DEV-13042

Page 1 of 9   SparkFun Blocks for Intel® Edison - PWM Introduction SparkFun’s PWM Block for the Intel Edison allows you to add eight channels of I2C controlled PWM output to your Edison stack. The headers are spaced to allow you to directly connect servo motors to the block, and an auxiliary isolated power input on the headers allows for input voltages and currents above what the rest of the Edison can use or provide. PWM Block Suggested Reading If you are unfamiliar with Blocks, take a look at the General Guide to Sparkfun Blocks for Intel Edison. Other tutorials that may help you on your Edison adventure include: • Programming the Edison - This tutorial assumes you are not using the Arduino IDE, so you’ll want to familiarize yourself with C++ development on the Edison. • Powering Your Project • Connector Basics • PWM Basics • LED Basics Board Overview The “top” side of the board is the most interesting, so we’ll look at that first. Page 2 of 9 1. PWM outputs - Each PWM channel has a three-pin, 0.1" spaced header footprint. The output order is appropriate for most servo motors. All you need to do is add male header pins, and you can connect servos directly to the block. The VIN pin is, by default, floating. Before you can drive a servo, you’ll need to provide power to that rail. 2. Auxiliary Power Input - These pads are provided to allow you to connect an external power supply to the PWM channels. This allows you to use a higher voltage, higher current supply (for instance, a 7.2V 2S LiPo cell) to power the devices connected to the PWM outputs without risking damage to the Edison. 3. VSYS->VIN jumper - If you don’t need the extra oomph of an external power supply (because you’re driving small LEDs or a small servo, perhaps), you can bridge this jumper with a solder blob to draw power from the Edison VSYS rail. When running from USB, you can expect that rail to be approximately 4.0V. 4. Address jumpers - These jumpers allow you to set the address the PCA9685 PWM chip on this board will use. Each jumper corresponds to a single address bit; closing a jumper makes that bit a ‘1’. The default address is 0x40. Thus, closing A0 would make the address 0x41, A1 makes it 0x42, A0 and A1 make it 0x43, and so on. The “back” of the board is far more boring, with no jumpers or components to mention. This is the side that the Edison module will mate with, so you will be able to change jumpers without detaching the Edison. Using the PWM Block To use the PWM Block, simply attach an Intel Edison to the back of the board, or add it to your current stack. Blocks can be stacked without hardware, but it leaves the expansion connectors unprotected from mechanical stress. Page 3 of 9 PWM Block Installed We have a nice Hardware Pack available that gives enough hardware to secure three blocks and an Edison. Intel Edison Hardware Pack NOTE: The PWM Block does not have console access or a voltage regulator. It is recommended to use a console communication block in conjunction with this block like ones found in the General Guide to SparkFun Blocks for Intel Edison. C++ Code Examples We’re assuming that you’re using the Eclipse IDE as detailed in our Beyond Arduino tutorial. If you aren’t, you’ll need to read that tutorial to get up to speed. Getting Started Follow the instructions in the programming tutorial to create a new project named “SparkFun_PWM_Edison_Block_Example”. Once you’ve created the project, open the project files on the disk (hint: you can find the path to the project by choosing “Properites” from the project menu), and copy the source files found in the SparkFun PWM Block for Edison C++ Library directly into the “src” directory. D O W N L O A D A ZI P FIL E O F T H E RE P O S I T O R Y Hardware Connection Page 4 of 9 For this example, we’ve got a sub-micro servo motor and a common anode RGB LED connected to the PWM block outputs. We’ve closed the VSYS->VIN jumper with a solder blob, so we’re drawing power from the Edison’s supply. For a larger servo motor or more LEDs, you should open that jumper, and connect an external supply to the VIN and GND pads at the end of the header. Of course, you can connect any other device to the outputs here – the PWM input to a motor driver, a buzzer, what have you. We just want to demonstrate the core capabilities of this block, which is to provide servo driving and visually normalized LED outputs. Code Everything you need to know is in the comments. Page 5 of 9 /************************************************************* ***************   * SparkFun_PWM_Edison_Block_Example.cpp   * Example code showing how to use the SparkFun PWM Edison Blo ck   * Mike Hord @ SparkFun Electronics   * 9 June 2015   * https://github.com/sparkfun/SparkFun_PWM_Block_for_Edison_C PP_Library   *   * This file is a demonstration program showing the various fu nctions that we've   * provided for working with the PCA9685 IC on the SparkFun PW M Edison Block.   * It uses an RGB LED and a small servo motor to show what th e library can do.   *   * Resources:   * Requires Intel's MRAA framework. This can be downloaded fro m either the   * GitHub site (https://github.com/intel­iot­devkit/mraa) or i n pre­built form   * from http://iotdk.intel.com/sdk/mraa­update/.   *   * Development environment specifics:   * Developed in the Intel iot­ide­dk Eclipse on Win 7 (v1.0.0. 201502201135)   * Using lib­mraa v0.6.2   * On Edison poky­linux image build ww18­15   *   * This code is beerware; if you see me (or any other SparkFu n employee) at the   * local, and you've found our code helpful, please buy us a r ound!   * *********************************************************** *****************/  #include "mraa.hpp"  #include "SparkFun_pca9685_Edison.h"  #include   #include   using namespace std;  // These channel definitions mirror the ones used in the PWM B lock hookup guide.  #define SERVO 0  #define RED 2  #define GREEN 3  #define BLUE 4  // Uncomment one or both of these defines to enable the approp riate demo. Do  //  note servo motors and LEDs are best used at different freq uencies and  //  polarities, so hooking both at once will give you bad resu lts.  #define SERVO_DEMO  //#define LED_DEMO  // main() runs once and completes; there's no infinite loop he re. Do note,  //  though, that whatever settings you write to the PWM modul e will persist  Page 6 of 9 //  after the code has completed.  int main()  {    // Variables to be used elsewhere in the program.    uint16_t startTime, stopTime;    mraa::I2c* pwm_i2c;   // We need to create an I2c object tha t we can pass to                          //  the pca9685 constructor. If you ha ve more than one                          //  PCA9685 device on your bus (eithe r by stacking more                          //  than one PWM block or by adding ex ternal boards via                          //  the I2C Expansion Block), you'll n eed to create a                          //  different I2c object for each one!    pwm_i2c = new mraa::I2c(1); // Tell the I2c object which bu s it's on.    pca9685 pwm(pwm_i2c, 0x40); // 0x40 is the default address f or the PCA9685.    // In general usage, you don't need to worry about getting o r setting the    //  mode registers or the prescaler register. I'm including  these lines here    //  just for example completeness purposes.    cout