Addressing the HAT

Each HAT in the stack must be assigned a unique address. This is done with the address jumpers on the middle right of the board. The I2C base address for each board is 0x40. The binary address that you program with the address jumpers is added to the base I2C address.

To program the address offset, use a drop of solder to bridge the corresponding address jumper for each binary ‘1’ in the address.

This photo is from the Arduino Shield version of this driver but its the same setup

Board 0: Address = 0x40 Offset = binary 00000 (no jumpers required)
Board 1: Address = 0x41 Offset = binary 00001 (bridge A0 as in the photo above)
Board 2: Address = 0x42 Offset = binary 00010 (bridge A1)
Board 3: Address = 0x43 Offset = binary 00011 (bridge A0 & A1)
Board 4: Address = 0x44 Offset = binary 00100 (bridge A2)

etc.

Principle of operation

The module is based on the PCA9685 controller, which allows PWM outputs to be controlled using I2C communication and an integrated clock. The module has 6 bridges to select the address of the board and thus allow up to 62 controllers to be placed on the same bus for a total of 992 servomotors (addresses available 0x40 to 0x7F).
It can drive PWM outputs with adjustable frequency and 12-bit resolution. The module is compatible with 5V and 3.3V microcontrollers.

Powering Raspberry Pi / Servos

The drive integrates two power modules. One is the 5V power supply of the MP1584 voltage regulator module, which is used to power the Raspberry Pi, and the 3.3V power supply obtained by the RT9193-33 voltage regulator module is used to supply power to the PWM chip, which determines the I2C logic level and the PWM signal logic level. If the Pi is plugged in, power to the Raspberry Pi is controlled by the HAT’s onboard power switch, check the PWR LED on the Pi (it’s the red LED on the Pi 2, 3, 4. Pi Zero doesn’t have a PWR LED, look for a blinking Activity LED )

Another MP2482EN module supplies power to the steering gear and the onboard 5V pin header, and the power supply connected to the onboard power interface supplies power to both modules at the same time.

Connect to the 2P XH2.54 power socket

Connect to the screw terminals

You can connect this power supply through junction box or 2P XH2.54 DC interface, this power supply should be 6~18VDC. There is reverse polarity protection if you connect the power supply backwards, but you should use either the 2P XH2.54 DC socket or the terminal blocks, not both! (If you’re lighting a single 20mA standard draw LED, you can use the Raspberry Pi USB for power, but I’m assuming you want to use a servo here.)

Powered by USB adapter

Note: If you just connect the Raspberry Pi USB power port, the Raspberry Pi and PCA99685 and the 3.3V pin header will work normally, but the servo power and 5V pins on the HAT will not work. Please do not use the Raspberry Pi USB port and the HAT power port for power supply at the same time!

Current Draw Requirements

Connecting a Servo

Most servos come with a standard 3-pin female connector that will plug directly into the headers on the Servo HAT headers. Be sure to align the plug with the ground wire (usually black or brown) with the bottom row and the signal wire (usually yellow or white) on the top.

Works with any servo that can be powered by 5V and take 3.3V logic level signals.

Adding More Servos

Up to 16 servos can be attached to one board. If you need to control more than 16 servos, additional boards can be stacked as described on the next page.

Dimming LEDs

This HAT use the PCA9685. Each channel of the HAT can be used to control the brightness of an LED.  The PCA9685 generates a high-speed PWM signal which turns the LED on and off very quickly.  If the LED is turned on longer than turned off it will appear brighter to your eyes.

First you’ll need to import the necessary modules, initialize the I2C bus for your board, and create an instance of the class.

The PCA9685 class provides control of the PWM frequency and each channel’s duty cycle.  Check out the PCA9685 class documentation for more details.

For dimming LEDs you typically don’t need to use a fast PWM signal frequency and can set the board’s PWM frequency to 60hz by setting the frequency attribute:

The HAT support 16 separate channels that share a frequency but can have independent duty cycles. That way you could dim 16 LEDs separately!

The PCA9685 object has a channels attribute which has an object for each channel that can control the duty cycle. To get the individual channel use the [] to index into channels.

Now control the LED brightness by controlling the duty cycle of the channel connected to the LED. The duty cycle value should be a 16-bit value, i.e. 0 to 0xffff (65535), which represents what percent of the time the signal is on vs. off.  A value of 0xffff is 100% brightness, 0 is 0% brightness, and in-between values go from 0% to 100% brightness.

For example set the LED completely on with a duty_cycle of 0xffff:

After running the command above you should see the LED light up at full brightness!

Now turn the LED off with a duty_cycle of 0:

Try an in-between value like 1000:

You should see the LED dimly lit.  Try experimenting with other duty cycle values to see how the LED changes brightness!

For example make the LED glow on and off by setting duty_cycle in a loop:

These for loops take a while because 16-bits is a lot of numbers. CTRL-C to stop the loop from running and return to the REPL.

That’s all there is to dimming LEDs using CircuitPython and the PWM HAT!

Controlling Servos

We’ve written a handy CircuitPython library for the various PWM/Servo kits called Adafruit CircuitPython ServoKit that handles all the complicated setup for you. All you need to do is import the appropriate class from the library, and then all the features of that class are available for use. We’re going to show you how to import the ServoKit class and use it to control servo motors with the OSOYOO PWM HAT.

First you’ll need to import and initialize the ServoKit class. You must specify the number of channels available on your board. The HAT have 16 channels, so when you create the class object, you will specify 16.

Now you’re ready to control both standard and continuous rotation servos.

Standard Servos

To control a standard servo, you need to specify the channel the servo is connected to. You can then control movement by setting angle to the number of degrees.

For example to move the servo connected to channel 0 to 180 degrees:

To return the servo to 0 degrees:

With a standard servo, you specify the position as an angle. The angle will always be between 0 and the actuation range. The default is 180 degrees but your servo may have a smaller sweep. You can change the total angle by setting actuation_range.

For example, to set the actuation range to 160 degrees:

Often the range an individual servo recognises varies a bit from other servos. If the servo didn’t sweep the full expected range, then try adjusting the minimum and maximum pulse widths using set_pulse_width_range(min_pulse, max_pulse).

To set the pulse width range to a minimum of 1000 and a maximum of 2000:

That’s all there is to controlling standard servos with the PWM HAT, Python and ServoKit!

Continuous Rotation Servos

To control a continuous rotation servo, you must specify the channel the servo is on. Then you can control movement using throttle.

For example, to start the continuous rotation servo connected to channel 1 to full throttle forwards:

To start the continuous rotation servo connected to channel 1 to full reverse throttle:

To set half throttle, use a decimal:

And, to stop continuous rotation servo movement set throttle to 0:

That’s all there is to controlling continuous rotation servos with the PWM HAT, Python and ServoKit!

# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT

"""Simple test for a standard servo on channel 0 and a continuous rotation servo on channel 1."""
import time
from adafruit_servokit import ServoKit

# Set channels to the number of servo channels on your kit.
# 8 for FeatherWing, 16 for Shield/HAT/Bonnet.
kit = ServoKit(channels=8)

kit.servo[0].angle = 180
kit.continuous_servo[1].throttle = 1
time.sleep(1)
kit.continuous_servo[1].throttle = -1
time.sleep(1)
kit.servo[0].angle = 0
kit.continuous_servo[1].throttle = 0