The OSOYOO PWM HAT can control 16 PWM outputs via I2C communication, The two on-board voltage regulator modules provide two separate 5V power supplies for the Raspberry Pi and the servo, respectively.Among other things, it allows you to free up inputs and outputs of your microcontroller and drive up to 16 LEDs or servos (or any other module taking a PWM signal as input) using two pins (SCL and SDA) while keeping the pins of your microcontroller for other modules such as sensors. The Raspberry Pi is a microcontroller with integrated Bluetooth and Wifi modules. Very easy to use, it is lightweight and has a higher memory and computing capacity than the Arduino.

In this tutorial we will see how to use Raspberry Pi and OSOYOO PWM HAT to adjust LED brightness and drive servos.

Note: This tutorial assumes that users are familiar with the Raspberry Pi and have a general knowledge base of Python. If you have unfamiliar with these items, as a starting point, we suggest setting up your Raspberry Pi, familiarizing yourself with the graphics user interface (GUI), and then learning the basics of Python. Below are resources to get you started:

RPi Connection

Assembling the OSOYOO PWM HAT with a Raspberry Pi is pretty straight forward. First make sure that nothing is powered. Then, just stack the board onto the Raspberry Pi so that the PCBs line up on top of each other; the HAT is NOT meant to protrude out to the side.

Never plug in a servo while your Raspberry Pi is running. The sudden current spike needed to power your servo will reset your Raspberry Pi. Always plug in all of your servos first, and then boot up.

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)


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

Almost all servos are designed to run on around 5 or 6v. Keep in mind that many servos moving simultaneously (especially large and powerful ones) will require a lot of current. Even tiny servos draw hundreds of milliamps while moving. Some high torque servos can draw over 1A under load.

Here we will use two 18650 batteries to power them. Of course, you can also choose other battery combinations over 6V, or directly use a 6-18V DC power adapter to provide power through the terminals.


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.

Install and test PWM HAT with LEDs

Step 1 – Plug in HAT

Begin by having the Pi shutdown and not powered, plug the HAT on top to match the 2×20 headers, and power up the Pi.

Step 2. Configure your Pi to use I2C devices

To learn more about how to setup I2C with Raspbian, please take a minor diversion to this tutoria.

When you are ready to continue, enter the following commands to add SMBus support (which includes I2C) to Python:

sudo apt-get install python-smbus
sudo apt-get install i2c-tools

i2c-tools isn’t strictly required, but it’s a useful package since you can use it to scan for any I2C or SMBus devices connected to your board. If you know something is connected, but you don’t know it’s 7-bit I2C address, this library has a great little tool to help you find it. python-smbus is required, it adds the I2C support for python!

Don’t forget you must add kernel support for I2C by following this tutorial!

You can then detect if the HAT is found on the #1 I2C port with:\

sudo i2cdetect -y 1

This will search  /dev/i2c-1 for all address, and if an Adafruit PWM/Servo HAT is properly connected and it’s set to its default address — meaning none of the 6 address solder jumpers at the top of the board have been soldered shut — it should show up at 0x40 (binary 1000000) as follows:


Once both of these packages have been installed, and i2cdetect finds the 0x40 I2C address, you have everything you need to get started accessing I2C and SMBus devices in Python.

It’s easy to control PWM or servos with the OSOYOO PWM HAT. There are multiple CircuitPython libraries available to work with the different features of these boards including Adafruit CircuitPython PCA9685, and Adafruit CircuitPython ServoKit. These libraries make it easy to write Python code to control PWM and servo motors.

Python Wiring

First assemble the HAT exactly as shown in the previous pages. There’s no wiring needed to connect the HAT  to the Pi. The example below shows the HAT attached to a Pi.

To dim an LED, wire it to the board as follows. Note: you don’t need to use a resistor to limit current through the LED as the HAT will limit the current to around 10mA.

  • Connect LED cathode / shorter leg to HAT channel GND / ground.
  • Connect LED anode / longer leg to HAT channel PWM.

External power is not necessary to PWM an LED.

To control a servo, wire it to the board as shown in the previous pages, including a barrel jack to the power terminal to attach an appropriate external power source to the HAT. The HAT will not power servos without an external power source!

Python Installation of ServoKit Library

You’ll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!

Once that’s done, from your command line run the following command:

  • sudo pip3 install adafruit-circuitpython-servokit

If your default Python is version 3 you may need to run ‘pip’ instead. Just make sure you aren’t trying to use CircuitPython on Python 2.x, it isn’t supported!

Python Usage

To demonstrate the usage, we’ll use Python code to control PWM to dim an LED and to control servo motors from the Python REPL.

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.

import board
import busio
import adafruit_pca9685
i2c = busio.I2C(board.SCL, board.SDA)
hat = adafruit_pca9685.PCA9685(i2c)

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:

hat.frequency = 60

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.

led_channel = hat.channels[0]

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:

led_channel.duty_cycle = 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:

led_channel.duty_cycle = 0

Try an in-between value like 1000:

led_channel.duty_cycle = 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:

# Increase brightness:
for i in range(0xffff):
    led_channel.duty_cycle = i

# Decrease brightness:
for i in range(0xffff, 0, -1):
    led_channel.duty_cycle = i

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.

from adafruit_servokit import ServoKit
kit = ServoKit(channels=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:

kit.servo[0].angle = 180

To return the servo to 0 degrees:

kit.servo[0].angle = 0

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:

kit.servo[0].actuation_range = 160

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:

kit.servo[0].set_pulse_width_range(1000, 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:

kit.continuous_servo[1].throttle = 1

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

kit.continuous_servo[1].throttle = -1

To set half throttle, use a decimal:

kit.continuous_servo[1].throttle = 0.5

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

kit.continuous_servo[1].throttle = 0

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

Full Example Code

# 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
kit.continuous_servo[1].throttle = -1
kit.servo[0].angle = 0
kit.continuous_servo[1].throttle = 0

Click below link for Library Reference


Related Projects

Introduction of OSOYOO PWM HAT

Getting start with the OSOYOO PWM HAT


Schematics of OSOYOO PWM HAT




Can we use it with Arduino?

Absolutly! We can use the OSOYOO PWM HAT with mutiple micro control boards including Arduino. The only condition is that the main control chip supports I2C communication, which means enabling the communication between the chip and PCA9685 Servo Driver, so as to control multiple servos simultaneously.

Why do two I2C device addresses appear when scanning an I2C address?

The control chip used corresponds to PCA9685. When powered on, there are two I2C addresses, one is the address configured according to the onboard resistance, the default is 0X40, and the other is 0X70, which is configured by the ALLCALLADR register. You can run the demo again to check the value of the register.

Can two identical PWM HATs be stacked?

It can be stacked, but the resistance of the I2C address needs to be changed. In the I2C Address on the left, solder the default upper resistance to the bottom with a soldering iron. Different combinations generate different I2C address combinations, and there are a total of 62 combinations of 2 to the 5th power.

Can this HAT be used for LEDs or just servos?

It can be used for LEDs as well as any other PWM-able device! Use the Signal and Ground pins if you dont mind the LEDs powered by 3.3V and 220ohm series resistor. Or V+ and your own resistor & LED, if you want up to 5V power for the LEDs

If I’m using it with LEDs I cant quite get the PWM to be totally off?

If you want to turn the LEDs totally off use setPWM(pin, 4096, 0); not setPWM(pin, 4095, 0);

No Available Devices

Double check your connections. On a Raspberry Pi, you may get this is indicated with an OSError: [Errno 121] Remote I/O error readout.

On a Raspberry Pi, also make sure that the I2C hardware is enabled. This is usually indicated with an Error: Failed to connect to I2C bus 1. readout.

Checking Your I2C Connection
A simple method to check if your Raspberry Pi can communicate with the PWM HAT over I2C is to ping the I2C bus. On the latest releases of Raspbian Stretch, the i2ctools package should come pre-installed. If it isn’t run the following command in the terminal:

sudo apt-get install i2ctools
Once the i2ctools package is installed, you can ping the I2C bus with the following command in the terminal:

i2cdetect -y 1
You should see a table printed out in the terminal. If the PWM HAT is connected/working properly you should see the address space for 0x40 marked with 40.

Current Draw Issues

Since the Raspberry Pi provides 5V to the module by default, if the control servo power is too large (such as MG996R, DS3120MG), the 5V of the Raspberry Pi will be pulled down. If your servos are drawing more current that your power supply can handle, your Pi Servo pHAT will not operate correctly and the Raspberry Pi may reboot/brown out intermittently.

Can the angle of rotation be precisely controlled?

No, this is just entry-level.

Why does it shake?

It is normal for it to shake slightly. Since the actual angle of the servo is smaller than the minimum physical angle, there will be a current to maintain its angle, which will cause shaking.