well then check the gbrl forum and see if anybody there knows how to pwm an output. would be much easier to do in SW than modifying your shield.

 

That is very good advice, thank you. I agree if u can do it software wise then that's much better. Say I get it right. How do I determine what analog write to do to get 600ma ? Is there a formula?

 

you might want to just play around with the numbers and measure the current. I would start somewhere around 18% PWM because 100% (full on) gives you 3.4A, so proportionally, 18% should give you .6A.

 

Hello guys,

I am new to electronics i have been playing around with them for some time.

I have recently started up a new project, i want to build a cnc router.

I have build a h bridge on a bread board and that seemed to work. But now i have build one onto proto board and i am having some trouble.

I am using tip-122 (npn) and tip-127 (pnp),

here is the schematic that i based my design on.

http://www.pocketmagic.net/wp-content/uploads/2009/03/hbridge-radu1.jpg

For a stepper motor i needed two of these h-bridges for each motor as each h-bridge controls a coil. (im using bi-polar steppers). the control signals (input) comes from an arduino.

The problem that i am having with my 1st attempt is that when i put in my power source (for the h bridge) even 5v now to test, the transistors are getting warm.. and i cant find out why?? (even with no motors or inputs connected).

I left out the diodes from the schematic as i thought they are for dc motors which might spin and cause feed back power, but that shouldnt happen with steppers? are these necessary?

Only thing that i can think of is that both the halves of the h bridge are "enabled" and power is shorting directly from the pnp to the npn. ( even with no motor connected)

Could this maybe be from the smaller transistors picking up voltage and enabling the 4 tip-122 and tip-127 transistors??


Please if any one could give me some assistance, I dono if the info i have given is sufficient, but it will be greatly appreciated!

Thanks

i'm using that same design to control a stepper motor, u said you need one h bridge for each coil. the only thing is, i'm confused about how there are two inputs to that circuit. I'm using a signal generator and sending a square wave through it. do i ground the other input. Do you have a schematic of how u hooked up the motor to the two drivers that would really help and be greatly appreciated.