Question about L297-8 and 555 timer circuit

[electron]

I just built up my board and connected the stepper motor. I am using this circuit to test the board out:



I am wondering if I have chosen the wrong 555 resistor values. When connected, the motor gets the HF whine (dogs go crazy) and it seems as if its moving very, very, slowly. As in, you barely notice it. Or, is this circuit totally wrong? When I use actual switches to enable and step the motor moves one step.

It's a bit late for me so I need some help!

[PMinMO]

You shouldn't let the 10K pot goto 0 ohms. Add a 470 ohm resistor in series. When the switch is in the 2.2K mode you might not get the motor started. Steppers really need to have a acceleration profile from 0 hz, and you would be better to change one of the resistors to 100K and set the pot to max resistance to get the mtor started.

[electron]

Ahhh... I was area of the acceleration profile of a stepper but did not realize it was that important. I put in my resistance substitution box and I was still unable to get the motor moving. I even tried full-coil or half-coil to no avail.

The 33uF cap on mine is not a polarized one so that might be the issue or my timer circuit is sloppy somehow. I should maybe breadboard it first and tinker with it some more.

This project is to make a turntable that rotates for an art project. So, I was hoping that the acceleration/deceleration thing would not be a factor.

Augh.

[PMinMO]

usually the 555 does a really good job on timing. I have a test box I use frequently that is simple 74HC14 RC oscillator, works like a champ, but you can dial the frequency down to fractional hz. Something like: http://www.piclist.com/images/www/hobby ... _ckt13.htm

[electron]

Damn... still is not working for me. Either the 555 or the other circuit you mentioned. I wonder if its my power supply as its a 24vdc/2.5a switch-mode type. The PS itself changes frequency as I try different freq's to move the stepper. I have another, identical one, I'll try that as maybe its a bad one.

sigh

[electron]

OK, i followed your T/S section on your Wiki. The outputs with power supplied and NOT enabled is near zero (like 200 mV). When I enable the outputs look normal. However, when i step they do not. They seem to be missing a step or I have to step twice maybe three times to get a voltage change from zero to supply voltage and back again. It will change just not always. This behavior is primarily on one channel.

So, Pminmo, do you think its the L297 or L298 or the 74HC14 chip?

[electron]

One of the three was bad, I suspect the L298... I originally used lead-free solder which has a much higher working temp. So, this time around I used leaded-solder and I can use the push buttons to step the motor. But, my 555 timer circuit just does not seem to work. It's always 60Hz on the output, which is probably line noise leaking in. And, I can't adjust that frequency at all.

[PMinMO]

if you socketed the L297 that's the easiest to swap and see if it fixes the problem. 99% of the time it's a solder joint. On DIY etch boards a tiny etch issue.

[electron]

You think this circuit would be better?

[electron]

OK... I figured out what it was with the 555 timing circuit: I forgot to connect Pin 7 to the two selectable resistors. As soon as I did that I was able to change the frequency and when I hit the enable pin the stepper started turning. Man... I can't believe it, a missed wire.

Whew!

P.S. I may have killed my first L298 by connected the motor with the power on. I think that's a sure fire way to kill the L298.

[PMinMO]

Yep, connecting a motor with power on is almost a guarantee to kill a driver ship.

[electron]

I also have a "cold joint" on a wire or somewhere which is the reason for the intermittent operation.

First cold join in like 8 years for me. I feel ashamed.

But, it works like a champ when it does!