Elenco Green Projects - Manual (Page 28)

-27-
50mA
Project #28 Radio Current
Install the battery eliminator connector into the battery compartment in the FM
radio, as shown. Build the circuit as shown, and connect the red and black snap
wires to it. Set the meter (M6) to the 50mA setting and the slide switch (S5) to
position B. Plug the earphones into the radio and place them earphones in your
ears. Turn the volume knob clockwise to turn on the radio, press the reset button,
then press the scan button several times to find a radio station (radio features
may vary).
Listen to the radio and notice how much current it needs. If the sound is distorted,
then recharge the battery using the solar cell or other power sources in this kit.
Use the volume knob to turn off the radio and look at the current measured on
the meter. Even though the radio is off, the current may not be zero. The battery
eliminator is using the remaining current. The radio needs only 3V and can be
damaged by higher voltages, so the battery eliminator has circuitry to reduce
the higher voltages from the power sources in this kit to 3V (for example, the B4
battery is 3.6V, the solar cell can produce 7V, and the hand crank can produce
more than 10V).
Your radio may have a light bulb or LED in it; if so, press the button to activate it.
It may only light dimly, but notice what happens to the current and sound.
Incandescent light bulbs need high current to get bright, much higher than LEDs.
The radio may not work when the light is activated, due to circuitry in the battery
eliminator, which protects the radio from overvoltage. The radio light will work if
you use the radio with normal “AAA” type batteries (not included).
The 470 μF capacitor (C5) is used here to improve
sound quality by helping to stabilize the battery
voltage. The radio needs a steady voltage to produce
good sound quality, but the current it needs changes
slightly as the sound changes. The capacitor can only
supply a small amount of current but can react to
changes faster than the battery can. Remove the
capacitor from the circuit and see if you notice a
difference in sound quality. 50mA
1
Insert eliminator
under belt clip
Press eliminator
down into slot
Slide eliminator
into position
2
3
INSTALLING BATTERY ELIMINATOR
Earphone
plug
Reset
button Scan
button
Volume-on/off knob
Note: Radio style and
features may vary.
See projects 1 & 3 if you
need to recharge the
battery (B4).