Monday, 13 February 2012

Stepper motor drive

Stepper motor drive
Integrated circuits intended to drive stepper motors are many and are rather easy to operate because they contain both logical circuits and power circuits in the same chip. You just have to choose the circuit corresponding to the type of stepper motor you want to use, namely unipolar (6 wires) or bipolar (4 wires).
In the first case, we can use a SAA on 1027 (difficult to find now) or a more powerful UCN 5804. For the bipolar motor, the SAA 1042 (idem) or the MC 3479 will be quite indicated. Most of these controllers allow to work in half-step mode.
It is to note also that we can drive a unipolar motor with a controleur for bipolar motor but that the opposite is not possible.
We propose here a plan of driver for unipolar motor realized with 2 common logic components and a power circuit. It is possible to drive motor needing 500 mA by coil, what should be sufficient in the present frame!
Pin Assignments for CD4070
  1. In 1
  2. In 1'
  3. Out 1
  4. Out 2
  5. In 2
  6. In 2'
  7. Ground
  8. In 3
  9. In 3'
  10. Out 3
  11. Out 4
  12. In 4
  13. In 4'
  14. +Vcc
Pin Assignments for CD4013
  1. Out 1
  2. Out inv 1
  3. Clock 1
  4. Reset 1
  5. Data 1
  6. Set 1
  7. Ground
  8. Set 2
  9. Data 2
  10. Reset 2
  11. Clock 2
  12. Out inv 2
  13. Out 2
  14. +Vcc
Pin Assignments for CD4093
  1. In 1
  2. In 2
  3. In 3
  4. In 4
  5. In 5
  6. In 6
  7. In 7
  8. Ground
  9. +Vcc
  10. Out 7
  11. Out 6
  12. Out 5
  13. Out 4
  14. Out 3
  15. Out 2
  16. Out 1


Components list
IC :
quad. XOR = CD 4070 or 4030
Dual shift register = CD 4013
Ampli = ULN 2003
Unipolar stepper motor

Stepper motors can be found on old floppy disk drives or printers for example. In certain cases we can even use the controllers who are joined to it. 2 control pulses can result from a microcomputer (parallel port) + line buffers.
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Analogic / Digital converter

Analogic / Digital converter
This integrated circuit (AD 7821) allows to convert an analogic signal in a 8 bits value with a 1 µs conversion time, thus with a 1 MHz frequency. There are faster converters allowing to obtain a better resolution (10, 12, 14 or 16 bits).

Pin Assignments for AD7821
  1. Input
  2. Data bit 3
  3. Data bit 2
  4. Data bit 1
  5. Data bit 0
  6. WR/RDY
  7. Mode
  8. RD
  9. INT
  10. Ground
  11. Vref -
  12. Vref +
  13. CS
  14. Data bit 4
  15. Data bit 5
  16. Data bit 6
  17. Data bit 7
  18. OFL
  19. Vss
  20. +Vcc


Components List
Pot. : P1 = 20 kΩ
A/D Converter = AD7821
trigger inverter = 1/4 CD4093
The signal resulting from the amplifier is applied to the pin 1 (Input). The reference voltage is adjusted by means of P1. It is very summary but that works. We can also use a specific component to obtain this reference voltage (zener diode for ex.).
The pulse "start of conversion" results from the clock generator (having a 5 V level compatible with the converter) and the pulse "End of conversion" is sent to the PC interface, as well as 8 bits data. We can also send these data through buffer circuits (74245 by eg) to secure the exchanges interface-converter. The logic gate (1/4 CD4093) can be another inverter.
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