Wiring up a paddle and straight key

The uBITx requires a Key jack to be wired up (or at least a pull-up resistor installed) before power is turned on.


 It is customary to connect a straight key’s contacts between the tip and shell of the plug and the paddles normally (but not always) have the DOT paddle connected to the TIP and the DASH paddle connected to the RING terminals of the appropriate key jack.

One or two jacks?

A key jack (stereo see-through style 3.5mm connector) is supplied with the kit. You can install one or two key jacks as you wish.  Many install just the one jack since they have a preference for either a manual key or a paddle.  And if you want to switch between key types, Ian Lee KD8CEC’s software make’s it possible to switch between manual key or paddle in software instead of having to wire up two separate jacks.

If you do decide to wire up two jacks, then you will need to buy an additional jack.  All three resistors (4.7K pull-up for straight key to +5v, 2.2K resistor for “dit” and 10K resistor for “dah”) will need to be installed. See circuit diagram below:

Design of the CW keying  

The designer, Ashhar Farhan VU2ESE, in his description on HFSignals.com provides a very good description of how a single analogue port on the arduino nano is used to detect a straight key press, and a “dit” and a “dah” on a paddle.  An analogue port detects the voltage (between 0V and 5V DC) on the pin, and converts this voltage into a number between 0 and 1023. Different values of resistance to ground (with a pull up resistor to give +5V on the pin when no key is depressed) give different voltage readings on the pin and result in different actions being taken by the processor.

This technique is not unique to the uBITx, with many keypads coding 16 or more pins to create different analogue voltage readings for detection by a microprocessor.

Some purchasers have found that they get keying errors, however, with the stock software.  The reason can be two-fold:

  • Dirty contacts on the key not providing a consistent zero resistance path to ground
  • Variations in the actual resistance of resistors supplied with the kit that means the arduino detects a key depression in a different range to what was intended.

Tom Cooper W1EAT used mini-coax (RG-174/U) from the key jack on the back panel of his enclosure to the Raduino and this fixed his keying problem (i.e. no more delayed starts and long dashes and bloopy dits).

A software fix is also available.  Download Ian Lee KD8CEC’s sketch that generally fixes the problem.  The firmware also allows you to determine the actual number value (between 0 and 1023) seen by your arduino nano with a key down, and then allows you to adjust the software thresholds to ensure accurate keying.   The sketch comes with a number of other enhancements.

How to wire up the jack for a straight key

A straight key should be wired so that tip and sleeve will short when the key is depressed.  The sleeve is connected to chassis potential (Earth) and the tip is connected to the blue wire (pin 1 on the raduino connector).    The tip should also be connected to a 4.7k resistor (supplied) with the other end of the resistor connected to the green wire (+5v) from the raduino connector (i.e. the pull-up resistor).

Some folk have wired the pull up resistor directly to the raduino board between pin 1 and +5v DC.

How to wire up the jack for a paddle

Convention has it that the left side of a paddle provides a “dit” and the right side provides a “dah”.  For someone who is right-handed, this means that they will use their thumb to make a “dit” and their index finger to make a “dah”.   It should be possible for a software mod to be added to reverse paddle sides (“dit” and “dah” reversed) for left-handed folk.  Many rigs have this feature.

In the photo, you can see the paddle jack alongside the straight key jack.  The resistors (one end of a 2.2K resistor to the tip for the “dot” and one end of a 10K resistor to the ring) are connected at their other ends to the blue wire.  Together with the 4.7K resistor to +5V they form a resistive divider to ground when a key is depressed resulting in different readings on the analogue port.

Another way of installing resistors for using a paddle

Choke E29AHU has wired in the resistors in a stereo plug adapter (3.5mm to 1/4″) for use with his paddle: