EXT-ENCODER (U161) proper use & tricky problem

  • Does anyone have any experience using the EXT-ENCODER (U161) to read rotary encoders? When I connect a Type LPD3806-360BM Rotary Encoder, I can accurately count the pulses if the RPM is very slow. When I look at the A and B inputs with an oscilloscope the EXT-ENCODER is adding capacitance causing the leading edge of the pulse to be rounded off. If the RPM is increased, the pulses never reach enough voltage to be counted. Disconnecting the A & B leads removes the capacitance and restores the encoder pulses to a perfect square wave even at high RPM. The EXT-ENCODER schematic shows pull up resistors which are required and they appear to be correct.

    This is the first time I have worked with reading encoders & I need to learn more.

  • @earla said in EXT-ENCODER (U161) proper use & tricky problem:

    The Encoder outputs are NPN Open Collector.
    The Encoder output is active low.
    The signal is normally 'high' and a pulse brings it to ground, 'low'.
    Indeed, the manufacturer says that you cannot see pulses on an Oscilloscope if it is disconnected from the pull up resistors in the sensing Unit.
    This can cause some confusion!

  • @teastain Thank you! Good information.

  • @earla Hello, did you solve that problem with ext_encoder? Iam having same issue with omron encoder , its 2000rpr resolution with A B and Z channels. Iam gettig any readings only if iam spinning it very slowly.

  • @radzieju Could require pull up resistors. Could you provide the part number of the encoder, test wiring schematic and user sketch (program app)?

  • @teastain Hi, encoder is omron E6B2-CWZ6C 2000P/R 5-24v , channels a b z are connected to u161 ext-encoder with 10k ressistors. I tried with and without resistors , also i tried 4.7k.
    pull up ressistors are between channels and +5v.
    M5stickc is powered by usb.I am using uiflow blocks.
    iam trying to measure a lenght of material, it shows a counter values and meter value , but i have to rotate a shaft very very slowly.When i spin a little faster it just stop counting and show same value.

  • Hello @radzieju

    if you look at the schematic there are already pull-up resistors for X, Y and Z. BTW they pull-up to 3.3 V (and not 5 V.)


  • @felmue yes, there are 10k resistors built in into encoder unit i tried with and without them. No good readings.