[Solved] Reading an Absolute Encoder (Bourns EMS22A)

Using Arduino Sensors
#1

Hey,
I’m having problems reading an Bourns EMS22A Absolute Encoder. It outputs a stream of bitwise data which is controlled by a clock line. you can find the Data Sheet here.
I connected the Pin 6 & 1(chip select & digital input) to ground since I only have 1 encoder and don’t need to daisy chain anything.
Here my test code to test the encoder, but somehow it only outputs zeros and I’m not sure why:

const int PIN_CLOCK = 6;
const int PIN_OUTPUT = 7;

void setup() {
  Serial.begin(9600);
  pinMode(PIN_CLOCK, OUTPUT);
  pinMode(PIN_OUTPUT, INPUT);
  digitalWrite(PIN_CLOCK, HIGH);
}

int last_output = -1;

void loop() {
  delay(1000);
  for (int i=0; i<16; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
    Serial.print(digitalRead(PIN_OUTPUT));
  }
  digitalWrite(PIN_CLOCK, LOW);
  digitalWrite(PIN_CLOCK, HIGH);
  Serial.println(""); 
}

Maybe some one can figure out what I’m doing wrong.

#2

It SAYS you can connect CS to GND but all of the timing diagrams show the sample being taken when you drop CS. :(

#3

On the second page of the datasheet the timing diagram shows that the CSn pin must be high for a minimum of 500ns between readings.

Your datasheet link didn't work, so I'm reading it from a random "datasheet archive" site.

#4

I figured, that the cs pin would only if you daisy chain several encoders together. I tried it anywhy but it didn’t changened anything:

const int PIN_CS = 5;
const int PIN_CLOCK = 6;
const int PIN_OUTPUT = 7;

void setup() {
  Serial.begin(9600);
  pinMode(PIN_CS, OUTPUT);
  pinMode(PIN_CLOCK, OUTPUT);
  pinMode(PIN_OUTPUT, INPUT);
  
  digitalWrite(PIN_CLOCK, HIGH);
  digitalWrite(PIN_CS, LOW);
}

void loop() {
  delay(1000);
  digitalWrite(PIN_CS, HIGH);
  delayMicroseconds(1);
  digitalWrite(PIN_CS, LOW);
  delayMicroseconds(1);
  
  for (int i=0; i<16; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
    Serial.print(digitalRead(PIN_OUTPUT));
  }
  digitalWrite(PIN_CLOCK, LOW);
  digitalWrite(PIN_CLOCK, HIGH);
  Serial.println(""); 
}

BTW: I updated the links in my post above.

#5

Seems I just confused with the wiring, since it works now :stuck_out_tongue:
Thanks for the help anyway.

btw: The ChipSelect pin is realy necessary. Here is my example code in case somebody else wants to tinker with this type of encoders:

const int PIN_CS = 5;
const int PIN_CLOCK = 6;
const int PIN_DATA = 7;

void setup() {
  Serial.begin(9600);
  pinMode(PIN_CS, OUTPUT);
  pinMode(PIN_CLOCK, OUTPUT);
  pinMode(PIN_DATA, INPUT);

  digitalWrite(PIN_CLOCK, HIGH);
  digitalWrite(PIN_CS, LOW);
}


//byte stream[16];
void loop() {

  digitalWrite(PIN_CS, HIGH);
  digitalWrite(PIN_CS, LOW);
  int pos = 0;
  for (int i=0; i<10; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
    
    byte b = digitalRead(PIN_DATA) == HIGH ? 1 : 0;
    pos += b * pow(2, 10-(i+1));
  }
  for (int i=0; i<6; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
  }
  digitalWrite(PIN_CLOCK, LOW);
  digitalWrite(PIN_CLOCK, HIGH);
  Serial.println(pos);
}
#6

Thanks brah - That works perfect!

sepal:
Seems I just confused with the wiring, since it works now :stuck_out_tongue:
Thanks for the help anyway.

btw: The ChipSelect pin is realy necessary. Here is my example code in case somebody else wants to tinker with this type of encoders:

const int PIN_CS = 5;

const int PIN_CLOCK = 6;
const int PIN_DATA = 7;

void setup() {
  Serial.begin(9600);
  pinMode(PIN_CS, OUTPUT);
  pinMode(PIN_CLOCK, OUTPUT);
  pinMode(PIN_DATA, INPUT);

digitalWrite(PIN_CLOCK, HIGH);
  digitalWrite(PIN_CS, LOW);
}

//byte stream[16];
void loop() {

digitalWrite(PIN_CS, HIGH);
  digitalWrite(PIN_CS, LOW);
  int pos = 0;
  for (int i=0; i<10; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
   
    byte b = digitalRead(PIN_DATA) == HIGH ? 1 : 0;
    pos += b * pow(2, 10-(i+1));
  }
  for (int i=0; i<6; i++) {
    digitalWrite(PIN_CLOCK, LOW);
    digitalWrite(PIN_CLOCK, HIGH);
  }
  digitalWrite(PIN_CLOCK, LOW);
  digitalWrite(PIN_CLOCK, HIGH);
  Serial.println(pos);
}

#7

Hi,
reading the absolute data bits works fine with your code! thanks for this!

i am looking at the datasheet and it definitely says:
"
Data Content:
yadda yadda
S4: Increase in Magnitude
S5: Decrease in Magnitude
"

Magnitude means Full Rotation Count right??
When I look at the 16Bit Stream I don’t see a Change in those Bits when rotating!
Am I doing something wrong?

const int PIN_CS = 5;
const int PIN_CLOCK = 6;
const int PIN_DATA = 7;

void setup() {
  Serial.begin(115200);

  //SETUP BOURNS EMS22A
  pinMode(PIN_CS, OUTPUT);
  pinMode(PIN_CLOCK, OUTPUT);
  pinMode(PIN_DATA, INPUT);

  digitalWrite(PIN_CLOCK, HIGH);
  digitalWrite(PIN_CS, LOW);
}


//byte stream[16];
void loop() {

  //READ BOURNS
  digitalWrite(PIN_CS, HIGH);
  digitalWrite(PIN_CS, LOW);

   for (int i=0; i<16; i++) {
   digitalWrite(PIN_CLOCK, LOW);
   digitalWrite(PIN_CLOCK, HIGH);
   Serial.print(digitalRead(PIN_DATA));
   }

  digitalWrite(PIN_CLOCK, LOW);
  digitalWrite(PIN_CLOCK, HIGH);

  Serial.println(""); 

}

In fact there is No Output (0 all the time) on any Status Bit, but i wouldnt know what to do with S1-S3 anyway (Linearity Alarm?)

Nothing in the Datasheet tells me that the Absolute Version has no Magnitude Detection.

I need the Rotation Count, what would be the best/fastest way to get a reliable count?

#8

you might consider a bit shift operation for the reading of the data, something like:

pos = 0;
for(…){
pos <<=1;
pos = digitalRead( PIN_DATA );
…
}

instead of

byte b = digitalRead(PIN_DATA) == HIGH ? 1 : 0;
pos += b * pow(2, 10-(i+1));

#9