I include photos and schemes to help me describe the assembly. This is a very simple circuit, like you will see.
PD: I also include an origami beating heart, from here
Step 1: Parts
1x 555 timer
1x 27kOhm resistor
1x 3,3MOhm resistor
1x 470nF condensador
2x AAA batt
thin cable (like USB data cable)
1x CD Lens (with coil)
Let's go with the circuit
Step 2: Integrated Circuit 555 Working in Astable Mode
First pic show how you have to connect resistors and the capacitor to enable astable mode operation. where:
C = 470nF
C1= 0.01uF ;this is recomended, but I didn't mount it
RL' sera la bobina de la lente del lector de CDs
RL no va a estar presente.
The second pic show timing graphic and basic equations.
Third pic is the pin description of LM555 timer
Step 3: Boarding
I hate a little island board, but I always use them.
Step 4: Resistive Sensor
In the circuit I have connected Vcc to chasis and 555.7 pin to a aluminium sheet. When you hold the minty box and touch the aluminium sheet the cardiac ritme increase.