Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 37)

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Make sure you have a strong 9V battery for this
experiment. Connect the wires according to the Wiring
Checklist, connecting the wire to the battery last since
this will turn on the circuit. And be sure to disconnect this
battery wire when you’re not using the circuit to avoid
draining the battery. This time you will measure 9V
batteries, just like the one you are using to power your
Electronic Playground. Take two long wires and connect
one to spring 26 (ground) and spring 43 (3.3K
Ω). When
you are ready touch the other ends to the battery you
want to test, being sure to connect them to the positive
and negative battery terminals as shown in the
schematic. If LED2 is bright and LED1 is off then your
battery is good, otherwise your battery is weak and
should be replaced soon. Don’t throw any weak batteries
away without making sure some measure good with this
test because all batteries could fail if your circuit is wired
incorrectly.
As you’d expect, this circuit is similar to Experiments 21
and 22. From the schematic you can see that we are
using resistors to set the voltages at the bases of the
transistors. The resistor values were selected so that if
the two battery voltages are equal then NPN2’s base will
have a higher voltage and only LED2 will be lit (as in
Experiment 22 when we had a good 1.5V battery). In
fact, LED1 will only be on if your Playground’s battery
voltage is at least 2V higher than that of the battery you
are testing. We do this because we don’t want to reject a
good battery that’s just not as good as our reference
battery. Of course, if our reference battery is weak then
any battery tested will appear good.
Remember to disconnect the battery wire when you’re
not using the circuit to avoid draining the 9V battery.
EXPERIMENT #23: 9 Volt Battery Tester
Wiring Checklist:
o 1-to-3-to-27-to-47
o 26-to-50-to-39-to-45
o 15-to-46-to-48
o 2-to-16
o 4-to-19
o 38-to-17-to-20
o 18-to-42-to-44
Schematic
Now it’s time to introduce another component . . .