MTE380 DC and Stepper Motor Controller with Analog Inputs.

Transcription

1 MTE380 DC and Stepper Motor Controller with Analog Inputs. Design by: Vecheslav Silagadze, If you find any bugs in the code or design please let me know.

2 Table of Contents TABLE OF CONTENTS... 2 SOFTWARE SETUP:... 3 HARDWARE SETUP:... 4 DEVICE DESCRIPTION:... 6 MOTORS:... 6 SENSORS:... 6 LOADING CODE:... 7 CONTROL DESCRIPTION:... 8 DC MOTORS:... 8 STEPPER MOTORS:... 9 SENSORS: SUMMARY TABLE: TROUBLESHOOTING:... 11

3 Software Setup: You will require three pieces of software in order to develop code and load it into the device. The first is the MPLAB IDE from Microchip Technologies. You will need to go to then download and install MPLAB. The second piece of software you will need is the C30 compiler from Microchip in order to be able to program the device in C (as opposed to assembly language.) The C30 compiler can also be found at the Microchip website mentioned above. When installing the C30 compiler you will be asked if you want the setup to modify you PATH variable to include. It is extremely important that you choose yes, otherwise you will have to do it manually. Finally you will need the WinPic programming software in order to load code into the device. You can download this software at Or simply search for winpicpr.zip on Google. Once you have installed all of the above pieces of software you will need to setup the MTE380 project in MPLAB. Download and unzip the MTE380 code template into some directory. Open MPLAB and from the top menu select project -> open. Then select mte380.mcp in the directory in which you unzipped the code. The most important thing to verify is that the linker script and library files have been loaded correctly. You can do this by looking at the project layout in the right hand window, and making sure that under Library Files you have libp30f2010.a and it does not state file not found beside it. Similarly, make sure you have p30f2010.gld under Linker Scripts. If one of these is missing you will need to add it by right clicking on the project layout section of the file you want to add and selecting Add files. Then go to the directory in which the C30 compiler is installed and find the file with the above name. The libp30f2010.a file is probably in C:\Program Files\Microchip\MPLAB C30\lib, and the p30f2010.gld file is probably in C:\Program Files\Microchip\MPLAB C30\support\gld Once you have completed all of the above you can try and build the project by selecting project -> build all in the MPLAB top menu. If you see BUILD SUCCEEDED in the output window, that means everything is setup correctly and you are ready to code. Note: MPLAB is a fairly primitive IDE. If you are used to working with more sophisticated development studios, like Visual Studio or Eclipse, it will take some getting used to.

4 Hardware Setup: Below is the circuit diagram of the device you are working with. Figure 1: Circuit diagram This is the logical layout of the system. In other words, it is used to describe how the circuit functions in a manner that is easily readable. Notice that each component in the circuit above has a name beside it. For instance, the big block in the center is called MCU. The two blocks to the right are called STEP and DC. These are the microcontroller, the stepper motor driver and the DC motor driver, respectively. The names of these things on the circuit can be cross referenced with the circuit layout (i.e. the PCB design) so that you know which part goes where and how they are interconnected. Below is the circuit layout with some parts omitted for clarity.

5 Figure 2: Device layout Notice that in the center you can see the part labeled MCU and to the right you can see the parts labeled STEP and DC (bottom right.) Also notice that all of the resistors and capacitors are labeled (R1, R2, etc.) along with their values. Again, you can cross reference this with the circuit diagram above so that you know how to solder these parts onto the PCB. When soldering the components (especially the chips) it is important to be as quick as possible with each pin. If you apply heat to the chip pins for too long you risk damaging it. A rule of thumb is that you should not apply heat to the pin for more than 2 seconds. If you think the chip is overheating, wait for it to cool before going on to the next pin. Note: Be sure to put a capacitor across the DC motor terminal! Or else you will experience random resets every time you run the motor at load. Grounding the motor chassis is a good idea too. Note: The order of wires for the stepper motor connector should be: brown, orange, black, yellow, red. Referenced from top to bottom on the PCB stepper motor connectors.

6 Device Description: The device is designed to be able to control two stepper motors, two DC motors and to be able to read analog inputs from sensors. The brain of the device is a dspic30f2010 microcontroller (labeled MCU.) The microcontroller is basically a complete system on a chip. It includes a microprocessor core, as well as RAM, and peripheral modules like a serial (UART) port and an analog to digital converter. The purpose of the microcontroller in this case is to run code in order to control motors and read in sensor information. Motors: The microcontroller is not designed to supply significant amounts of current (20 milliamps at most) so in order to run a DC motor, which requires as much as 500 milliamps of current, there must be a driver. The driver is basically an amplifier. It takes a small signal from the microcontroller (5V at a few microamps) and amplifies it to a large signal (12V at 500 milliamps) that goes into the motor. Similarly the stepper motor requires its own driver. However, because the stepper motor is not quite as simple to run as a DC motor, it requires 4 wires (for the particular model you will be using) and uses a different driver. Looking at the circuit you can see there is a chip called DC, and another called STEP. Of course, these are the DC motor driver and stepper motor driver, respectively. The DC motor driver is the L298 chip. You can look up the datasheet for it online if you are interested in the details of its operation. The stepper motor driver is the ULN2803A. This is basically 8 power transistors packaged on a chip. The connectors for the stepper motors and DC motors are labeled STEPPER1, STEPPER2, DC1, and DC2. The stepper motor connector should be setup such that the wires are in the following order from the top of the PCB: brown, orange, black, yellow, red. If you do it any other way it will not work. Sensors: The microcontroller can connect up to 5 analog sensors. The sensor inputs are labeled A0 through A4 on the board towards the top right. You will notice an area on the top of the board with lots of holes and copper around them. This is the prototype space. You can put in any resistors, capacitors, or whatever else you need in order to convert the sensor output into a voltage the microcontroller can read. So for example if you have a switch you would need to wire it up as shown below: Figure 3: Switch to analog port circuit

7 The wire labeled OUT would go to one of A0 through A4. Note that the top line of holes in the prototype area is tied to 5V, and the bottom line (except A0 A4) is tied to ground. This setup is so that you can easily wire power to your sensors. Loading Code: Loading code on the device is fairly straightforward. Once you select project -> build all in MPLAB, the program will generate a hex file (machine language code) called mte380.hex. In order to load this code you need to open the WinPic software. In the top menu go to device -> select, and pick the dspic30f2010 from the dropdown menu. Now go to file -> load and select the file mte380.hex from the directory in which you unzipped the code. Go to the Device Config tab and ensure that FWDTEN is set to disabled (for some reason WinPic doesn t seem to recognize that setting correctly from the hex file.) Now connect the device with a straight through serial cable to your computer and then turn on the power (i.e. plug in the power adapter.) Now select device -> program from the top menu in WinPic and the code will be programmed onto the chip. Note: After programming be sure to disconnect the serial cable! This is important because while the cable is connected the device could be in programming mode and may not run. In general do not leave the serial cable plugged in for any length of time.

8 Control Description: There are only 6 functions that you need to understand in order to use the device. Everything else is taken care of for you in the background. These functions allow you to set the position and speed of the stepper motor, and they allow you to set the power delivered to the DC motors. DC Motors: The mode of DC motor control used by the device is called pulse width modulation (PWM.) The idea behind this is fairly simple. You send a pulse train to the motor terminals, and control the average amount of power delivered by varying the ratio of the amount of time the power is on to the amount of time the power is off. The figure below illustrates this concept. Figure 4: PWM illustration The question arises: why control a DC motor in this way? Why not just supply a set voltage equal to the average we are looking for? Certainly this would be easier in many ways, and it would avoid a significant amount of power losses associated with constantly switching the power on and off. There are a number of reasons the PWM method is used. One of the main ones is that it allows a simple digital system to control a fundamentally analog system like a DC motor. All one needs is a couple of simple transistor switches, as opposed to a complicated variable voltage regulator. The API has one simple function for setting the power output to each motor. These are set_dc1_power(int power), and set_dc2_power(int power). The input variable is the power, and ranges from -100 to 100 with the sign representing direction. So calling with the function with 30 will result in 30% of maximum power in the positive direction. Similarly, calling the function with -70 will result in 70% of maximum power in the negative direction. Note: If you just want a quick table summary of all functions, look at the end of this section.

9 Stepper Motors: Stepper motor control is a bit more complicated than DC motor control. Basically the stepper motor is a cheap alternative to a servo motor. A servo motor is basically just a DC motor with some electronics attached that allow you to control the position of the motor. A stepper motor tries to emulate this through its construction it has a series of permanent magnets and coils. By energizing certain coils (i.e. magnetizing them) the motor will align the coils with the permanent magnets. By energizing the coils in a specific order, the motor can be made to rotate in a set direction in a series of steps. The specific motor used in this course is 2-2 phase unipolar. It has four wires that need to be driven in the following order in order to make the motor rotate. Time Coil A+ 12V 12V 0V 0V 12V 12V 0V 0V 12V 12V Coil A- 0V 0V 12V 12V 0V 0V 12V 12V 0V 0V Coil B+ 12V 0V 0V 12V 12V 0V 0V 12V 12V 0V Coil B- 0V 12V 12V 0V 0V 12V 12V 0V 0V 12V Figure 5: Stepper motor control sequence To make the motor rotate in the opposite direction, the pattern simply needs to be run backwards. Because the stepper motor has the facility to control its position in this way there are actually two modes in which the stepper motor can be controlled. The first is position mode and the second is speed mode. In position mode, you simply set the desired position of the motor and the motor will rotate to that position. In speed control mode you simply set a rotation speed you desire in rotations per minute (RPM) and the motor will continuously rotate at that speed. There are two functions for the control of the stepper motor, one for each mode of control. For speed control mode the functions are set_stepper1_speed( int rpm ), and set_stepper2_speed( int rpm ). A positive number will result in rotation in one direction, while a negative number will result in rotation in the opposite direction. If you wish to control the position of the motor, the two function are set_stepper1_position(unsigned int position) and set_stepper2_position(unsigned int position). The input to the two functions is the desired position in hundredths of a degree. So if you wish the motor to move to position 127 degrees, you must call the function with Note: Position resolution of the stepper motor you are using is 7.5 degrees. So you cannot control the motor with any greater precision. This means if the motor is at degrees, you CANNOT move it to something like 191 degrees. The nearest positions are 180 degrees and 195 degrees. Note: The controller will automatically choose the fastest way to reach desired position. So if the motor is at degrees and you want it to move to 0 degrees, it will automatically rotate in the positive direction. Whereas if you tell it to move to 345 degrees, it will automatically move in the negative direction.

10 Sensors: Access to the sensors is extremely easy. Simply read values from the global variable array sensor[0] through sensor[5], corresponding to analog inputs 0 through 4 (A0 through A4 on the PCB). The values are updated automatically in real time at around 5KHz. The value ranges from 0 to 1024 and corresponds to a linearly scaled input value of 0V to 5V. So for example if the input voltage is 1.5V, then the sensor reading will be (1.5/5)*1024 = 307. The conversion formula is: Digital Value = (Vin/5V)*1024 Summary Table: Category Function DC set_dc1_power(int power) Motors Stepper Motors set_dc2_power(int power) Description Set percentage power input to DC motor 1. Sign controls direction. Set percentage power input to DC motor 2. Sign controls direction. set_stepper1_position(unsigned int position) Set position setpoint for stepper motor 1. set_stepper2_position(unsigned int position) Set position setpoint for stepper motor 2. set_stepper1_speed(int rpm) set_stepper1_speed(int rpm) Set rotation speed for stepper motor 1. Sign controls direction. Set rotation speed for stepper motor 2. Sign controls direction. Sensors unsigned int sensor[n] Analog input reading. Scaled from 0V to 5V to 0 to Figure 6: Function summary table

11 Troubleshooting: Below are some quick hints for problems you may run into in constructing and running your circuit. In general here is the series of steps you should use in verifying that your circuit works once you have constructed it: 1. The first step is to make sure your circuit passes the smoke test. If you turn it on and there is smoke, it means you failed the test. 2. Next, check the power. The LED should turn on once power is applied. If this is not the case then either you soldered your LED backwards, or the voltage regulator isn t working, or there is a short circuit somewhere (which generally means you will see smoke very soon.) 3. If the power seems to be present, the next step is to try and load the code into the chip. Follow the instructions in the Loading Code section above. 4. If you actually managed to load code into the chip, you re doing pretty good. The next step is to check the oscillator. Turn on the power and use an oscilloscope to probe the oscillator pins on the microcontroller (pins 9 and 10, count from the pin marked with an indent beside it.) You should see a sine-like wave at exactly 6.5MHz. 5. If all of the above check out then your microcontroller is running code and you re all set to start playing with the motors and sensors. Here are some hints if your device fails one of the steps above: 1 If you see smoke, you probably burned one or more components. Before proceeding, replace the component that was smoking and any components that got hot to the touch. Check for any excess solder and fused contacts. Clean up any solder flux with some alcohol (no you can t use beer!!) Other than that just be careful with your soldering. Failed smoke test generally means you were sloppy. Also, check that the dspic chip is not plugged in backwards. If it is, you are pretty much guaranteed to have burned it. Get another one. 2 If there is no power, check that the regulator is soldered in fully. Check the power cables. Generally no power means bad interconnections. 3 If you cannot load code into the chip, it could mean bad soldering as with all of the above. Alternatively it would mean you somehow burned your dspic chip. Try probing the serial port pins while programming and make sure you see a pulse train. If you don t then it usually means there is a bad contact somewhere. Also, some serial ports don t operate on RS-232 levels (+-11V) but only on TTL levels, which means you need to get yourself a decent computer with an RS-232 compliant serial port. 4 This is the most tricky part to fix. It could be bad soldering, some excess solder flux, or damaged capacitors. If the oscillator isn t starting try replacing the capacitors tied to it. Also, make sure you didn t change the configuration settings in the main.c file. The oscillator should be set to PLL x16 mode. As a LAST resort you may contact me, Vecheslav Silagadze for help with your circuit. My is vsilagad@uwaterloo.ca.