The user interface on CTR2-Mini is pretty simple. There’s just a rotary encoder and the few buttons built into the Wio Terminal. Normally this works out pretty well, but there are times when you just want to press a button to execute a function, say to send a CW buffer or change keyer speed, for example.

That’s the reasoning behind adding function keypad support in v1.03. I wanted programmable function buttons on my new SO2R controller so I changed the Remote PTT input on the Mini from a digital input to an analog input and built a function keypad using a resistor ladder. The keypad connects to the Remote PTT jack on the back of the Mini (next to the RJ45 jack).

NOTE: This option is not available on Flex-only versions of CTR2-Mini because they don’t have the necessary hardware to support it.

Resistor Ladders

For those of you that aren’t familiar with a resistor ladder, it’s simply two wires with an assortment of resistors and push button switches in parallel. When you press one switch the resistor connected to it pulls the 10K ohm pull-up resistor on the Remote PTT analog input to ground. The Mini reads the resulting voltage change and determines which button was pressed.

It’s very simple, but not foolproof. For instance, if you press more than one switch at the same time all bets are off as to what voltage the Mini will see and what function it will execute (of the programmed functions). Knowing this, just press one button and you’ll be fine.


The schematic for the function keypad is shown below. I used a New Age S3A-401210 enclosure I had laying around but you can build it into anything, even an infamous Altoids box. The buttons are from Amazon but you can use any momentary button you like.

I used a combination of standard 1/4 watt through-hole resistors to build my keypad as shown below. Their combined value should be within 100 ohms or so of the precise values shown.


Construction is not critical. Use whatever you have laying around. What is critical though is that you must use a shielded cable between the keypad and the Mini. Keep it as short as possible. The input to the Wio Terminal is high-impedance so it can easily pick up RF from your transmitter. The 100nF (.1 uF) cap on the keypad and another 10nF (.01uF) cap in the Mini should keep the RF out but if not, toroids are your friends.

Here’s a look at the inside of my keypad. You can install a 3.5mm phone jack in the keypad like I did and use a 3.5mm to 3.5mm jumper cable between it and the Mini. Or, just cut a 3.5mm jumper cable in half and hardwire the bare end to the keypad.

Setting up the Function Buttons

A new Function Buttons menu has been added to the Config menu in the Mini v1.03. This menu displays the five function buttons along with their assigned functions. The 6th button is fixed. It can be PTT or Key, depending on the Rmt setting in the Keyer menu.

To change a function simply click on the menu item for that button and select a new function from the list.

There are 14 functions currently available. You decide which ones you want to use. More may be added in the future if it makes sense. The current functions include:

  • Select from CW messages 1 through 7 to immediately send (message #1 is the repeat buffer – it resends the last message buffer)
  • Open the RIT display (if your radio supports it)
  • Open the Keyer Speed display
  • Open the TxMsg menu so you can select from the available messages (long-pressing the 5-way switch on the Wio does the same thing)
  • Mimic the [A] button (left button on the Wio)
  • Mimic the [B] button (middle button on the Wio)
  • Mimic the [C] button (right button on the Wio)
  • Open the new Antenna Switch Controller menu (in development)

Assigning the [A], [B], and [C] buttons to the keypad allow you to navigate the menu structure from the keypad.

I hope that give you an idea of what this new feature does. I’m not planning on building these for sale because they are simple enough that anyone should be able to put one together. If you have any questions or suggestions please contact me. I’m good on too.

73, Lynn, KU7Q

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