Driving servo motors with the Arduino Servo library is pretty easy, but
each one consumes a precious pin - not to mention some Arduino
processing power. The Adafruit 16-Channel 12-bit PWM/Servo Driver Shield will
drive up to 16 servos over I2C with only 2 pins. The on-board PWM
controller will drive all 16 channels simultaneously with no additional
Arduino processing overhead. What's more, you can stack up to 62 of them to control up to 992 servos - all with the same 2 pins!
The Adafruit PWM/Servo Driver is the perfect solution for any project that requires a lot of servos!
This section assumes you do not want to stack the shield with stacking headers. If you want to stack another shield on top, skip to the Stacking Shields section!
The shield plugs in directly into any
shield-compatible Arduino such as Duemilanove, Diecimila, UNO, Leonardo,
Mega R3+, ADK R3+. The only pins required to run are the Ground
I2C control pins.
For backwards compatibility with old Ardunos, SCL
is connected to A5
and SDA is connected to A4
UNOs already have this connection on board. If you are using a Leonardo
or Mega and want to use the A4/A5 pins, cut the traces on the top of
the board between A4 and A5 and the two pins next to them labeled
If you are using a Mega or ADK R2 or earlier, you will have to solder a wire from SCL
Connecting other I2C devices
Since I2C is a 'shared bus' you can still connect other I2C devices to the SDA/SCL pins as long as they do not have a conflicting address. The default address for the shield is address 0x40
Powering Servos / PWM
This shield has two
supplies. One is VCC - that is the 5V power from the Arduino, it is used
to power the PWM chip and determines the I2C logic level and the PWM
signal logic level. When this power supply is working you will see a red
LED. The red LED must be lit for the Arduino & shield to work!
Plug in the Arduino to USB or a wall adapter to provide it.To power servos you will need to also connect the V+ power supply -
this is the power supply for the servos. (If you are lighting up single
LEDs you may not need this power supply.) This power supply should be 5
or 6VDC. You can connect this power through the blue terminal block.
There is reverse-polarity protection in case you hook up power
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
Good power choices are:
SERVOS CAN USE A LOT OF POWER! It is not a good idea to use the Arduino 5v pin to power your servos. Electrical noise and 'brownouts' from excess current draw can cause your Arduino to act erratically, reset and/or overheat.
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
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.
Connecting a Servo
Most servos come with a standard 3-pin female
connector that will plug directly into the headers on the Servo Driver.
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.
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.
If you want to plug shields on top of this one, make sure you pick up a set of shield-stacking headers http://www.adafruit.com/product/85
and solder them instead of the male header
Since this shield only uses the I2C pins
and the I2C bus is sharable, you can stack multiple shields on top of
each other. You will need to have installed stacking headers & right
angle 3x4 connections for it to physically connect. Multiple shields (up to 62!) can be stacked to control still more servos.
Addressing the Shields
Each board in the chain must be assigned a
unique address. This is done with the address jumpers on the upper
right edge 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.
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)
Since the PWM Servo Driver is controlled over I2C, its super easy to use with any microcontroller or microcomputer. In this demo we'll show using it with the Arduino IDE but the C++ code can be ported easily
Download the library from Github
Start by downloading the library from the GitHub repository You can do that by visiting the github repo and manually downloading or, easier, just click this button to download the zip
Rename the uncompressed folder Adafruit_PWMServoDriver and check that the Adafruit_PWMServoDriver folder contains Adafruit_PWMServoDriver.cpp and Adafruit_PWMServoDriver.h
Place the Adafruit_PWMServoDriver library folder your arduinosketchfolder/libraries/ folder.
You may need to create the libraries subfolder if its your first library. Restart the IDE.
We also have a great tutorial on Arduino library installation at:
Test with the Example Code:
First make sure all copies of the Arduino IDE are closed.
Next open the Arduino IDE and select File->Examples->Adafruit_PWMServoDriver->Servo. This will open the example file in an IDE window.
If using a Breakout:
Connect the driver board and servo as shown on the previous page. Don't forget to provide power to both Vin (3-5V logic level) and V+ (5V servo power). Check the green LED is lit!
If using a Shield:
Plug the shield into your Arduino. Don't forget you will also have to provide 5V to the V+ terminal block. Both red and green LEDs must be lit.
If using a FeatherWing:
Plug the FeatherWing into your Feather. Don't forget you will also have to provide 5V to the V+ terminal block. Check the green LED is lit!
Connect a Servo
A single servo should be plugged into the PWM #0 port, the first port. You should see the servo sweep back and forth over approximately 180 degrees.
Calibrating your Servos
Servo pulse timing varies between different brands and models. Since it is an analog control circuit, there is often some variation between samples of the same brand and model. For precise position control, you will want to calibrate the minumum and maximum pulse-widths in your code to match known positions of the servo.Find the MInimum:
Using the example code, edit SERVOMIN until the low-point of the sweep reaches the minimum range of travel. It is best to approach this gradually and stop before the physical limit of travel is reached.Find the Maximum:
Again using the example code, edit SERVOMAX until the high-point of the sweep reaches the maximum range of travel. Again, is best to approach this gradually and stop before the physical limit of travel is reached.
Use caution when adjusting SERVOMIN and SERVOMAX. Hitting the physical limits of travel can strip the gears and permanently damage your servo.
Converting from Degrees to Pulse Length
The Arduino "map()" function
is an easy way to convert between degrees of rotation and your calibrated SERVOMIN and SERVOMAX pulse lengths. Assuming a typical servo with 180 degrees of rotation; once you have calibrated SERVOMIN to the 0-degree position and SERVOMAX to the 180 degree position, you can convert any angle between 0 and 180 degrees to the corresponding pulse length with the following line of code:
pulselength = map(degrees, 0, 180, SERVOMIN, SERVOMAX);
pulselength = map(degrees, 0, 180, SERVOMIN, SERVOMAX);
This function can be used to adjust the PWM frequency, which determines how many full 'pulses' per second are generated by the IC. Stated differently, the frequency determines how 'long' each pulse is in duration from start to finish, taking into account both the high and low segments of the pulse.
Frequency is important in PWM, since setting the frequency too high with a very small duty cycle can cause problems, since the 'rise time' of the signal (the time it takes to go from 0V to VCC) may be longer than the time the signal is active, and the PWM output will appear smoothed out and may not even reach VCC, potentially causing a number of problems.
freq: A number representing the frequency in Hz, between 40 and 1000
The following code will set the PWM frequency to the maximum value of 1000Hz:
setPWM(channel, on, off)
This function sets the start (on) and end (off) of the high segment of the PWM pulse on a specific channel. You specify the 'tick' value between 0..4095 when the signal will turn on, and when it will turn of. Channel indicates which of the 16 PWM outputs should be updated with the new values.
channel: The channel that should be updated with the new values (0..15)
on: The tick (between 0..4095) when the signal should transition from low to high
off:the tick (between 0..4095) when the signal should transition from high to low
The following example will cause channel 15 to start low, go high around 25% into the pulse (tick 1024 out of 4096), transition back to low 75% into the pulse (tick 3072), and remain low for the last 25% of the pulse:
pwm.setPWM(15, 1024, 3072)
pwm.setPWM(15, 1024, 3072)
Can this board be used for LEDs or just servos?
It can be used for LEDs as well as any other PWM-able device!
I am having strange problems when combining this shield with the Adafruit LED Matrix/7Seg Backpacks
We are not sure why this occurs but there is an address collision even
though the address are different! Set the backpacks to address 0x71 or
anything other than the default 0x70 to make the issue go away.
With LEDs, how come I cant get the LEDs to turn completely off?
If you want to turn the LEDs totally off use setPWM(pin, 4096, 0); not setPWM(pin, 4095, 0);
I can't get this to work with my 7-segment LED display.
The PCA9865 chip has an "All Call" address of 0x70. This is in addition to the configured address. This will cause an address collision if used with any other chip addressed to 0x70.