A DIY Smart Insole to Check Your Pressure Distribution
The smart insole collects foot pressure data in real-time. Through Thinger.io the information is fed into a system that visualizes the data.
Pressure measurement is already used in a variety of situations. It provides information about gait mechanics and has a wide range of applications, i.e. in clinical situations and in sports. In this project the sensors are used to gain insight about weight distribution. Real-time visualization of pressure mapping is also incorporated because it makes it much easier to understand your data.
- Arduino MKR1000 – Most 3.3V or 5V boards with Wi-Fi will do the job, but I wouldn’t encourage to use an ESP for this though. For some reason multiple ESP boards returned inaccurate measurements while creating this project.
- Force Sensitive Resistors (3). I used the Interlink 402 (100 N). I’ve also used one more expensive Interlink 406, but in hindsight the 402 would’ve worked too. Use more FSR’s for better accuracy.
- 10K Resistors. Change the resistor to scale your readings to be in the range you want. The higher the resistors, the bigger the increments are. Find more information on this here.
- Accelerometer, I’ve used the 16G ADXL345. Use this to measure acceleration and motion of the foot.
- A soldering iron to put it all together. Alligator clips don’t work well in a shoe for obvious reasons.
Wiring things up
Some quick notes about the circuit:
FSR’s: Read this before you start soldering: be extremely cautious while soldering the wires to the FSR’s. Don’t attempt to do this if you’re not sure if you have the skills. You need to solder it very quickly or the plastic melts. Believe me, I found it out the hard way…
There is no positive or negative side on a FSR, so you don’t have to worry about that.
As I mentioned earlier, you can change the resistors to scale your readings to be in the range you prefer.
Ground/5V: As you can see, all the sensors are soldered to the 5V line and the common.
Accelerometer: You can leave the accelerometer out if you don’t need it for your project. It’s not necessary to use it if you just want to measure the pressure, but it may come in handy if you like to measure acceleration, or if you need to analyze the gait cycle. It’s not strictly necessary for this tutorial however.
Attaching the hardware to the insole
I recommend to do this after running the code first, because if you made any soldering mistakes you’ll find it out at that point. That may save you some hassle attaching and re-attaching the hardware to the insole in case you need to resolder anything.
The FSR’s are attached to three points of the insole. The upper left FSR measures eversion, the upper right FSR measures inversion, and the FSR at the heel measures heel pressure. Finding the right spot for your FSR’s is a matter of trying. The best position to attach them is the spot where the analog value changes the most while walking.
Tape is used to hold the wires in place. If they move, it may cause interference with FSR readings. I’ve also used velcro tape at the bottom of the sole and the inside of the shoe in order to hold the insole in place.
Attach the accelerometer to the back of the heel of the shoe if you use one. I’ve used double sided tape for that.
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