Re: Larson Scanner with a 9v Battery

#22641
Windell Oskay
Keymaster

The microcontroller on the Larson Scanner is rated for an absolute maximum of 5.5 V. Any more than this can permanently damage it, and potentially create a hazardous situation. Chips have been known to overheat or even explode if exposed to too much voltage.  And, the resistors in the circuit are configured to give a safe level of current at 3 V.

Resistors alone cannot reduce the voltage from the battery in such a way that there is a guaranteed safe voltage level. (This is because as the current drawn goes to zero, so does the voltage across the resistor– effectively, the full 9 V goes across the microcontroller at turn-on time.)
The *safe* way to run the Larson Scanner would be to give it its own 3 V power supply– from a separate pair of AA or AAA batteries, or a CR2032 coin cell if need be. This can be very compact, if that is the issue.
Another method would be to use a set of diodes to drop the voltage. A small signal diode (such as a 1N914) drops about 0.7 V. You could use 8 of them in series to drop the 9 V to about 3.4 V.  Or, you could use three red LEDs, each of which drops about 1.8 V, to drop 5.4 V, giving you about 3.6 V. This would also have the side effect of giving a few more red LEDs for the costume.