Getting Started with the AutoDriver

Contributors: SFUptownMaker

Arduino Library - Configuration

To make your life a little easier, we've developed a fairly comprehensive library for configuring and controlling the AutoDriver. On this page, we'll go through the various commands in the library and the impact they have on the operation of the AutoDriver board.

As mentioned earlier, the AutoDriver requires more configuration to operate than standard "step/direction" type stepper motor drivers. We've provided functions to make configuring the registers in the L6470 chip much easier than it might otherwise be. Here they are, in no particular order.

Downloading the Library

The library is hosted on GitHub, along with the other design files associated with the AutoDriver board. To install the library and example code to your computer, download this zip file and follow these directions to install the library.

Initialization functions

There are two initialization functions (or "constructors", in C++ class-speke) provided for the AutoDriver library. You must invoke one of them to create an instance of class AutoDriver before you can use the board.

language:cpp
AutoDriver(int CSPin, int resetPin, int busyPin);
AutoDriver(int CSPin, int resetPin);

The two constructors provided allow you to specify which pins the particular AutoDriver boards are connected to. It is assumed that you will connect at least the reset and chip select pins; connecting the busy pin is optional, as the busyCheck() function will check either the pin state or the device's internal register to determine if the AutoDriver is busy or not.

These functions also initialize all the other SPI pins and hardware as appropriate; there is no need to invoke the SPI library or configure the SPI pins. It is, however, recommended that you use pin 10 as a chip select pin, since that pin must remain an output at all times in order for the library to function properly (this is a requirement of the SPI peripheral in the chip and cannot be changed).

Setting Basic Chip Parameters

There are many different parameters which must be set for the AutoDriver to function properly. These are stored in RAM on the AutoDriver and must be configured after every power cycle or chip reset.

Some of these parameters must be set for the chip to operate successfully; those parameters are described here.

void configSyncPin(byte pinFunc, byte syncSteps);

The BUSY pin on the AutoDriver actually has two possible functions: it can indicate when the board is BUSY (usually indicating that a motion command is underway and has not yet completed) or it can be used to output a sync signal for counting full motor steps with an external device.

There are constants defined for the two parameters: the first can be either BUSY_PIN or SYNC_PIN. If SYNC_PIN is passed, the second parameter should be one of the following:

• SYNC_FS_2 - two pulses on sync pin per full step of motor
• SYNC_FS - one pulse per full step
• SYNC_XFS - where X can be 2, 4, 8, 16, 32, or 64, and X indicates the number of full steps between pulses on the sync pin

If BUSY_PIN is passed, the second paramater should be zero.

void configStepMode(byte stepMode);

The AutoDriver is capable of microstepping, wherein the output signal is PWMed to create a pseudo-sine wave output which makes the transition from one step to the next less jerky. There are 8 possible microstep options, and defines have been provided for selecting between them:

• STEP_FS - Full-step mode; microstepping disabled
• STEP_FS_X - Enable microstepping with X microsteps per full step. X can be 2, 4, 8, 16, 32, 64, or 128.

Note that enabling microstepping has no effect on motion commands or sync pulse outputs; it is not possible to move less than one full step. Microstepping simply makes the transition between steps smoother.

void setMaxSpeed(float stepsPerSecond);

Provide an upper limit to the speed the driver will attempt to reach. Attempts to exceed this speed will result in motion being completed at this speed. The value established by this command will also be the value used for motion commands such as goTo() where no speed parameter is provided.

void setMinSpeed(float stepsPerSecond);

The minimum speed is slowest speed the motor will run. If low speed optimization is enabled (see below), minimum speed is automatically zero, and the special low-speed waveform optimization will be used until minimum speed is reached. Defaults to zero.

void setFullSpeed(float stepsPerSecond);

If microstepping is enabled, this parameter sets the speed above which microstepping is disabled and the driver engages full step mode.

void setAcc(float stepsPerSecondPerSecond);
void setDec(float stepsPerSecondPerSecond);

Set the acceleration/deceleration curves to be used. The maximum value for this is 29802; above that, the AutoDriver will not use any curve at all.

void setOCThreshold(byte threshold);

Sets the level at which an overcurrent event occurs. There are 16 different options; all take the format OC_XmA, where X is the limit and can be any of these values: 375, 750, 1125, 1500, 1875, 2250, 2625, 3000, 3375, 3750, 4125, 4500, 4875, 5250, 5625, or 6000.

void setPWMFreq(int divisor, int multiplier);

There's a separate internal clock for the PWM frequency used by the chip when microstepping or when KVAL settings (more on these later) call for a reduction in current. This frequency is 31.3kHz (nominal, when using the internal 16MHz clock), and is adjusted by the divisor and multiplier sent to this function. Again, we've created a set of defines for the possible values:

• For divisor, define syntax is PWM_DIV_X, where X can be any value 1-7.
• For multiplier, define syntax is PWM_MUL_X, where X can be 0_625 (for 0.625), 0_75 (for 0.75), 0_875, 1, 1_25, 1_5, 1_75, or 2.

It's a good idea to keep the frequency above 20kHz or so, to avoid annoying those in close proximity to the device, as lower frequencies can cause an audible ring or buzz.

void setSlewRate(int slewRate);

The slew rate is the slope of the voltage change coming out of the driver. There are three options here: 180V/us, 290V/us, and 530V/us. Higher slew rates increase the torque at higher speeds, at the risk of increased electromagnetic emissions, which may or may not matter to you. The defines for this are SR_180V_us, SR_290V_us, SR_530V_us.

void setOCShutdown(int OCShutdown);

By default, the drive transistors in the L6470 chip will shutdown on an overcurrent event to prevent damage to motor and driver. This can be disabled by passing the define OC_SD_DISABLE to this function, and re-enabled by passing OC_SD_ENABLE.

void setOscMode(int oscillatorMode);

This is one of the more important of the basic parameters. By default, the chip will run at 16MHz on its internal oscillator, and that suffices for most applications. However, in a situation where more than one AutoDriver is being used in a circuit, it's best to drive all of the boards from a common clock, so the motors will remain synchronized. That clock source can be either an external clock fed to the first chip and then passed along to subsequent chips, or it can be the internal clock source of the first chip, passed along to later devices. There are rather a lot of possible options here; we've created a verbose set of constants to help you select the right one:

• INT_16MHZ - Use the internal 16MHz oscillator, with no output on the OSCOUT line.
• INT_16MHZ_OSCOUT_2MHZ - Internal 16MHz, 2MHz on OSCOUT. Default.
• INT_16MHZ_OSCOUT_4MHZ - Internal 16MHz, 4MHz on OSCOUT.
• INT_16MHZ_OSCOUT_8MHZ - Internal 16MHz, 8MHz on OSCOUT.
• INT_16MHZ_OSCOUT_16MHZ - Internal 16MHz, 16MHz on OSCOUT. Recommended for the first AutoDriver in a system with more than one AutoDriver.
• EXT_8MHZ_XTAL_DRIVE - External 8MHz crystal. Not recommended.
• EXT_16MHZ_XTAL_DRIVE - External 16MHz crystal. Not recommended.
• EXT_24MHZ_XTAL_DRIVE - External 24MHz crystal. Not recommended.
• EXT_32MHZ_XTAL_DRIVE - External 32MHz crystal. Not recommended.
• EXT_8MHZ_OSCOUT_INVERT - 8MHz clock to OSCIN. Inverted OSCIN on OSCOUT.
• EXT_16MHZ_OSCOUT_INVERT - 16MHz clock to OSCIN. Inverted OSCIN on OSCOUT. Recommended for subsequent boards in a multi-board system.
• EXT_24MHZ_OSCOUT_INVERT - 24MHz clock to OSCIN. Inverted OSCIN on OSCOUT.
• EXT_32MHZ_OSCOUT_INVERT - 32MHz clock to OSCIN. Inverted OSCIN on OSCOUT.

Two things of note regarding the osciallator settings: first, if you select an invalid setting (for example, an external crystal in a system with no crystal), the AutoDriver board will stop responding. Because the settings are stored in RAM, however, a reset or power cycle of the chip will restore it to operation, allowing you to change your program to a supported clock mode.

Second, the frequency specified in this is used by the library to convert user-friendly units to units the chip understands. Using any frequency besides 16MHz will result in scale errors when setting speeds in steps per second, acceleration in steps per second per second, etc.

Advanced Chip Parameters

void setVoltageComp(int vsCompMode);

Voltage compensation attempts to keep the motor's behavior consistent across varying supply voltage. This is not as straightforward as it sounds, and users wanting to employ this functionality are urged to consider page 34 of the L6470 datasheet.

The defines to enable or disable this are VS_COMP_ENABLE and VS_COMP_DISABLE.

void setSwitchMode(int switchMode);

The switch input on the AutoDriver mode can be made to do one of two things: hard-stop the motor (for limit switch functionality), or perform user-based functions by exposing the switch mode to the user through an internal register. The constants to select between the modes are SW_HARD_STOP and SW_USER.

void setAccKVAL(byte kvalInput);
void setDecKVAL(byte kvalInput);
void setRunKVAL(byte kvalInput);
void setHoldKVAL(byte kvalInput);

The KVAL settings allow you to impose a global scaling on the current used for the four conditions listed above. The input ranges from 0-255, or 0% to 100% in steps of approximately .4%. This can be a good way to reduce the power consumption of your system if the full torque provided by 100% current operation is not required.

void setLoSpdOpt(boolean enable);

Low-speed optimization attempts to improved the zero-crossing of the driving sine wave at low speeds. When low-speed optimization is enabled (true passed to this function), the value set for minimum speed above becomes the speed at which low-speed optimization is no longer applied. When disabled (default, or false passed to this function), the minimum speed value is the lowest speed the driver will attempt to use.