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When used to measure voltage (5V setting), your M6 has a high resistance of about 10KΩ, 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 changes 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 500Ω in the 0.5mA setting and about 10Ω 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.
It takes higher voltage to turn on the green and blue light
effects than red, so those colors will be dimmer.
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.
PROJECT 36
• Cola Light
PROJECT 37
• Yellow Cola
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 switcher (S6) to the right position. The meter shows the voltage
produced.
Now set the slide switch to the left position to connect the red/yellow LED
(D10). 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.
Replace the red/yellow LED (D10) with the color LED (D8). Compare the LED
brightness and voltage change to the red/yellow LED in the preceding project.
The liquid energy source does not produce enough electricity to run the
melody IC (U32) or motor (M4).
5V