DIY : Create your first ecofriendly PCB at home

2. Design the electronic circuit

First, I designed the electronic circuit. I tried several online tools but no one satisfied me, mainly because the auto-routing wasn’t optimised. So I finally choosed the free professional software Autodesk Eagle.

PCB shematic made on Autodesk Eagle

The first step was to electronically connect the components. I needed:

  • ILS: This is a magnetic sensor, connecting the input with the output when crossed by a magnet. The variation is watched by the A1 pin of the ATTINY microchip. In use, a magnet was put on the cycling pedal, counting the number of rotations.
  • P$2P$1: A red led, providing light to the sensor IR. In use, a light strip was stuck on the running trainer, changing the luminosity detected by the IR and then changing its resistance. The variation is also watched by the A1 pin of the microchip.
  • ATTINY: Microchip ATTINY85–20PU, a cheap and smaller arduino uno microchip making the interface between the sensor and the bluetooth chip.
  • BLUETOOTH: The big component at the middle of the screenshot. The RX pin is connected to the microchip TX pin, allowing the smartphone to retrieve the microchip data.
  • ALIM: A 5v USB breakout board in order to power the system.
  • PUSHBTN: A push button, in order to be able to reset the system
  • RES: Some resistances

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