Tuesday, April 29, 2008

Joule Thief Artbots

BatteryBot

A popular circuit for electronic hobbyists called a "Joule Thief" has been making the rounds on the Internet.
When your batteries go dead, there is still energy or "joules" still left in that battery. Instead of simply tossing it out to get recycled, why not squeeze out the remaning joules of life to do something useful.

With the Joule Thief circuit you can light a white led till the battery is down to .2 volts. Use it for a night light, it will run for days. Then, when it is good and dead, give it to the trash collector to get recycled.

2/10 volt and the led is still on!

The circuit consists of a ferrite core with a double winding, a transistor, resistor, led and the "dead" battery for power. Thats all there is. Sure you can put the parts on a perf board and make it work. I wanted more, so I built some artbots with the parts.

Ferrite

Ferrite uses a vintage germanium transistor to be able to run at very low voltages. Like all the way down to .2 volts.



Germanium

Germanium also uses a vintage (1966) germanium transistor. This one is from General Electric. "Ge" is also the elemental name of germanium on the Periodic Table of Elements!

Here is a good modification you can do. Change the 1k resistor to something around 2.2k to 10k and place a CDS light sensitive resistor between the transistor base and emitter (or use a trimmer). This mod will make the circuit light sensitive and cause the circuit to shut down during the day. When its dark , the white led will light. Now how about that for a proper night light!

So go ahead and google "joule thief" and see what you can find, then make your own artbot.


5 comments:

Jay Buster said...

Hello,

Any more specs or part number for that GE germanium transitor?

I'm trying to build a Joule Thief that will use a very low voltage power source (microbial fuel cell).

Thanks!

Watson aName said...

I read the comment on my mostly LED blog, watsonseblog.blogspot.com, about building the Germanium Joule Thief, and also about using a Joule Thief to charge a battery. Here's my blog from last year about using a Joule Thief circuit to convert 1.5V to 9VDC, which would work as well for charging a battery.

http://watsonseblog.blogspot.com/2007/10/this-is-another-dc-dc-converter-from-1.html

_All_ germanium transistors come in a hermetically sealed, usually metal case because the germanium can't be passivated to allow it to be encapsulated in epoxy or silicone. Most germanium transistors have the same specifications, which are a lot lower than silicon transistors. You can buy Ge transistors from a store that has NTE parts (www.nteinc.com), but they're expensive. The NTE102 and part numbers close to that are Ge. Some JFETs will work below 0.6V. The trick is to generate enough voltage -- 3 volts or more -- to switch a power MOSFET on and off, then use the MOSFET to do the 'heavy lifting'. There is a paper on the 'net about a DC-DC converter that works off a thermocouple at 0.35VDC. Best of success.

Botronics said...

The GE transistor is a 2N1307 germanium type.
http://www.digchip.com/datasheets/download_datasheet.php?id=40106&part-number=2N1307

Botronics said...

The GE transistor is a 2N1307 germanium type.
http://www.digchip.com/datasheets/download_datasheet.php?id=40106&part-number=2N1307

Botronics said...

The GE transistor is a 2N1307 germanium type.
http://www.digchip.com/datasheets/download_datasheet.php?id=40106&part-number=2N1307