Interface with Littlefuse 55505 Hall Effect Flange Mount Geartooth Speed Sensor

I am trying to get the D21G to interrupt on CH1 with this sensor.

I have 12V input to device on V-/V+

and the sensor being powered by the same lines. then the black and white wire from the sensor going into CH1.

I can't get it to increment the counter when triggering the sensor.

I have tested that the interrupt is working with a jumper from V+ to CH1 and it does indeed increment.

I have also tested that the sensor is putting out a voltage when sensing a metal tooth, it hits about 10Volt when not connected. and when connected to CH1 about 3.8volt

I thought it might be to low of a voltage but i triggered CH1 with a 5 volt input and it worked as well.

Any suggestions or thoughts would be appreciated, thanks.

#include <Indio.h>
#include <Wire.h>

#include <UC1701.h>
static UC1701 lcd;

volatile int counter = 0;

void setup() {

  Indio.digitalMode(1, OUTPUT); //  Clear CH1 to LOW
  Indio.digitalWrite(1, LOW);  // Clear CH1 to LOW
  Indio.digitalMode(1, INPUT); // Set CH1 as an input with interrupt
  Indio.digitalMode(2, INPUT_MASKED);     
  Indio.digitalMode(3, INPUT_MASKED);     
  Indio.digitalMode(4, INPUT_MASKED);    
  Indio.digitalMode(5, INPUT_MASKED);     
  Indio.digitalMode(6, INPUT_MASKED);
  Indio.digitalMode(7, INPUT_MASKED);
  Indio.digitalMode(8, INPUT_MASKED);

  attachInterrupt(8, count, FALLING);       // D8 attached to the interrupt of the expander


void count() {
//  SerialUSB.println("trigger");

void loop() {
  lcd.setCursor(1, 3);
//  delay(100);

Josh Nijenhuis
Josh Nijenhuis
| 2 1 1
Asked on 1/17/19, 12:59 AM

Hi, the INDIO datasheet says we need >11V to trigger HIGH and

on 1/17/19, 2:49 AM

Hi, I'm not sure why you're seeing only 3.8V on the sensor's output when CH1 is configured as INPUT; could you measure the current?

The INDIO datasheet says we need >11V to trigger HIGH and <3V for LOW. 

According to your sensor's datasheet it outputs VDD-2 on HIGH, so that's indeed only 10V. There is an internal pull-up resistor already, but maybe you can try to add an external 1K, to increase the output voltage. When the sensor goes LOW, it would need to supply 12mA to counter the pull-up, which seems within its specs (it mentions 20mA, but also 10.5mA as max). 

| 1 1 3
Answered on 1/17/19, 2:59 AM

It worked to put in a 1K external pull up. Thank you. would be nice if that little tidbit from the INDIO datasheet was in the interrupt section of the software docs possibly.

Josh Nijenhuis
on 1/18/19, 12:19 AM

thanks for the feedback, i added a note in the digital I/O section on github

on 1/18/19, 6:04 AM

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Asked: 1/17/19, 12:59 AM
Seen: 1667 times
Last updated: 1/17/19, 2:59 AM