27938 datasheet, PDF - EEWORLD Datasheet

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27938: Descriptionmotor controller little step-U; CategoryModule/solution; File Size53KB，12 Pages; ManufacturerParallax Inc.; Websitehttps://www.parallax.com/

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motor controller little step-U

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Little Step-U

Unipolar Stepper motor controller

Description

CON 1

CON 2

COIL A

COIL B

COIL C

COIL D

CT - AC

CT - BD

CON 3

2.0 in

/IP1

/IP2

BUSY

SERIAL OUT

SERIAL IN

Vcc (+)

GND (-)

The

Little Step-U

is a complete, serially

controlled, drive system for unipolar stepper

motors. Using an intelligent module allows the

host system to concentrate on the task at hand

while the

Little Step-U

performs all calculations

and operation of the motor.

The desired operating speed, ramp time and

drive mode can be configured once and then a

single command used as required, to move to

fixed or relative positions. While the motor is in

motion, a BUSY output is active and the

movement can be optionally interrupted by one

of the two external inputs. The position of the

motor is maintained in a readable register which

can be set to zero (Home) by a command or

when an input is activated. A similar register is

available to save a second position (Mark) either

by command or from an input. These points

can then be referenced directly with a 'Move to

home' or 'Move to mark' command.

A built-in ramping function accelerates the

motor from a standstill to the desired speed over

a specified time period, allowing faster final

speeds to be achieved, and also to decelerate

the motor to give maximum load braking. When

the motor is stopped, a command specifies

whether the windings are left energized (for

maximum holding torque) or turned off (for lower

power consumption / dissipation).

A remote function is included for use in more

complex systems. Once activated, the two

external inputs become STEP and DIR, with the

motor stepping in the indicated direction with

every pulse applied to the step input.

Vom (-)

Vm (+)

1.0 in

Features

•

Unipolar motors to 35V, 3.0A

Full step, half step and wave drive modes

1-5,000 steps per second

Inbuilt speed ramp (0.1-20.0 seconds)

Simple serial commands (TTL interface)

Separate power input for motor and logic

Suitable for direct and L/R operation in all

modes

On board clamping diodes

Current position register (+/-100,000,000)

Zero position and user marker registers

Absolute & Relative movement commands

Busy output

Two inputs suitable for optical stops

Slave mode using inputs for STEP & DIR

Stop with motor coils on or off

CT-AC

CT-BD

Vcc

Logic Signals

Microcontroller

GND

Vom

TLA Microsystems Ltd

http://www.tla.co.nz

Hardware Connection

Power Supply

The

Little Step-U

divides the circuitry into two distinct sections with separate power supplies

required for the motor drive and the logic. The logic/control section must be powered by a

regulated 5V supply applied to the VCC and GND pins. The motor power supply voltage is

dictated by the motor characteristics and is connected to the VM(+) and VOM(-) pins. The

GND and VOM pins are connected on the circuit board as a common reference. The motor

power supply must have sufficient capacity for the motor and if the power supply is not

physically close to the motor/controller, a capacitor (eg. 4700uF) may be required at the

controller to ensure smooth operation of the motor.

Motor Connection

The motor connector has 4 connections (A, B, C & D) that are switched to ground in the

sequence required to cause the motor to step. Note that stepper motor manufacturers have

several methods of labelling the connections to the motor. The

Little Step-U

labels the pins in

the sequence they are switched when operating the motor with one coil on at a time and driving

in a clockwise direction. ie. A, then B, then C, then D and back to A. The centre taps of the

two coils are connected to CT-AC and CT-BD, corresponding to the common connection of coils

A & C and coils B & D respectively. These two connections provide the freewheel diodes for

each of the motor coils and are connected on the circuit board.

IMPORTANT: A poor or intermittent connection to any of the stepper motor terminals can result

in destructive voltages being generated and causing permanent damage to the Little Step-U.

Similarly, do not connect or disconnect any stepper motor connections while power is applied.

The connection point between CT-AC and CT-BD is indicated on the circuit board by the

designator "LK". This track can be cut and rejoined by soldering a wire between two pads if

needed. In most cases this isn't required but is provided for applications using and L/xR

configuration in half step mode.

Interface connections

The Little Step-U acts on commands received serially from a host controller via the SERIAL IN

pin. This is an asynchronous interface operating at 2400 bits per second, 8 data bits (LSB

first), 1 stop bit and no parity. The signal levels are TTL. Some commands illicit a response

and these are sent via the SERIAL OUT pin using the same protocol and signal levels as the

SERIAL IN pin.

When a command has been sent to the Little Step-U that causes the motor to move, the BUSY

pin will be high while the motor is in motion.

Two input pins are provided for use with stepper operation in the form of limit or home switches

or can be used as general inputs which can be read by software. These pins accept logic level

inputs and will source 1mA when pulled low, making them suitable for direct connection to the

output of opto-couplers.

TLA Microsystems Ltd

http://www.tla.co.nz

{C2}

Half step

Each alternate step has one or two windings energised giving the motor twice

the number of steps per revolution.

Step

Coil A

Off

Coil B

Off

Coil C

Off

Coil D

Off

When the mode is changed to or from Half step, the position, mark and speed values are

adjusted accordingly so that the motor will turn at the same rotational speed and the

mechanical positions remain unchanged.

Example: A 200 step/rev motor is being used. The current position is 3600, speed is set

at 200 steps per second and there is a mark at 1200. When the mode is changed from

full-step to half step, the speed value will be 400 (giving the same number of revolutions of

the motor per second). The current position register and the mark register will contain

the values 7200 and 2400 respectively.

- GO TO ABSOLUTE POSITION

Syntax

{Dxxxxxxxx}

At anytime after powerup, the Little Step-U keeps track of its current position in steps.

This command instructs the Little Step-U to calculate the direction and number of steps

required to move to another position and then it performs the move. At the end of the

move, the position will be the number specified in this command. The value can be any

number from -10000000 to +10000000, including 0. The number may be preceded by a

"+" or "-" as required, but must not include a comma or decimal point.

Example: If the current position is 2500, a command of {D-1000} will cause the motor to

run counter-clockwise for 1500 steps, stopping at position 1000.

- GO TO RELATIVE POSITION

Syntax

{Exxxxxx}

This command is similar to the "D" command in respect to the numeric parameter, but

commands the motor to move to a position relative to its current position. Positive

numbers are clockwise and negative numbers are counter-clockwise.

Example: If the current position is 2500, a command of {E1000} will cause the motor to

run 1000 steps clockwise to end at position 3500.

- GO TO ABSOLUTE POSITION WITH INPUTS 1 & 2 AS STOPS

Syntax

{Fxxxxxx}

This command is the same as the "D" command except that the two input pins are

monitored. If either of them is pulled low during the move, the motor will be decelerated

to a stop at the rate defined in the RAMP command (B). The position register will reflect

the current position when the motor has stopped. These inputs are level sensitive so if a

“F” command is used when one of the inputs is low, the motor will stop immediately.

Note: Allowing the motor to continue to running past a stop indicator is done for two

reasons; This method allows the motor to provide maximum braking torque during

deceleration and the position register integrity is maintained.

TLA Microsystems Ltd

http://www.tla.co.nz

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