28 December 2014

ears to our world, HumanaLIGHT and the Joule Thief

I was inspired by the recent excellent You Tube video made by W2AEW showing the HumanaLIGHT.

Reference: https://www.youtube.com/watch?v=qfgX93o8HzY

REF: W2AEW  You Tube #187. " A single cell LED light supporting EARS TO OUR WORLD"

Since the money for this kit goes to a noble cause, I decided to buy one. Check out www.etow.org for more information. In the process I also learnt something about the relaxation oscillator and the idea of the Joule Thief. A fascinating journey for me.

Since all is said on the video I thought I would simply record the results of my measurements here on the blog.

First I tried a dead battery that had a voltage of 0.47 volts open circuit. This did not light the LED.

Attaching a variable voltage power supply to the circuit I found that the LED just turns on at 0.8 volts and 'well on' at 1.02 volts.  Full on was measured as 1.74 volts.

Rail voltage was 1.3 VDC for the first three measurements below.

The circuit oscillates at 10kHz. Symmetrical wave form once fully on.

Here below are some views of the scope waveforms.

Output wave form to the LED. 3 volts p-p. Vcc was 1.3 v dc.
Base of final transistor that is connected to the LED. 

Capacitor feedback waveform 

Just turning on with a rail voltage of 0.79 volts

'Well on' rail voltage is 1.02 volts.