Powering Servos

The power input section of the HAT and Bonnet are both on the left hand side.

 

The HAT has both 2.1mm DC jack and a terminal block

 

The Bonnet has a spot for either DC jack or terminal block

Powering Servos / PWM

The drivers have two power supplies. One is VCC - that is the 3.3V power from the Raspberry Pi, it is used to power the PWM chip and determines the I2C logic level and the PWM signal logic level. This supply will always be on if the Pi is plugged in and working, check the PWR LED on the Pi (it's the red LED on the Pi 2, 3. Pi Zero does not have a PWR LED, look for a blinking activity LED)

To power servos you will need to also connect the 5-6V V+ power supply - this is the power supply for the servos. (If you are lighting up single 20mA standard draw LEDs you may not need this power supply, but I'm assuming you want to use servos here.) This power supply should be 5 or 6VDC, most servos work well at 5V and if you give them 6V will be a little stronger.

You can connect this power through the terminal block or the 2.1mm DC jack. There is reverse-polarity protection in case you hook up power backwards, however you should use either the DC jack or the terminal block, not BOTH!

Use either a 5V wall adapter, 2 Amp+ is recommended

OR

Or, for portable use, a 4 or 5 x AA battery pack can be connected to the terminal block.

Current Draw Requirements

Nearly all servos are designed to run on about 5 or 6v. Keep in mind that a lot of servos moving at the same time (particularly large powerful ones) will need a lot of current. Even micro servos will draw several hundred mA when moving. Some High-torque servos will draw more than 1A each under load.

Good power choices are:

SERVOS CAN USE A LOT OF POWER! It is not a good idea to use the Raspberry Pi's 5v pin to power your servos! Electrical noise and 'brownouts' from excess current draw could cause your Pi to act erratically, reset and/or overheat. Seriously, keep the Pi power supply and the Servo power supply completely seperate!

Adding a Capacitor to the thru-hole capacitor slot

We have a spot on the PCB for soldering in an electrolytic capacitor. Based on your usage, you may or may not need a capacitor. If you are driving a lot of servos from a power supply that dips a lot when the servos move, n * 100uF where n is the number of servos is a good place to start - eg 470uF or more for 5 servos. Since its so dependent on servo current draw, the torque on each motor, and what power supply, there is no "one magic capacitor value" we can suggest which is why we don't include a capacitor in the kit.

There are slots on both the bonnet and HAT for an optional capacitor. You may not need the capacitor, it's only if you find that you servo power supply is drooping enough to affect functionality

Last updated on 2018-03-20 at 10.40.16 PM Published on 2015-01-02 at 05.28.01 PM