The Maker: Steve Lubbers, Dayton, Ohio Photo of Steve Lubbers

Steve used to develop electronic controls for automotive shock absorbers. Now that this self-described “Enginerd” is working for Bose, his focus is car stereo amplifiers and speaker systems. He relies on the same skills and experience. As Steve says, “We’re still talking about a box of electronics in a vehicle.”

Steve describes how he went about developing this project.

Challenge: Monitor his own heartbeat rate without waiting six weeks to see a specialist.

I went in for a physical and the doctor said ‘Gee, your pulse is really low.’ Normally a pulse is…ballpark…somewhere 60-80 beats per minute. Fifty is low. My pulse is in the mid-thirties! As the medical team was trying to figure me out, they were asking me ‘How low does it go?’ My response was ‘I don’t know.’

I was curious and decided to see if I could figure out how to monitor it. So, I built a gadget to find out.

It’s weird that my pulse is low, but other than the slow heartbeat (bradycardia) I have no other symptoms, no fatigue. I ride my bike for a couple of hours every week; that keeps me in shape.

The Components: Some on hand, some not working, some purchased. 

  • Polar chest strap heartbeat sensor
  • Adafruit RF pulse receiver
  • Wave form generator
  • Arduino Uno
  • SD card writer
  • Red LED
  • LCD display
  • Buzzer
  • Battery (phone charger)
Project schematic

DIY Heartbeat Monitor Project Schematic

The Polar chest strap sensor was given to me. Years ago, magazines and chip makers would have contests. They would give you stuff and say “Build something.” Parallax called the contest microMedic. They wanted medical-related projects. I didn’t use the chest strap at the time. But when I started thinking about my own project…I remembered somewhere I have a box with a heartbeat monitor system. I went digging and pulled out that chest strap, found out the battery was dead, and then had to figure out how it worked.

The Polar strap is RF and just sends a pulse.

Then I found that Adafruit sold that little green board [lower right] that received the RF pulse and converted it to a digital output signal.

Adafruit actually sells the entire kit with everything from Chest Strap to a blinking LED that accompanies the pulse.  After I found the kit on Adafruit, I didn’t have to reverse engineer the RF signal because I could use the little circuit board that received it. I wish I found it before I repaired my chest strap.

I ultimately bought their entire kit, because – why not?   

The white component with the dials is a wave form generator. When I was debugging code, the wave form generator acted as a simulator to let me control the pulse input rate of the signal going in. Otherwise, I had to run in place to get my heart rate up. And sit down to get the heart rate down.

The Arduino Uno is hidden under a shield. The shield is an SD card reader/writer. The Arduino counts the pulses and writes them to the SD card so I can record them and look at them later.

Electronics on a Phase Dock WorkBench

DIY Heartbeat Monitor

At first, I used a red LED that pulsed with my heartbeat, but that was too simple. I added the LCD display as a real-time readout to show the pulses, or to show a little bar graph with a target rate and where I am with respect to that.

I added the buzzer relatively early on when I was experimenting and debugging. I found that if I moved too far away from the receiver, I didn’t have a signal anymore. So as a way of notifying me that I’d gotten too far away…sort of like when you flat line…when your pulse goes to zero…the thing would squeal at me. Adding the wave form generator made things easier.

Building, troubleshooting, and deploying the project:

I should pull the Phase Dock WorkBench out when I start building things, but generally all the stuff that is now on the WorkBench was just scattered across my desk.

Isn’t that how we all start?

I had a problem with the Polar strap because it had been in the closet for years. So, the WorkBench came in handy when it was time to figure out “what’s not working? Is it the transmitter? Is it the receiver?” because I had wires and things everywhere.

When I finally put the project together on the WorkBench, not only did it look nicer, but it was also stable. Then I could finally figure out what was really broken.

Building the heartbeat monitor on the Phase Dock WorkBench also solved the problem of my being able to move around and still collect data. Unless I wanted to sit in a chair all the time, with the project on a table next to me, I needed to have all the electronics mounted and transportable.

I mentioned I’m a cyclist, right? I put the Cover on the WorkBench, mounted it on the back of my bike and took it for a bike ride. It’s battery powered. I’m wearing the transmitter. It’s all nice and contained back there.

When I get home, I can see that when I ride the bike my pulse goes up. It’s supposed to do that, right?

Heartbeat Monitor on the Bike

Thanks for sharing, Steve!

Steve is a long-time user of the Phase Dock WorkBench project development system.  You can find two other projects that Steve shared in our Inspiration Gallery: