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Capacitive touch keyer

This page was last updated : 11-Mar-20 23:09:03

Capacitive touch keyer (ON HOLD)

This project is ON HOLD and shouldn't be build because most of the TTP224 are very sensitive to RF. My first prototype was lucky and worked. I have build 4 adtional one's but they where very sensitive to RF. Even a 10K R or 100uH L it didn't fix it for  15m and down.

I'm working and testing variouce solutions but until then I can't garanty the correct working of the capacitive touch keyer. When you want a out of the box working touch keyer, checkout hamshop.cz and search for "touch".

After a busy week I had to have a "get my mind of the some matters" hamradio project. So I looked in my "nice gadgets and stuff for small projects" and found the TTP224 4- Channel Digital Touch Sensor Module's I bought a few months ago on a hamradio event. 

For working Morse in the field with my FT817nd I only have a cool Spy Morsekey which you can strap on you're leg.

But I'm not that good with straid morse keys and taking my heavy Kent Paddle with my every time isn't a option.  So having build a touch keyer before, I wan't to go smaller, much smaller. :-)

The big advantage of the TTP224N based capacitive touch sensor is that it's only draws 9uA operating (without the leds). So after taking a look at the schematics of the Yeasu FT897D and FT817ND I saw that the use 10K internal pull-ups and 1K blocking resistors which the straid key of paddle pull down to grond to make the Dit's and Dah's. Which is great because I could use that to steal a little of that power and store it for a little while could power the TTP224N for quite a while. So all I had to do is build a small circuit which could store the power but not interfear with the Dit's and Dah's.

Here's the schematic.

In short : the 1N4148 diodes allow some current flow through the 10 Ohm resistors (prevent a large current spike when the capaciters are empty) to the 2 parallel 47uF capaciters.

It takes a little less then 1 sec to get a charge of 2.5V and after aprx 2.4 sec it has a charge of 4V (see : link). With that charge and a draw of 9uA (fully working) it has more then enough energy to last a 21 seconds before the power drops below 2.5 Volt (see : link). Remember between the words there will be some charge again so that time will be even larger.

Here are some pictures of the variouse building steps :

The small Hammond case I bought for this project Euro 2,75.

The TTP224 4 channel capacitive touch sensor $0.99 (search eBay for : TTP224 4- Channel Digital Touch Sensor Module)

To fit it in the case, a small part of the upper right corner has to go. And we want to configure it to be Opendrain (jumper on OD) and active low (jumper on AHLB).

And because of the OpenDrain configuration you have to cut the tracks to the indicator leds (otherwise the will light permenant).

Next is to install a small board connector on which we can place the other PCB.

The Hammond has to have some mods. Remove the 2 screw hols and clean it out.

The circuit build on a small piece of experiment PCB material.

I know it could look better, but hey it works :-)

And it even fits.

Time for some hardware mods. I used 2 M4x10 screws with nuts and cap nuts.

Some soldering . . .

And everthing is coming together.

The cable is half a 3.5mm stereo jack cable I bought for euro 0.99 at the Action.

My 5 cents to the project.

Total cost aprx $5,00 (incl nice Hammond case, metalware, the TTP224N module and the 3.5mm jack cable).

I posted a Video of the keyer on Instagram :  https://www.instagram.com/p/BCya4VaLHOV/

Got inspired and did you build you're own ? Please drop me a mail.

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