A simple handpad for focusing

(contents revised Feb 2.020)

All Seletek controllers (original, Armadillo, Platypus and Limpet) support the use of a simple handpad to control the main stepper focusing motor.

To make it more versatile, we have added an optional potentiometer to the design, who will be responsible for setting the motor’s speed. If assembled without the potentiometer, it will be full speed or zero.

Needed items:

•    A small box, almost any small prototype one will do

•    A 1K Ohm linear

•    A 3 position switch (ideally of the “returning” ones)

•    4 wire cable

•    A DB-9 plug (female for Seletek/Armadillo/Platypus – male for Armadillo2/Platypus2/Limpet)



Let’s go with the step by step guide (Correct pin numbers for the Armadillo2/Platypus2 are shown in italics).


– middle pin, to switch’s middle pin (white wire in the image) 

– left (or right) pin to +12v (DB9 female pin 1, male pin 5) (red in the image) 

– remaining pin to neutral (DB9’s chassis) (blue)

3 position switch:

– middle to pot’s middle (white one) 

– one side to pin 6 of female DB9 (green) – pin 9 of male DB9 

– other side to pin 7 of female DB9 (yellow) – pin 8 of male DB9

DB9: … apart from the already shown connections:

– chassis: neutral (blue in the image) 

– pin 1 (pin 5): +12v (red in the image) 

– pin 6 (pin 9): “in” (green in the image) 

– pin 7 (pin 8): “out” (yellow) 

And that’s all. With this small hand pad connected to the “EXP” Seletek connector (only DB9 connecter for the LIMPET), we can operate the motor in a convenient and easy way, maybe with a long cable, or when occasionally doing visual observation, …

It will work with or without a PC, but if we do not want to lose the position tracking (specially if we performed a full calibration), and given that it is the PC program who keeps that information, the PC should be connected so even the handpad movements are tracked (the PC with the Seletek software running!).

One last note: if the PC is connected and active, the speed of the motor will be determined by the PC and not by the potentiometer – this adds to the versatility of the setup.

The final result:


If your prefer, you can buy the handpad ready to use: