Cadence Meter Proves Wearable Development Is All About Just Doing It



The tech involved in the fitness world really empowers athletes, whether they’re serious or not, to improve their performance by providing empirical evidence. The Striker project focuses on cadence, which is the frequency of strides when running, or revolutions when pedaling. It uses a force sensitive resistor in the shoe to measure footfalls or power strokes.

The concept behind the device is solid, and there are consumer-grade devices already on the market that are capable of performing the same functions. In fact, a Garmin device is used to help measure the accuracy of the system. But we love to see bootstrapped projects, and this one distinguishes itself not only in finished product, but in the process itself. To us it screams: “What are you waiting for, build a prototype and then iterate!”.

The larger image above shows the earliest working version which is just a piece of fabric that wraps around the forearm to hold a 4-digit 7-segment display. The wire following the arm of the wearer snakes all the way down to the shoe to connect with the force sensor. The image to the right is the first wireless version of the readout. But the project has already seen at least two more versions after this one, mostly using SparkFun components.

We think this is but one example of the kind of stuff we want to see as contenders for The Hackaday Prize. The project uses Open Design and it’s arguably a connected device because the sensor and readout connect to each other (but ideally you’d want to add more connectivy to get at the data). The open nature of the build could lead to leaps forward in the technology by affording talented people wider development access.

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Ask Hackaday: Auto Bed Leveling And High Temperature Force Sensitive Resistors


[Johann] over on the RepRap wiki has an ingenious solution for making sure a borosilicate glass bed is completely level before printing anything on his Kossel printer: take three force sensitive resistors, put them under the build platform, and wire them in parallel, and connect them to a thermistor input on an electronics board. The calibration is simply a bit of code in the Marlin firmware that touches the nozzle to the bed until the thermistor input maxes out. When it does, the firmware knows the print head has zeroed out and can calculate the precise position and tilt of the bed.

Great, huh? A solution to bed leveling that doesn’t require a Z-probe, uses minimal (and cheap) hardware, and can be retrofitted into just about any existing printer. There’s a problem, though: these force sensitive resistors are only good to 70° C, making the whole setup unusable for anything with a heated bed. Your challenge: figure out a way to use this trick with a heated bed.

The force sensitive resistors used – here’s a link provided by [Johann] – have a maximum operating temperature of 70° C, while the bed temperature when printing with ABS is around 130° C. The FSRs are sensitive to temperature, as well, making this a very interesting problem.

Anyone with any ideas is welcome to comment here, on the RepRap forums, the IRC, or anywhere else. One idea includes putting an FSR in the x carriage, but we’re thinking some sort of specialized heat sink underneath the bed and on top of the FSRs would be a better solution.

Video of the auto bed leveling trick in action below.

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