Toms Easy CNC Stepper Motor Driver

You can build a 3 axis full step unipolar board like Tom's Easy for less than $30 in parts^ on a whiteboard or by etching your own PCB:

http://www.instructables.com/id/Easy-to-build-CNC-Mill-Stepper-Motor-and-Driver-ci/ Easy to build CNC Mill Stepper Motor and Driver circuits

The design is based on a pair of logic chips, the first one is a simple counter, and Tom has used it to generate logic 00, 01, 10 and 11 on two of the outputs. This is then fed to the second chip which converts it to 1000, 0100, 0010, 0001 which feeds the MOSFET transistors so turning each phase of the motor on in sequence. Another way of doing this is shown here: http://commons.wikimedia.org/wiki/File:Stepper_Motor_Driver_CD.png

There are a few limitations:

• It doesn't support microstepping so mid band resonance may be an issue.
• It doesn't regulate the current flowing in the motor other than by dropping power in the lamp. That means you must be very careful when selecting the bulb used vs the power supply voltage and motor rating. If you use a power supply that is more than a few volts over the rated voltage of the motor and the bulb doesn't glow when the motor is stopped, it will fry the motor.
• You aren't going to get really fast top speeds out of it, again, because you can't use a very high voltage power supply or a low voltage motors. It is better than a simple mosfet only driver, because the bulb does allow a higher voltage than what you could normally use.

Having said all that, they seem to work pretty well for Tom's little CNC mill design:

http://www.youtube.com/playlist?list=PL901E6AAC8BC660C3 Tom's Easy to build CNC video playlist

Part List:

Ref.    Qty	Description	
C1 Cap   1  Capacitor 10 volt or more and about 200 uf 	
Part No.      Mfg.      Source      Source Part No.
EEU-FC1J221   Panasonic Digi-Key 	P10346-ND

Ref.    Qty	Description	
R1 Res   1  Resistor 1000 ohms 
[if your voltage is > 15 volts this should be 1/2 watt or more]	
Part No.            Mfg.                   Source      Source Part No.
5073NW1K000J12AFX  Phoenix Passive Comp.   Digi-Key    PPC1.0KW-1CT-ND

Ref.    Qty	Description	
R3 Res   1  Resistor 100K ohm	
Part No.        Mfg.	  Source    Source Part No.
ERO-S2PHF1003  Panasonic  Digi-Key 	P100KCACT-ND

Ref.    Qty	Description	
Zener    1  Zener Diode [ Voltage regulator for ICs]	
Part No.      Mfg.       Source   Source Part No.
1N4735A-T   Diodes_Inc	Digi-Key  1N4735ADICT-ND

Ref.    Qty	Description	
D1-D4    4  Diodes [ to clamp voltage spikes]	
Part No.      Mfg.      Source     Source Part No.
1N4004-TP   Diodes_Inc	Digi-Key   1N4004-TPMSCT-ND

Ref.    Qty	Description	
U1       1  IC BCD Up/Down Counter 16-DIP	
Part No.      Mfg.            Source      Source Part No.
CD4516BE   Texas_Instruments	Digi-Key    296-2075-5-ND

Ref.    Qty	Description	
U2       1  IC Decoder CMOS BCD-DEC 16-DIP	
Part No.      Mfg.            Source     Source Part No.
CD4028BE   Texas_Instruments	Digi-Key   296-2045-5-ND

Ref.    Qty	Description	
Q1-Q4    4  MOSFET N-CH 100V 12A TO-220AB	
Part No.      Mfg.                  Source     Source Part No.
RFP12N10L   Fairchild_Semiconductor	Digi-Key   RFP12N10L-ND

Ref.    Qty	Description	
R2       1  "Lamp Socket [Hldr, Lamp; Wedge; PCB; 23 Series]"	
Part No.      Mfg.                           Source	          Source Part No.
23-35 (PC)  Lighting_Components_and_Design  ALLIED Electronics  931-2335

Ref.    Qty	Description	
Conn.    1  Connector 25 Pin D-Sub Male [You need this to connect to the computer]	
Part No.          Mfg.	           Source    Source Part No.
171-025-113R001   Norcomp_Inc.     Digi-Key   4225ME-ND
						

Possible Improvements:

• Use a cheap uC (e.g. Arduino, PIC, etc...) to generate the drive sequence instead of the logic chips, and switch to half step, or even perhaps microstepping via PWM.

  .