I use for SOTA.
Tim - K5DEZ
@VK3IL A rather pedantic comment here, it’s not a pressure paddle it’s a touch paddle. A pressure paddle is something different that uses non-moving force transducers of the type that are sometimes found in joystick controllers. Your design is more correctly called a “touch” paddle.
I’ll have to respectfully disagree here
I’m assuming you’re referring to a strain gauge based design as a pressure paddle.
The sensors used in this design are pressure sensitive resistors with a rather non-linear pressure/resistance characteristic, but still a pressure transducer. In contrast, I would call a touch paddle something that requires no pressure, only touch. These type are typically capacitive and are sensitive to RF interference, which is why I designed this version.
I was in the same thought-space as Colin, I see what looks like a capacitive / restive touch surface in the picture and the phrase “no moving parts” and you immediately assume “touch keyer” which from experience in the damp UK is of limited use outside. However, the resistors are pressure sensitive so must have some movement even if only microns. Had the blurb said “uses pressure sensors not touch sensors” I’d have not dismissed it out of hand.
It is a resistive bridge actuated by deflection an aluminium bar sensible to 100g force maximum.
I use an opamp comparator circuit to turn on an off a MosFet for CW keying.
As I stated in the thread almost 2 years ago it is a “Pressure sensitive” device" and in no way uses capacitance to operate/actuate the keyer. If you were to totally water proof the electronics part of the keyer I guarantee it would still work normally, even under water. If you do some “Google searching” you can see what we mean and physically/scientifically find out how it works. Once you get the sensitivity to your preference they work very nicely. If anyone would like more info on the original extremely simple circuit I made after seeing the article in QST you are welcome to contact me directly. I’m good in QRZ. It only uses a couple MosFets (BS170 or 2N7000), 2 resistors, a battery and the sensors. Or you can check out VK3IL David’s blog and see his Excellent turbo-charged design and circuit board, (which I also use and love) I do not have it water proofed in any way. For me, it is absolutely the best keyer to use for SOTA. Give it a try and experiment. Ya just might like it.
I don’t have many details of these devices as they don’t seem to be stocked by regular parts suppliers, but are readily available on eBay and Amazon. As I understand them they are essentially a sandwich of thin-film resistive material attached to the two metal electrodes. As pressure is applied, I assume that the resistive material is compressed in a manner that reduces its resistance. I’ve attached the response curve I found for the units I used.
The mass market use case for these I believe is controls for consumer devices such as microwave ovens etc.
As it’s pressure based sensing, it doesn’t suffer the issues with moisture and humidity that seem to plague capacitive sensors. It is also more immune to RF interference as the signal voltages are much higher than capacitive sensors.
So far, the field experience with the design appears to be positive.
Hi David,
Is it OK to upload your gerber files to OSH Park and share? Then other people can simply order them as required. https://oshpark.com/
Seems to be a very good service, I used it for the TinySWR and WS0TA tiny traps boards.
Hey David, I’m not sure I totally understand your response curve. It starts out at approximately 7K ohm? All the sensors I have and use and/or researched all start out in the 10’s of M ohm, then when slight pressure is applied then they jump into the 10’s of K ohm. Can you please help me out here. It sounds like you understand these devices much better than I…at least scientifically. As far as RFI, I have never seen it affected in any way, unlike the capacitive ones I tried to build.
Tnx es 73
Tim - K5DEZ
