I need help with identifying connection scheme of this rotary encoder. I have no datasheet and there is nothing specified on the body except "CTR". Unknown rotary encoder

  • \$\begingroup\$ Do you have a multimeter with continuity tester? or at least resistor test? \$\endgroup\$
    – jippie
    Commented Jan 9, 2013 at 13:50
  • \$\begingroup\$ Does the encoder have detents (click-positions)? If so, how many detents are there for a full rotation? \$\endgroup\$ Commented Jan 9, 2013 at 13:53
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    \$\begingroup\$ How do you expect a rotary encoder to work? The answer to this question will help us explain at the right level. \$\endgroup\$
    – jippie
    Commented Jan 9, 2013 at 14:04
  • \$\begingroup\$ I have multimeter with continuity tester. How does that help? Encoder does have clicks. 20/360 turn. \$\endgroup\$
    – mrkva
    Commented Jan 9, 2013 at 14:12
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    \$\begingroup\$ You can measure the contacts while you rotate the knob. Measure between any of the four pins and slowly rotate the knob and make notes of what happens in which position. \$\endgroup\$
    – jippie
    Commented Jan 9, 2013 at 14:21

1 Answer 1


You need to decide if it is mechanical or optical.

If it is mechanical, you will probably get patterns of pin-to-pin continuity which change as you rotate the shaft. The fourth pin could be unconnected, could be the other side of the contacts, or could be a push-button.

If it is optical, you may get nothing with the continuity tester, depending on the voltage it applies. An experimental LED power supply made of a resistor and voltage source should show an LED-scale diode voltage drop across some pair of pins. Subsequent to that, you may at any given shaft position be able to get one or both of the other pins to sink current supplied through a resistor. You will have to imagine possible internal circuits - for example, a ground pin, an LED anode with the cathode to ground, and two NPN phototransistors with their emitters grounded and collectors exposed.

You can also browse distributor catalogs for a part which looks similar, and see if the indicated data might be consistent in some respects with the part you have in your hand.

EDIT: Just web searching on CTR and encoder finds this very similar appearing part. No data sheet, but it should be enough to figure out the rest with a meter: http://www.tme.eu/at/details/ps1010-20/drehschalter/ctr/ps1010-20-kq15a60-000/

(note: please do not edit to "prettify" this link - there's information contained in the raw URL itself which may be useful if the link breaks)

If you have the circuit it was obtained from, that can provide clues as well - easier to analyze something like this while it is still connected to whatever supplies it needs.

  • \$\begingroup\$ Thanks a lot! The link also provides information, that it is basically just two switches, switching depending on the direction of the turning. Now I have to figure out how I implement it for microcontroller... \$\endgroup\$
    – mrkva
    Commented Jan 9, 2013 at 23:23
  • \$\begingroup\$ You'll find quadrature decoder implementations all over the place if you search. This one is probably course enough that you can poll it instead of needing interrupts. \$\endgroup\$ Commented Jan 9, 2013 at 23:24

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