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Author Topic: help whit signal step  (Read 1463 times)

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help whit signal step
« on: September 17, 2017, 10:35:39 PM »
I have problems with my CNC router, when checking the output signals of the LTP port I realize that when I move the motors of the axes, the signal indicates in which direction it has to rotate if it is activated but never stops sending output signal (the step) is never going to low.
I could help verify what is due, whether it is setup on the mach or is normal.
thanks for your help
Re: help whit signal step
« Reply #1 on: September 18, 2017, 12:46:59 AM »
Hi,
that sounds like the Direction signal not the Step signal.

If the Direction signal needs to be high to turn clockwise say then the DIR pin will go high and stay that way,
even once the move completes. If another move is initiated again clockwise the signal will stay high. If however
a move which takes the motor counter clockwise then the DIR signal will go low and stay that way until a new
clockwise move is called.

The Step signal pulses rapidly even when the motor is turning slowly and without an oscilloscope you won't
see it change, its just too fast. At best a multimeter will do some sort of 'average', maybe 2.5V.

Craig
My wife left with my best friend...
     and I miss him!
Re: help whit signal step
« Reply #2 on: September 21, 2017, 10:38:31 PM »
Hi craig:
As you say, if I can see that the direction signal in one direction goes high and stays that way even when its movement ends (Trajectory), just as you say if you go to the other direction you will go to a low signal and maintains it even if it is not moving.
However my doubt is with the signal of the stepper (pwm), because I do not know if the signal has to stay high (+5 V) even if the motor does not move, or if when its movement ends the signal is taken (0 - 0.8 V), I have been reviewing the stepper (pwm) signal with the oscilloscope and if it sends the clock signal, but I do not understand why when you stop moving the motor in one direction or another the signal is held high (+ 5V), should not be a low voltage?
Re: help whit signal step
« Reply #3 on: September 21, 2017, 11:04:39 PM »
Hi,
if you are probing the output of your BoB then its possible that the signal remains high because of a pull-up resistor
in either at the input of the BoB, the output, possibly opto coupled, of the BoB or the input of your driver.

My drivers require a low voltage when stationary but yours may differ. You need GOOD documentation for your
BoB and drivers. Do you have it and can you post it?

Craig
My wife left with my best friend...
     and I miss him!
Re: help whit signal step
« Reply #4 on: September 21, 2017, 11:26:33 PM »
Thanks for your help Craig, you're probably right because the diagram I got has both signals in pull-up, I recommend you change those resistors to pull-down?
Re: help whit signal step
« Reply #5 on: September 21, 2017, 11:52:07 PM »
Hi,
I dont think so, the CLOCK signal to the driver IC is active low, ie in inactive state its high. It s adequate as is.
What does puzzle me is that the base of the 2N2222s is not pulled to earth to ensure that leakage current doesn't
keep the tranistors conducting in absence of signal. I would be loading them to earth with 50k ohm or there abouts.

Craig
My wife left with my best friend...
     and I miss him!
Re: help whit signal step
« Reply #6 on: September 22, 2017, 12:32:22 AM »
The reason for the 2n2222 is for a single output signal from the LTP port gave +5V / 0.4mA, and to activate the opto led it needs 1.5V / 10mA so the add a stage of power, the problem was that the simulate circuit does not send the signal to the IC if the 33k resistor is in pull-down, besides the IC in the clock input requires 100 micro A the IC is the L297.
Re: help whit signal step
« Reply #7 on: September 22, 2017, 12:39:26 AM »
Hi,
certainly the 2N2222 is required for gain but does it actually switch off? Any stray capacitance in the base circuit
might mean that they don't turn off when the PP input goes low.

You are correct the 33k pull-up is required given that the L297 input is active low. I didn't propose that you pull it
down but rather the the base of the 2N222s.

Craig
My wife left with my best friend...
     and I miss him!
Re: help whit signal step
« Reply #8 on: September 22, 2017, 07:09:13 PM »
Certainly you are right I am not sure if the 2N2222 is turned off, if the observations before the led of the opto, has another led, that carried it has to indicate if it has signal of the entrance or not, however the carried one works of correct way of the side which is connected to the direction of rotation, but does not turn off the LED that is connected to the signal of the stepper (that signal is sent by the pwm of mach3), the most likely is that it stays on as you say, that you tell me to corroborate that it works that way.
Re: help whit signal step
« Reply #9 on: September 22, 2017, 07:23:01 PM »
Hi,
yes that is how I saw it as well. The step pulse stream is likely to be that fast that you will not see the indicator LED turn off, you'll need to
use a scope. But it did occur to me that in absence of any resistance to ground even modest circuit capacitance could hold the base conducting
and therefore the opto output would not change state and couldn't signal anything to the drive IC.

Craig
My wife left with my best friend...
     and I miss him!