µC Stepper Control 2

by Martin Clausen (mc AT rotgradpsi DOT de)

This circuit employs a MCU to control up to two bipolar stepper motors via RS232.

Not recommended for new designs, for reference only, please use Stepper Control 2 Plus instead!

• Features
• Usage of Device
• Parts
• Driver IC Recommendations
• Download of Program and Circuit

Features

• three phase movement: acceleration, constant speed, decceleration
  
• drives up to two bipolar stepper motors
• each motor can be driven independently in full step, half step or quarter step
• constant torque in full and half step mode
• up to 10,000 steps per motor and second
• 0 to 9999 steps per command, in version A 0 to 65535 steps per command
• 0.1 to 9.9 ms time between steps
• parameters of motion can be set for each motor separatly
• 8 general purpose in-/output lines
• support for reference switches
• up to 255 devices cascadeable, also compatible with the whole control familiy
• all commands from the computer pass through with a delay of only 29µs plus send time of one character, while no motor is running
• 128 bytes communication buffer
• RS232 interface, 8 databits, no parity, one stopbit
• supported baudrates: 115.2; 57.6; 38.4; 19.2; 9.6; 4.8; 2.4 and 1.2 kbps
• line end character: CR; other possible, please send me a mail
• LED shows activity
• low cost, low part count
• Labview driver supports relative and absolute move in "real word" units, home search, set parameters, read and write GPIO
• Program is freeware for non-commercial use.

Usage of Device

Address and line end character can be changed easily, just send me a mail with your demands.

The LED will be on after power-up. After each correct command it will toggle between on and off. If a buffer overflow occurs, the LED will stay permanently off and the MCU is stopped.

The hold jumper is used to switch off the hold current through the motor coils, while both motors stand still. A closed jumper corresponds to no hold current. The jumper is read every 100µs. If you want to control this pin via RS232 you could use a GPIO pin. There is no direct control of this feature via software, because in some application the motors might be driven with a higher current than allowed for infinite time because of too high power dissipation. Since in this case wrong settings might damage the motors this option is normally not accessible via RS232.

The GPIO lines are located at P1 of the MCU. They are open collector outputs with a weak pull-up resistor and contain also a circuit for read back. Refer to the microcontroller datasheet for details. The state of the GPIO after reset is high. Note that you need to write an one to a GPIO before it is possible to use it as an input, if it has been used as an output since the last reset.

If you send a new command while the old one is still executed on the same motor, the controller will change to the parameters of the new command, without the full execution of the previous command. If this occurs, a calculated position on the PC will not match the real position.

Messages from the controller are sent with its own address first and then followed by the data in hex-code (nibble by nibble from msb to lsb).

Note, that due to the limitations in computational power and number of timers, the motion profiler increases and dereceases the steptime linearly. In case of a long acceleration/deceleration time (maximum steptime > 3*steptime) this leads to large derivation from an almost linear to hyperbolic velocity profile and smoth motion without the loss of steps is not reached. See µC Stepper Control 2 Plus for a version for a single bipolar motor with a more advanced motion profiler.

Comand Structure

Baudrate Selection

Meaning of 1 and 0 in this table:

Sign	Switch
1	closed
0	open

The baudrate jumper are read up on reset.

Parts

• Semiconductors:
• 1 AT89C52 or AT89S52, 24MHz; see also programming tips
• 1 MAX232
• 1 set of drivers, see below
• 1 78L05
• 1 low current LED

  Capacitors:

• 1 1µF / 25V axial
• 6 10µF / 25V axial
• 2 33pF cer
• 3 100nF cer

  Resistors:

• 2 4,7k*8 / 9 pin sil array
• 1 1k

  Mechanic:

• 1 22.118MHz crystal
• 2 sub-D socket, 9 pin
• 1 dip switch with 4 switches
• 1 case
• 1 pbc
• 1 some thin wire
• 1 socket 16 pin
• 1 socket 40 pin
• 1 loop back plug (9 pin plug with only pin 2 and 3 connected to each other) for the last controller in a chain only

Driver IC Recommendations

Download of Program and Circuit

• stepper2.hex MCU program V4, address "B"; see also programming tips
  if you need another address, please mail me
• stepper2a.hex MCU program V5, version A, 0 to 65535 steps per command, increased command length by one byte, values form 65536 to 99999 warp around, address "B"; see also programming tips
  if you need another address, please mail me
• stepper2.gif circuit V1.01, for both versions
• steppercom2.html communication protocol for stepper2 V4
• steppercom2a.html communication protocol for stepper2a V5
• stepperzero.html protocol to find the mechanical zero with one reference switch connected to ref sw and GPIO.0, for both versions
• stepper2lv.zip LabView driver V1.01 for stepper and stepper2 V4, for home search connect reference switch to ref sw and GPIO.X, where X is the motor no. In case of several reference switches decouple them via diodes. Can easily be adjusted for A version.

The part description in schematics is read as follows:
part type + value in exponential form + package description + subpart number in package
for example: C1040805,1 means Capacitor, 100nF, package SMD 0805, first subpart in package

Disclaimer: No warranty at all!
Copyright by Martin Clausen, Germany.
Contact the author: mc AT rotgradpsi DOT de
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