This project was made to solve primarily 2 issues I faced while doing pull-ups:

Keeping track of the number of repetitions
Ensuring I pull all the way up

The final outcome was a neat Arduino-based device that uses an ultrasonic sensor to detect the pull-ups, a buzzer that produces short beeps for each complete pull-up, and an on/off switch.

This is an entry to the Exercise Speed Challenge. Also, my first Instructable.

Supplies

HC-SR04 Ultrasonic Sensor
Piezo Buzzer
Pushbutton (Optional)
10K Resistor
Arduino Uno
Breadboard
Jumper Cables

Step 1: Building the Project on a Breadboard

I chose the following connections:

Ultrasonic sensor Trigger-->PIN 6

Ultrasonic sensor Echo-->PIN 9

Pushbutton out-->PIN 2

Piezo buzzer positive-->PIN 10

Step 2: Programming

I recommend you don't change a lot of the code. The top of the program contains the important details, eg: pin numbers, so it's easy for you to change.

The way this works is that when the button is clicked once, the main code starts running and the ultrasonic sensor checks for objects within a distance of 50 cm, and if detected the number of pull-ups is increased and the buzzer beeps. Then when the button is clicked again, the main code pauses and the device remains in standby till switched on again.

pullup_counter.ino
Download

Step 3: Installment

I soldered everything onto a protoboard - you can get one here. You can connect your Arduino to a power supply or use a 9V battery like I did. I also modified a simple recycled cardboard box to keep my components in - i cut out two holes for the ultrasonic sensor and one for the button. Finally, i used blue-tac to stick it on the pull-up bar, but any adhesive will do.