Page 1 of 1

Can anyone explain this? (electronics question)

Unread postPosted: Tue Jun 08, 2010 5:29 am
Author: Insomniac
I was messing around with the basic joule thief circuit (the bog standard version, not one of the improved ones) the other day and noticed somthing odd which I can't figure out.

Basically, if I disconnect the negative leg of the LED, and touch it (while not touching any other part of the circuit), the LED dimly lights. If I hold my hand near the toroid while doing this, it gets slightly brighter. It also becomes much brighter if I touch the positive end of the battery with my other hand.

Lastly, if hold the LED in such a way so that both legs are being equally gripped, it still lights.

I'm at a loss as to why this happens... my first thoughts were either some kind of induction or capaciatence causing it, but my electronics knowledge is rudimentry at best so I'm really just blindly guessing. Anyone have any idea what's going on here?

Here's a few pics to illustrate it:

First up, here it is running normally:

Image

Now it's got the negative leg disconnected:
Image

This is what happens when I touch just the negative leg:
Image

And if I touch the positive end of the 1.5V AA with my other hand at the same time:
Image

Lastly, here I'm touching both legs of the LED but nothing else:
Image

EDIT: 1000th post!

Unread postPosted: Tue Jun 08, 2010 5:39 am
Author: chinnerz
WOW YOU MUST BE GENERATING ELECTRICITY!!

But on a serious note, could one part of your circuit be radiating energy?? or could this work on the same principal as touching the aerial connection on a TV with your finger and getting signal, moving you finger 2 cm away and still getting signal?

Unread postPosted: Tue Jun 08, 2010 5:53 am
Author: Insomniac
Well I'll assume energy is being transferred somehow, but in what way is the question.

Unread postPosted: Tue Jun 08, 2010 6:05 am
Author: Technician1002
The circuit has an active component, the transistor to raise the voltage from the 1.5 volt battery to a higher voltage by using the transformer. A green LED generaly has a forward voltage in excess of 2 volts so a single AA battery by itself won't light it.

The AC voltage generated by the transistor circuit with the transformer provides some fairly high voltage spikes. This is coupled through the LED junction (causing the light) on it's way to a large capacitor (you). When you touch a battery terminal, you introduce a resistance (you) to the capacitor so the light becomes brighter. When touching both leads, some of the current meets a resistance where you touch one LED terminal (your galvonic skin response) so some still goes through the LED to find a second path through the other LED lead to this capacitor (you) through another resistance (you again) so there is some light, but not as bright as before.

I hope this makes sense.

When you put together the circuit, it should have had some info on what it does to be able to light a green LED on a single AA battery.

Unread postPosted: Tue Jun 08, 2010 6:14 am
Author: Insomniac
Yeah, I understand the basics of how it works (not what exactly is going on, but I understand that the two coils of the toroid combined with the transistor cause it to rapidly switch on and off at somthing like 20khz, generating a voltage spike as the magnetic field collapses etc etc)

So essentially what's happening is that the voltage is briefly spiking to a high enough level to overcome my skin resisance, lighting the LED as it does so.

Why does moving my hand close to the toroid (not touching) cause it to brighten? Is it to do with the capacitence increasing as a result of a narrower dialectric (air) between me and the circuit?

Unread postPosted: Tue Jun 08, 2010 5:38 pm
Author: jhalek90
here is one for you. i can actually light LED's, with nothing attached to them.

I will post a video soon.

Unread postPosted: Tue Jun 08, 2010 6:02 pm
Author: jimmy101
Insomniac wrote:Why does moving my hand close to the toroid (not touching) cause it to brighten? Is it to do with the capacitence increasing as a result of a narrower dialectric (air) between me and the circuit?

Could be, or your hand is changing the magnetic supseptability around the toroid which in turn is basically changing the toroid's inductance hence changing its oscillation frequency. Kind of like a radio receiver being sensitive to your hand near the antenna.

Unread postPosted: Tue Jun 08, 2010 8:03 pm
Author: Technician1002
Placing a hand on a torrid does little to change it's inductance as you do not influence many of the magnetic lines of flux which is almost entirely in the core of the doughnut. Placing the hand near the coil does increase the capacitive coupling between your hand and the wire on the coil. The effect is capacitive, not inductive.