Assignment I:
Variable Resistance Piano
The first assignment was to build a fancy variable electronic resistor. I built a table-sized piano made of a wet cardboard. The resistance increases with the distance between the cable connection. The internal structure of the cardboard affect on the current.
© Darsha Hewitt
The current flows through a basic 555 timer circuit - creating square wave oscillations which can be played on a speaker. By changing the distance between the connection on the cardboard you can change the resistance and the pitch of the tone.
Assignment II:
The Boiling Water Indicator
The second assignment was to build a fancy electronic switch. I built a construction of a basic 555 timer circuit (creating a square wave oscillation connected to a speaker) which power on/off is triggered by a connection of two contacts. I put the contacts into a water filled glass tube which was set over a flame. Immediately after the water is boiling the expanded water volume let current pass to the circuit.
Final Assignment:
The LED Pulse Sensor
For my final assignment i developed a LED pulse metering sensor. The sensor is made out of a bright LED, a photocell, two 546B transistors, some fixed resistors, a variable resistor (potentiometer) and an array of 9 LED which flash when blood goes to your fingertip.
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The basic principle is the translation of of the human blood flow into an electronic value. The photocell changes its resistance up to the light going into it. The resistance changes if fresh blood comes through your fingertip because of the decreasing of passing light. Two 546B transistors (operation amplifiers) switching the LED array on and of. Up to the size of the fingertip the sensitivity of the photocell (resistance) has to be set with a potentiometer. Due to some experiments and experiences i decided to use a combination of a fixed and a variable resistor (the poti). The variable resistance can be changed from 0-470 ohms which allows a fine threshold setting for the fingertip size.