Final project
I would like to make two necklaces that can measure heart rate. The heart rate necklaces can communicate with each other. The heartbeat of the two necklaces will be made visible through each a LED. The values ​​of the two beats will be sent via the 'hello radio' to the other heart rate necklace, where it again becomes visible through an LED. So you can see if both heartbeats are in sync. If not, you both should meditate as long until it does.

Principles of the heart rate sensor with photo diode and infraredlight LED:
The principle of measuring the heartbeat with a light source is based on the transmitted and absorption characteristics of oxygenated and de-oxygenated hemoglobin. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through while deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through. Red light is in the 600-750 nm wavelength light band. Infrared light is in the 850-1000 nm wavelength light band.

This is my first sketch

This is a link to a mind map, which I answer questions such as 'what processes will be used?', 'what parts and systems will be made?' or 'what materials and components will be required?'
mind map

- The first version of the heart rate sensor, I tested with the oscilloscoop with a light sensor (...) and an infrared light (...) (...) showed signals. Unfortunately it was not my heartbeat. It had been just very exceptional as it would operate at once... I decided to add an amplifier, which should enhance the signal. I decided to use the circuit previously found on the internet, because in that example, an amplifier was used.

This is the image
of the circuit
and this is the link: http://www.johnhenryshammer.com/TEChREF/opAmps/opamps.html

voorbeeld circuit

I have used the eagle software to enter the design in order to mill it out on the MODELA later on. The pictures below shows the results of the eagle-software.


Schematic layout


Board layout

versterker back

physical board

At first it did nothing. I could not program the chip. Here came debugging into play.
 1) I checked the soldered and the schematic again.
  - The potential meter was connected wrong in the schematic
  - I soldered the LM358 other way around. I learned more about the different packages of the components.
  - I think I used a wrong capacitor. I probably had misread. Instead of 
0.01 uF I used 0.1 uF
  - At the end I found a missing trace of the voltage regulator. At first I didn't connect the board to the 9Volt battery, but to the external power supply to the header to set the board to 5 volts. I used a oscilloscope to measure its behaviour. Any movement changed the signal, but it was not my heartbeat.

Meanwhile I had a final presentation of the fab academy. Time pressure... I wanted to show something closer to what was my design. I decided to make make my design physically. Sometimes it's better to start all over again. Moreover, you can debug better with separate circuitry. Below is the result.

ketting ring

The circuit I have divided into five parts: The chip, the amplifier, the LED, the sensor and the 'hello radio'.
The board of the chip include connections for the batteries, a voltage regulator and an external crystal and some capacitors and resistors.
The board of the amplifier include two potentiometers and two high pass filters.
The board of the LED include two LEDs and some resistors
The circuit board of the sensor and the infraroodled was made in a ring. I believe the ring would imply less movement. I used copper foil and the vinyl cutter to cut out the circuit. The picture above shows copper foil pasted in the ring and soldered components. This part of circuit include the first high pass filter.

Now debugging really came into play.
I learned more about active high pass filters. The reason ....

fout ligt in de versterker. vermoedelijk is het filter design niet juist. high pass filter is anders aangesloten en gaat meteen van in naar de out.
zie ontwerp
high frequency laat hoge frequenties door. een hartslag geeft .... frequentie
digitaal filteren:
gebruik pin 13 om een potmeter op aan te sluiten die de functie krijgt van als A REF (external voltage reference)
meet met de oscilloscope je hartslag en zet de weerstand van de potmeter op het voltage wat je maximaal hebt gekregen met de oscilloscope. zet in het programma AREF = 1voor de ATtiny 44

Vinyl cutting the traces in the copperfoil

1) Open eagle PNG document in Illustrator and then choose live trace and expand. You can still modify the traces a little. For example, I made ​​the lines a little thicker.
2) Choose print from the illustrator menu: place the object in the lower left corner of the screen. Further operations of the vinyl cutter on the device itself. The width of your file appears in the display.
3) Lift the handle at the back and slide the copper foil under the wheels. The white marks indicate the possible position of the wheels.
3) Navigate through the menu Select roll. The force and speed I used for copper foil 1cm = 60g / s
4) Click OK (PC) to print


Copper foil fresh from the vinyl cutter.

Carefully removing the residual material using tweezers.

Ready to transfer the traces.....
with transfer foil.