Experiment 14: Silicon Amplification
date | aim | safety | method | materials & equipment | results | conclusion
Date
16 March 2010 by Quest 2, to link in with Chapter
14 of our book.
Aim
To use a silicon transistor to make a touch switch to switch LEDs powered
by a silicon solar panel.
Safety
The voltage and current our solar panel was capable of producing posed
no risk of electrocution.
Method
- Test LED arrays with multimeter (on diode test setting) to confirm
polarity.
- Using clip leads, connect the solar panel to one of the LED arrays
to ensure the solar panel and the LED array work.
- Connect an ammeter (on a multimeter) in series with the LED array
to get a continuous reading of the current in the circuit, then position
the solar panel for optimum current.
- Remove the silicon power transistor from its circuit board. Use more
clip leads to connect the transistor in the circuit so that touching
two probes with a finger will make the LED array turn on.
- With the solar panel in a suitable position (we had it on a chair – OK but not in the optimum position), have each
person individually complete the circuit by touching the two probes
with their two hands. See who can produce the greatest current to flow.
- Test with more people holding hands in a loop, with the end two people
touching the probes.
- Connect two LED arrays in series and retest.
Materials & Equipment
- 12 V solar panel (open circuit voltage 18+ volts).
- LED arrays - one 12x 5mm LED 6 V array and one 9x 5mm LED direct
drive.
- Clip leads.
- Multimeter.
- Silicon power transistor.
- Soldering iron, solder, soldering stand, water (for the cleaning
sponge).
Results/Observations
-
The LED array lit up faintly when the multimeter leads were connected
one way but not the other. This made it clear which way around we needed
to connect the solar panel.
-
The solar panel provided the greatest current when held at the window
pointed straight at the brightest portion of the sky. Conditions were
heavy overcast so the sun itself wasn't visible.
-
Maximum current was about 25 mA. The LEDs in the array didn't light
up evenly.
-
When the transistor was first connected in the circuit the LED array
turned on constantly. The base and emitter pins were probably mixed
up, so the leads on those pins were swapped. The transistor switching then worked fine.
Making and breaking the connection (ie, flashing the LEDs) verified
that it was definitely the person switching the LEDs on. When the probes
were contacted directly to each other the LEDs briefly flashed but
otherwise were off.
-
Initially the boys all produced a noticeably brighter light from
the LEDs than Mr Mander (Ian) did. However, with a bit more effort Mr Mander and John
got first equal at 10.7 mA. (That was the total current from the solar
panel, not the amount flowing through the person.)
-
Even six people in a loop conducted enough current to switch the
LEDs on. With a finger on each cheek Mrs Steward had a beautiful smile.
Item Touched With Finger or Hand |
Conductive |
Hand |
|
Fingertip |
|
Nose |
|
Ear |
|
Tongue |
|
Hair |
|
Cheek |
|
-
The switching still worked fine and the two LED arrays drew about
the same amount of current from the solar panel as a single array did.
Conclusion
- A diode tester on a multimeter is useful.
- Solar panels work best in strong direct sunlight.
- Silicon transistors can be used to amplify a very small electric
current and thereby provide a switching action.
- Boys can be very creative in how they connect to each other to complete
an electrical loop.
- The tongue was probably not a good idea with the solder involved.
- A solar panel can output a limited amount of current. By having two
LED arrays connected in series, the solar panel produced twice the
power, and therefore twice the light.
- James officially likes playing with clip leads.
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