I am measuring Dc motor RPM using a rotary encoder(custom made).The input supply to the encoder is 3.3v and the encoder output(Sine wave) is given to the Schmitt trigger to get square shaped signal. I read this signal through a microcontroller for controlling the motor.

I have few question regarding this.

The length of the wire which I use to transfer the signal from encoder to PCB board(microcontroller) is 5 meter.Is this a problem 3.3v signal travelling for 5mts? If so, then I have a 5v supply in the board can I use that instead of 3.3v?

If I am using a 5v instead of 3.3v should I have to use levelshifter(Again Microcontroller uses 3.3v control)?What kind of level shifter can I use for this?

Additional information: Encoder Signal Frequency : 2-5khz

Any idea??


1 Answer 1


As there is very little current involved then the resistance of a few metres of cable is not a problem (voltage drop) BUT it may pick up all sorts of noise. Make sure you use a screened cable.

  • \$\begingroup\$ Thanks@JIm Dearden I will sure do that.I have a doubt on using this screened or shielded cable!!.I have crimp connector on both the end of the wire and if i introduce the shielded cable how will i connect the shied to the ground, should i crimp or any other way?(and the connector will be removed multiple times.) \$\endgroup\$
    – siva
    Commented Jul 20, 2013 at 7:55
  • \$\begingroup\$ I think it is good practice to increase that current through the encoder with small'ish resistors. The encoder is probably little more than a couple switches to ground and the wire will pick up noise when the wire is floating. \$\endgroup\$
    – jippie
    Commented Jul 20, 2013 at 9:10

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