Isolating the Logic Section

If the logic section (including the processor) resets because of a sudden drop of supply voltage when the motors are turned on, consider putting a diode between the supply and the input of the linear regulator. The diode acts as a switch so that if the input capacitor of the linear regulator has a higher voltage than the supply, the capacitor does not get drained to ``help'' the motors.

You should always take the diode forward voltage drop into consideration. Schottky Barrier diodes typically have a lower forward voltage drop at about 0.5V (100mA current). Take into consideration of the minimum input voltage of the linear regulator and you'll know the minimum battery voltage.

Instead of only using a .1µF input capacitor, you can consider adding another 2µF capacitor (in parallel) to improve the isolation from the motor voltage.

The following figure shows how to use a diode for logic ``stroke'' protection.

Figure 8.1: Protection from Sudden Drain of Supply Voltage