Elenco Snap Circuits SnapMicro I Deluxe &reg - Manual (Page 61)

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Battery Tester Program;
Modify the voltmeter program in project 15 to be as shown above. This program adds an error message
if the battery voltage being checked gets close to or greater than the voltage level of the micro-controller.
If fresh batteries are installed in the Snap Circuit® battery holder, the battery checker circuit can be used
to check the voltage on any battery up to 4.3 volts.