The same week we got details about the new Apple Watch, my Nike Fuelband died.
That got me thinking about what I really want — and don't want — on my wrist, and whether I could build something that fit my needs exactly.
So expect a few #MakeEveryWeek weeks devoted to iterations of a fitness watch. This is one of them.
My Fuelband had a clock, which I used for timing my midweek runs of about 20 minutes (don't judge). But I had to keep checking my wrist, and pressing a button in the band, to see if time was up.
I really wanted something to simply tell me when 20 minutes was up. So that's what I made.
Step 1: Coding Lessons From a Cat Toy
The ATtiny is like a baby Arduino you program with a mommy Arduino. The steps for that are in the cat toy post. I get the feeling I'll be doing this a bunch more, so I devoted an Arduino Uno to the cause and added a hold-and-release chip holder to my ATtiny-programming setup.
The commands I wanted for this ATtiny were:
- On power-up, Buzz a vibrating motor and flash an LED (just so I know it's working)
- Wait 20 minutes
- Then buzz the motor and flash the LED a bunch
- Sit tight until turned off
Here's the code I used to do just that.
Step 2: Assembling the Pieces
The parts that would end up on my wrist (so not including the mother-ship setup) were:
- An ATtiny85 microchip
- A vibrating motor like those used in phones
- An LED
- A prototyping circuit board, which I cut down with wire snippers
- A battery holder with a switch
- A coin battery
Once I soldered the ATtiny into place, it would be hard reprogram it. So I tested the code — and the buzzer and LED — while it was still in the chip-holder. I'm glad I did. Twenty minutes should be a wait of 1,200,000 milliseconds, but for this ATtiny turned out to be closer to 1,220,000.
Then I popped the chip out of the holder, soldered all the parts together and stuck the buzzer on the back of the battery holder.
Using this chart of the ATtiny pins, the battery power (+) is connected to 5V and its ground (-) to GND. The buzzer is connected to the battery ground (-) and the chip pin marked with a light-blue "4." The LED is connected to GND and the pin marked with a light-blue 0.
Step 3: Into the Wristband!
With an elastic sport wristband in hand, I debated about how best to open it for easy access. It's basically a tube of fabric, and I could add a zipper or a snap or some Velcro. In the end, I just made a 1.5-inch slice into one layer of fabric and slid the electronics inside (shown in the photo at the top of this post).
Step 4: Test Run
This morning, I slipped the band on my wrist, pulled open the hole in the fabric, flipped the switch and went for a jog.
Twenty minutes later the band buzzed against my wrist, and I was done.