A protoboard project that allows a separate 9V (or 9-25V) supply to be used for powering servos driven from a MCU. A controller such as the Arduino can create the driver signals for a servo. The servo requires a 5V supply to operate, but a typical development board, such as a UNO, does not have sufficient overhead in the 5V supply to reliably provide the servo power. It can be done, but is not recommended, especially if the servo is operated under some load. Some servo/motor shields have no provision for a separate power supply, even if they support a separate supply for attached DC or stepper motors. To reliably and safely support servos during project development a unit that can inject a suitable 5V supply into the servo cable is a useful addition to the workbench.
Prototyping
board. Any board of a suitable size can be used. This
one is 70mm x 30mm with holes through the centre section and tabs at each
end. The project uses the tabs for easy connection of the servo
flying leads and pin headers.
Barrel jack (5.5/2.1mm). This size matches the Arduino and is commonly available with 9V adapters.
Servo cables.
3-wire servo leads with solder tail and 3-pin 0.1" female conenctor.
Capacitors. 10uF electrolytic and 0.1uF ceramic in this example. The actual values and types depend a lot on the input source and the expected usage. The 7805 can operate quite happily without additional capacitors.
8-pin male header. Only 6 pins are actually
required for the servos, but the extra two can be used to provide a 5V/Gnd
output.
3D-printed case with screws to suit.
Label for case (see below).
The device will be powered from any supply capable of providing 9-25V DC. The regulator is quoted at up to 2A, but the actual rating will depend on the heatsink and the duty cycle.
An option not considered for this project is to add a USB connection with the 5V supply wired straight through to the output pins. If this upgrade is added then a diode would be required to ensure the USB 5V is not fed back into the 7805 regulator. A switch would achieve a similar result without the voltage drop.
The Circuit layout is quite
simple. The servo signal and ground wires are connected straight
through from the connecting tabs on one end to the header pins at the
other. The servo +5V input is not connected to anything.
The barrel jack is wired with a positive pin to the input of the 7805. The 10uF capacitor is wired across the input to ground. The 7805 ground, the input grounds and the output grounds are all tied together. The 7805 output is wired to the output +5V headers, with a 0.1uF capacitor to ground.
