In the wake of the Covid-19 virus outbreak, many people have found it difficult to keep fit or find the motivation to exercise at home. Consequently, I have designed my product to help the average person keep fit at home.

Overview of design:

Starting at the battery module, it should be powered by a single cell 3.7v battery at your choice of capacity bearing in mind the circuit runs at 500ma. There is an AAP2154OIR1 charge controller and a micro-USB port for charging and a TPS77633DR linear-voltage regulator that regulates for 3.3v at 500ma. Moving onto the micro-controller and architecture, I have used an ATMEGA328PB-AU as it is small but powerful and it is connected to an NRF24L1+ to send data over RF to a receiver to display the data and an ADXL355 (accelerometer) to measure each rep the user performs.

The Enclosure:

The enclosure will be a 3d printed cylinder with clips on each end so it can be clipped onto the bar of the dumbbell or deadlift. I have specifically designed both enclosure and PCB to be as lightweight as possible as to not alter the weight of the exercise item or off-balance it as much as possible.

Ports:

The circuit has a micro-USB port purely for charging the battery and it has an SPI port for programming the microcontroller.

Programming:

The microcontroller can be programmed using the basic AVR libraries and programmed by Arduino as the ISP if desired. There are many libraries for using the RF transmitter over SPI so I have used one of those in the example that I have linked and the accelerometer uses basic analogue outputs that can be read by the ATMEGA in 10bit resolution.

Board design:

I have made the board as compact as possible so it can be clipped over the bar of a dumbbell or deadlift bar with ease and I have used relatively small components to build the board with the exception of the battery port and diodes which I thought more practical for debugging purposes.

The Reciever:

I have also designed a receiver for the project and written my example code based on the architecture of that project however I will not link it here as this is for the transmitter and not the receiver that has a lower complexity level and is only comprised of a microcontroller, 4x7-segment display and NRF24L1+.