Capacitive Touch Double Paddle

[foggycoder]

As some of you may know, I'm a great admirer of the QSK llc, TP-1 Touch Paddle but it's a bit expensive for me at £190 delivered.

I've been doing some experiments with transistors, partly because I'm trying to learn some electronics and partly because I had this idea to modify my CW Beacon as a touch keyer using transistors instead of relays. Almost by accident, I seem to have come up with this device (images below). It looks too simple to work at all but, amazingly, it works very well!  I've tried it out on Vail and CWCOM and it works without any adjustments to settings.

I already had the two 2N2222 general purpose transistors and the 1000 ohm resistors (they cost pence anyway). And the stereo lead cost £1 (from Kitronics). The rest of it was laying about the Man Cave (the self-adhesive copper tape is used in the garden as a not-very-effective slug repellent).

As I hope you can see, the transistor Base is connected through the resistor to the conductive pad. The Emitters are connected together and go to the earth connection on the "sleeve" of the TRS jack. The Collectors are the output: the left one goes to the "tip" of the jack (dits); the right one goes to the "ring" of the jack (dahs). The touch key jack is plugged into my Kanga K-16 keyer and that plugs into your radio or whatever else you're using to send morse.

You can tell, I'm dead chuffed - for a £1 and a very pleasant hour tinkering at my workbench, I have a very good capacitive touch double paddle.

 

[foggycoder]

UPDATE

The Touch Paddle (my electronics guru is not convinced it's a capacitive touch paddle) triggers my K-16 keyer but only as a single paddle. When both paddles are touched at the same time (squeeze mode) the result is largely random dits and dahs.

Also, the output does not trigger my Morserino. I tried a Darlington Pair on both sides but, whilst the DP worked on the breadboard, I couldn't get it to work on the key itself.

I suppose one can't expect too much from such crude materials. I'll therefore start work on a version with relays instead of transistors. But this has been fun so far.

 

[Ham4CW]

UPDATE

The Touch Paddle (my electronics guru is not convinced it's a capacitive touch paddle) triggers my K-16 keyer but only as a single paddle. When both paddles are touched at the same time (squeeze mode) the result is largely random dits and dahs.

Also, the output does not trigger my Morserino. I tried a Darlington Pair on both sides but, whilst the DP worked on the breadboard, I couldn't get it to work on the key itself.

I suppose one can't expect too much from such crude materials. I'll therefore start work on a version with relays instead of transistors. But this has been fun so far.

I didn't want to say anything before, but your 'guru' is correct.

Touch paddles, or rather  capacitive touch sensors tend to use an HF oscillator to 'drive' the sensor. When you touch the sensor, or even come close to it, some of the energy will be 'robbed' by your fingers/body, causing a drop in voltage on the sensor. This voltage drop is detected and used to trigger the output from the sensor.

Some use another system whereby the sensor pad forms part of a tuned circuit, and the act of touching or getting close to the sensor will alter the frequency of the oscillation, wherein the appropriate circuitry will detect this shift and will again make some change to the output of the sensor unit.

What you have assembled there is more like conduction sensor rather than capacitive. When you touch the sensor plates on your circuit you will be acting as either an antenna, or as a load. Any electrostatic mains hum present will pass through your body, and through the transistors attached to the plates. You could think of the transistors as being open loop amplifiers, so as soon as you touch the plates the electrostatic hum will switch the transistors on and off.

Whether the 'hum' or 'noise' is coming from the unit, the mains, or some other signal being picked up by your body doesn't matter, the effect will be the same. If you ground your free hand to say the case on your keyer you may find it stops working.

In the absence of a true capacitive touch sensor it is still possible to make a simple conduction sensor that will be more reliable than the version you have there, and it would allow for Iambic keying.

We used to use designs like this many years ago for assorted touch switching applications. All you need is some Vero board (copper matrix board), a couple of transistors, and a few resistors.

Make two 'paddles' from the matrix board, with the tracks running horizontally. Connect together alternate tracks so that say, if the strip of Vero was six tracks wide you would end up with two lots of three tracks intermeshed with each other.

On each of your Vero 'paddles' connect one set of strips to the positive terminal of a battery, and on each paddle connect the other set of strips to the base of your NPN transistors via a resistor (this is simply to prevent damage to the transistors in the event of a dead short across the strips).

The emitters of the transistors are tied together like on your version. So now, if you touch either paddle the current from the battery will flow through you fingertips back in to the adjacent set of strips, through the resistors, and in to the transistor bases biasing them on.

There are more 'fancy' versions of this idea, but even the simplified version given here will work fine. If you search the web for "simple liquid detector" or "simple rain detector" you can find similar circuits. The idea being that rain, or any conductive liquid falling between the tracks will switch the transistor on.

I just had a quick look and found a "Raindrop/Snow Detector" on Amazon, and although the sensor circuit is more elaborate, the actual 'sensor' is just a slightly improved version of the matrix board one I outlined above. See here >>>https://www.amazon.co.uk/AZDelivery-Raindrop-Sensor-Module-Arduino/dp/B07CP2GX9P/ref=sr_1_1?dchild=1&keywords=Rain+drop+sensor&linkCode=gs3&qid=1601241105&sr=8-1&tag=78740e-21

If you look closely at the images you can see how the tracks inter-mesh but do not touch. Any liquid across them 'shorts' them out creating a circuit.

In fact, a pair of those Rain/Snow detector units might make for a good, cheap, touch paddle!

Hope that helps.

73, Mark...

 

[foggycoder]

Thanks, G0KZZ. There are some excellent ideas there.

There never seems to be any shortage of things to do. Electronics is just one of several bottomless pits!

 

[foggycoder]

Okay - I've ordered a couple of Arduino-compatible rain sensors. I should be able to use the output to latch a relay. Thinking Cap on.

While I wait for them to arrive, I'll have a play around with vero board.

 

[foggycoder]

After some rather fiddley soldering, the vero board paddles are done. It's only afterwards you realise you could have done it a simpler and neater way. Still, these are functionally correct.

Now I'm waiting for the two relays to arrive. Time to sketch out a circuit.