# Complete Beginner / Lemon Battery Light

Discussion in 'Electronic Basics' started by Shandy Brown, Jan 7, 2004.

1. ### Shandy BrownGuest

Hey all.

I'm a total newbie when it comes to electronics (more of a software
guy, really). Despite this fact I've decided to do a couple hobby
experiments.

My experiment is basically the classic "electricity from a lemon"
experiment of grade school science fairs. Only, I want the lemon to
light up an LED. Now, I have been told that there wouldn't be enough
energy from a lemon battery to light up an LED. However it was
suggested that one could use a lemon batter to charge up a capacitor
and then the capacitor can be used to make the LED flash.

I have tested the capacitor that I have, and yes, it will make the LED
flash.

Here's the problem: I would like for it to happen automatically
instead of having to manually pulling out the capacitor and touching
it to the LED. Without being completely informed, I went out and
bought a MOSFET, but I have no idea how to use it, or even if this is
the right approach.

The way I see it, there could be two approaches. Either some kind of
timer device that guesses that the capacitor is full and then switches
something, or for the capacitor to send some kind of "I am full"
signal and then switch something.

2. ### Michael BlackGuest

Your solution seems overly complicated and I'm not going to bother

The simples solution is to generate a higher voltage. So you string
the lemon batteries in series, positive to negative terminals, until
you have enough to supply the voltage needed by the LED. Measure
the voltage you get from one lemon, and then determine how many more
"batteries" you need in series to get the needed voltage.

Take note that besides voltage, current is also an important matter. I
have no recollection of what a lemon battery puts out, but if it's not
enough current, then it won't light the LED, even if you do get enough
voltage.

Michael

3. ### MonkGuest

If that is the case try a second string of lemons in paralell to the
first.

And since you're trying to learn basic electronics here's the rule:

Series: Voltage adds up

Paralell: Current adds up

4. ### Michael BlackGuest

I was going to add a bit about that, but figured series connection
was enough for one post.

Michael

6. ### Shandy BrownGuest

Hi again.

There have been some replies to this post. I guess I didn't specify
my requirements strongly enough. The intent of this experiment is
partly to show that the LED can be lit up ("work" can be done) even if
we have a very small energy source, like a single lemon. I am
intending to extend the experiment with a couple different power
sources, including a thermocouple and a radio antenna, both of which I
expect will give me a low rate of energy (I think the correct term is
"current"). I thought I'd start with a lemon as it is the most

Well, actually, I'm starting with the cord to my scanner (12V) so that
I don't have to go through an entire bag of lemons.

So I ask again, does anyone know how to make a circuit that will
switch over to an LED when the capacitor is full? Or perhaps via some
kind of timer?

shandy

BTW: Thanks grahamk for the links. I will look through those pages.

7. ### Sir Charles W. Shults IIIGuest

Yes- check out BEAM robotics- they use circuits that squirrel away tiny
amounts of energy and then use it in a shot- like a solar cell slowly charging a
capacitor and then running a motor for a second or so.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip