This is a very standard board design for driving servos. I use several version of it on a number of my robots.
I just connect it with jumper wires. Connect from Raspberry pi 3.3v to VCC (you won't need to connect anything to V+ as it is used for a level shifter when using a 5v MCU) connect GND to ground then of course SDA to SDA and SCL to SCL.
You won't need any power to the servo terminal or any servos attached to talk to the PCA9685 chip. When you attach the 3.3v to VCC and GND the red power light should come on to show you the chip has powered up. After the SDA and SCL wires r connected you should be able to detect the board with i2cdetect -y 1
I wrote a my own very basic driver for this board.
Code: Select all
# Copyright (c) 2017 Out of the BOTS
# http://outofthebots.com.au/
# Author: Shane Gingell
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# Servo class provides very basic functionality for controlling
# sevoing using the PCA9685 chipset with a RPi.
import smbus #import the System Mangement package for I2C coms
import time
class Servo :
global bus
global address
bus = smbus.SMBus(1) #RPi3 uses bus 1 but if using bus 0 then change here
address = 0x40 #factory standard I2C slave address change if needed
@classmethod
def __init__(self): #initizing will turn on all servos and set to poiition 0
bus.write_byte_data(address, 0x01, 0x04)
bus.write_byte_data(address, 0x00, 0x01)
time.sleep(0.005)
oldreg0 = bus.read_byte_data(address, 0x00)
newreg0 = (oldreg0 & 0x7F) | 0x10
bus.write_byte_data(address, 0, newreg0)
prescale = int((25000000/(4096*50))-1)
bus.write_byte_data(address, 0xFE, prescale)
bus.write_byte_data(address, 0, oldreg0)
time.sleep(0.005)
bus.write_byte_data(address, 0, oldreg0 | 0x80)
bus.write_byte_data(address, 0xFA, 0)
bus.write_byte_data(address, 0xFB, 0)
bus.write_byte_data(address, 0xFC, 0x33)
bus.write_byte_data(address, 0xFD, 0x01)
def set_servo (self,servo_number, position): #routine for setting servo positions. no error checking
attemps = 5
for trys in range (attemps):
try:
step = 202//90
if position < -90 : position = -90
if position > 90 : position = 90
if position == 0 : offtime = 307
else : offtime = 307 + (step * position)
startreg = servo_number * 4 + 8
bus.write_byte_data(address, startreg, offtime & 0xff)
bus.write_byte_data(address, startreg+1, offtime >> 8)
return
except:
print"try failed " + str(trys)
print "reached max attemps exiting"
#still much funtionality missing especally a shutdown down function.
and here is a very simple example program to use it
Code: Select all
from Servo import Servo #import servo class
robot = Servo() #create instance of Servo
#set first 8 servos to position 60 degree and set next 8 servos to -60 degrees
robot.set_servo (0, 60)
robot.set_servo (2, 60)
robot.set_servo (3, 60)
robot.set_servo (4, 60)
robot.set_servo (5, 60)
robot.set_servo (6, 60)
robot.set_servo (7, 60)
robot.set_servo (8, -60)
robot.set_servo (9, -60)
robot.set_servo (10, -60)
robot.set_servo (11, -60)
robot.set_servo (12, -60)
robot.set_servo (13, -60)
robot.set_servo (14, -60)
robot.set_servo (15, -60)
# do beaware I haven't created a shutdown toutine so even after the program termintes
# the PCA9685 will continue to hold these positions until power down.
