This HAT has 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)
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 blue 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!
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:
- 5v 2A switching power supply (up to perhaps 4 servos)
- 5v 4A switching power supplies (up to perhaps 8 servos)
- 5v 10A switching power supply (up to perhaps 16 servos)
- 4xAA Battery Holder - 6v with Alkaline cells. 4.8v with NiMH rechargeable cells, portable!
- 4.8 or 6v Rechargeable RC battery packs from a hobby store.
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.