Unipolar stepper motor with ULN2003?

[musicworld1]

hi

Last time I was designing like this . I attack this to computer before start computer. After start I write codes and run only 3 steps. I find that IC and motor are going very much hot, then I disconnect all connections to IC. It really was near to be burnt, if I do not disconnect. What was the problem in circuit? I think it may be in its ground or +12V wire. Is it?

[Tweakie.CNC]

You need to current limit the supply to each coil to ensure it doesn't exceed 500mA per driver (series resistors in line with pins 13 - 16). Also you may need to heatsink the ULN2003.

Remember - the computers printer port (LPT) is fragile and it is always best to use a buffered or opto isolated BoB when experimenting like this.

Good fortune and don't make expensive smoke 

Tweakie.

[musicworld1]

I have found the reason not the solution, it is that I am using the computer power supply. The +12V point has 6 Amp, as written on info sticker of computer power supply. But ULN2003 require only 0.5 Amp, that’s why my whole system was getting so much hot. But how to arrange the correct power supply (12V & 0.5 Amp). Which is cheep & easy source?

[Tweakie.CNC]

I thought I had already given you the solution :- "You need to current limit the supply to each coil to ensure it doesn't exceed 500mA per driver (series resistors in line with pins 13 - 16). Also you may need to heatsink the ULN2003".

(Some basic maths shows that if you are using a 24 volt power supply you need to put a 24 ohm 6 watt resistor in series with each of the pins 13 to 16). 

Tweakie.

[Tweakie.CNC]

Correction to above:-

(Some basic maths shows that if you are using a 12 volt power supply you need to put a 24 ohm 6 watt resistor in series with each of the pins 13 to 16). 

Tweakie.

[musicworld1]

I find some thing written on my motor. That is:
60C 45
5 DEG 13 (ohm) MAS
You can also read more about this motor from http://www.compucanjes.com/products/view/14268.html. what is basic formula to set at any system.

[Sage]

If you wish to drive the motor windings with the maximum current of 0.5amps with a 12v supply you willl require 11ohms in series with each winding.

(12-(0.5x13)) / 0.5

The motors will not have much speed or power driven like this tho.

Sage

[Tweakie.CNC]

Well done Sage for getting it right - I forgot to subtract the motor coil resistance, and I had two goes at it 

(My tutors always said that the degree in Mathematics and Computing was wasted on me - I think they were right  )

Tweakie.