Elenco Green Projects - Manual (Page 45)

Project #64 Cola Light
Project #65
Yellow Cola
When used to measure voltage (5V setting), your M6 has a
high resistance of about 10K
Ω, which is placed in parallel
with the voltage you are measuring. A very small amount of
current will be diverted into the meter, but this will usually
not have any effect on the circuit. However sometimes, if
your voltage source can only produce a small amount of
current, it does change the circuit operation. That is why the
LED can get brighter when you remove the meter from this
circuit.
When used to measure current, your M6 meter has a
resistance of about 500
Ω in the 0.5mA setting and about
10 Ω in the 50mA setting, which is placed in the circuit so the
current flows through it. This meter resistance will reduce
the current it is trying to measure, but the effect will be small
if the meter is set to the appropriate current scale.
Your M6 meter is a simple meter. Normal electronic test
instruments can make better measurements, because they
have less effect on the circuits they are measuring, but even
they have limitations and they can be very expensive.
Replace the red LED (D1) with the yellow LED (D5). Compare the LED
brightness and voltage change to the red LED in the preceding project.
The liquid energy source does not produce enough electricity to run the W1
horn or M4 motor.
The yellow LED needs a higher voltage to turn on
but can get brighter.
If you had pipes pumping fresh cola into the liquid
cells and removing some of the used liquid, then
the LED would stay lit as long as the flow was
maintained - it would be a fuel cell.
5V
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Assemble the liquid energy source using the instructions on page 4. Build the
circuit and connect the red & black jumper wires; the red wire goes to the
copper electrode. Set the meter (M6) to the 5V setting. Fill the compartments
with cola soda (other soda flavors and lemon, tomato, or grapefruit juice also
work). Set the slide switch (S5) to position B. The meter shows the voltage
produced.
Now set the slide switch to position C to connect the red LED (D1). The LED
should be on, though it may be dim. The voltage shown on the meter may be
lower now, because the cola may not be able to make as much electricity as
the LED wants. If you watch the circuit for a while, the LED brightness and
voltage may slowly drop as the cola reacts with the electrodes to produce
electricity.
Remove the meter from the circuit. The LED may be brighter, because all the
electricity produced is going to the LED now.
You can move the copper electrode with the snap on it over to the next
compartment, as shown in the Liquid Battery project. The LED will be dimmer
or not light at all, because the voltage is lower.
If the copper and zinc electrodes get corroded through use, use sandpaper,
steel wool, or a scraper to remove the corrosion and improve performance.
Don’t drink any soda or juice used in this project. Wash the electrodes and
liquid holder.