Choosing a Power Source

PICmicro microcontrollers require power supply voltages between 2V and 6V, depending on which PICmicro you are using. Both batteries and mains power supply units provide suitable voltages.

This depends mainly on what the output device you use in the circuit. A few LED's or a 7-segment display draw currents of less than 100mA. On the other hand, a motor or a solenoid may require a few amps to operate. Very few batteries are capable of delivering currents greater than one amp. Even then, battery life will be drastically shortened by such a current demand. Mains power supply units can provide sufficient current, though not the 'battery eliminator' type.

For portable equipment, size and weight could be important considerations when choosing the power source. Provided the current demand is low, batteries are probably the best choice here.

Mains power supply units have a high initial (purchase) cost, but low running costs. Batteries are a very expensive way to buy electricity!

A crucial question, which may leave battery power as the only option!

The mains electricity supply is potentially dangerous. Depending on who is going to use the control system, and where it is going to be used, batteries may be the best option.