Let's Make Robots!

Homemade wheel encoder

Basically I just printed out one of these (laser printer recommended):


...And attached it to a wheel (double sided tape recommended).

Then I hooked up one of these (a 2$ IR sensor: QRB1134):


...And attached it to the motor pointing towards the wheel.

I've been testing it a bit with a few lines of Arduino code and damnit it works :D I'm now able to measure how much the wheel is rotating and therefore calculate how far a robot is moving. I just love it when these cheap lowtech solutions work.

Here are some photos (sorry about the bad quality):





Here is the schematic I used to hook up the QRB1134 sensor:


I used a 0.1uF ceramic cap. Don't know if that's what was intended? It does have a + indicating a polarized cap, but I dunno? Man I wish people would write the kind of cap you're supposed to use, but apparently that's obvious to everyone but me :/ If anyone has a suggestion of what to use I'm open?

Here is the Arduino code I used for testing:

#define IOP 14
#define PWM 3

int val_new;
int val_old;
int clicks = 0;
int turns = 0;

void setup() {
    pinMode(IOP, INPUT);
    val_new = digitalRead(IOP);
    val_old = val_new;

void loop() {
    analogWrite(PWM, 80);
    val_new = digitalRead(IOP);
    if(val_new != val_old) {
        if(clicks == 40) {
            clicks = 1;
            Serial.print("TURNS: ");
        else clicks++;
        Serial.print("CLICKS: ");

        val_old = val_new;

Basically I just add 1 to the variable click every time the color in front of the sensor changes. When I reach 40 clicks I reset the variable click and add 1 to the variable turns. And off course I'm logging everthing through serial for testing. That's it :)

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Looks great, now your robot is getting ready for closed loop speed control and mapping!
Step by step my ideas are becoming reality :)
post code and a schematic on how you hooked it up please :)
Just posted schematic and code used ;)
Looks good but when you reset clicks to 1 you are outputting the clicks variable when you want turns. Minor thing to fix and really only affects debugging ;) Good job I will use this when I make my XMOS and Arduino tutorials using encoders to give me a leg up on doing the code.
Sorry! It's because I changed the variable names from counter1 and counter2 into something more descriptive just before I posted the code. It has been corrected...

You may wanna use interrupts for this sorta thing. I looked into it and found out that this can only be done with pin 2 and 3. Unfortunately my homemade motor shield allready uses pin 3 for motor PWM, so I thought I would try it this way to avoid resoldering my motor shield...

Just thought I'd let you know ;)

PS: Very much looking forward to your X-mos tutorial...

It is going to be a while it will be one of the last turorials and the easy ones wont start for a couple weeks. I want to finish my dagu contest bot first

Actually, any pin can be used as an interrupt -- just not using the "attachInterrupt" function. The newer AVRs support "pin-change" interrupts on any pin. You have to end up delving a bit deeper into understanding the AVR architecture, but there's some sample code in a tutorial I wrote over at TRC: http://forums.trossenrobotics.com/tutorials/how-to-diy-128/an-introduction-to-interrupts-3248/


Forgive me my ignorance but could you tell me what this "one of these" things is ?