There are lots of fidget spinners around at the moment and some are better than others. This gadget uses an Arduino Uno and a infrared LED and sensor to test how good a particular spinner is.
An Arduino UNO A infrared break beam sensor kit Optionally a Display
Note This is how our led and detector looked. Both the IR LED and the Detector need power so hopefully yours each have a red and black wire.
- Each of the two black wires goes to any of the Arduino GND connections.
- The red wire from the detector goes to 5v
- The red wire from the IR LED goes to either 5v or 3.3v
- The 'other' colour wire from the detector (ours was yellow) goes to digital pin 2.
There's a good guide to this by the folks at Adafruit : ir-breakbeam-sensors
There are two versions of the code...
Version 1 : PulseLength_period_v2 This version prints out the Revs Per Second (RPS) every 5 seconds when a spinner is breaking the beam and the maximum RPS and spin down time when it stops seeing a spinner.
Version 2 : PulseLength_period_displayv2 For the second version of the software we used an OLED display and the fantastic u8g2 library. We could tell you how ours is connected but there are so many different versions of the these displays out there the chances are yours will be different. If in doubt, buy your display from somewhere that tells you how to connect it up and use it (our favourite shops are Pimoroni and Adafruit)
We look at two aspects of how good a particular spinner is.
- How fast can it spin
- How long does it take to slow down.
We can use the infrared LED to shine and invisible beam of light at the sensor. This will cause the sensor output to be high unless the beam is broken by the leg of a spinner passing it when it will go low.
To tell how fast its spinning, we use the attachInterrupt statement arrange for the Arduino to stop what it's doing whenever it sees a low on the sensor pin. In the interrupt function ISRPulse() (normally called an interrupt service routine or ISR) we save the current value of a special counter called micros in an array.
As the micros counter gets one added to it every microsecond (uS), when we have been interrupted twice we have the time in microseconds it took between two spinner legs passing by. What we really want though is the frequency with which the legs are passing. The formula that relates time to frequency is Frequency = 1 / Time so if we divide 1 by our time we get the frequency of the legs.
Except.... there are a couple of problems here though...
- The time we have is in microseconds and the formula expects it to be in seconds. So we don't have to deal with a large number (something which micro controllers struggle with), rather than multiplying our time by 1000000 then dividing 1 by that number, we divide 1000000 by our number.
- The number we get is how frequently a leg passes by. This would give us the right number if all spinners had only one leg. To get the correct answer, we assume the spinner has three legs and divide the answer by 3. Perhaps you can modify the code to enter the number of legs.
The rest of the code deals with deciding when there is a spinner present, counting how long its been spinning and when to print out the results.
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Based on an original piece by 2.Times Do CIC at https://github.com/2timesdo/FidgetSpinner