[neric]

Hello,
My name is Neri while I am not a completely clueless in electronics I have some beginner level knowledge. I would like to have an LED indicator driven from the STEP output of my CNC controller so I will have visual feedback of axis movement I have tried some NE555 pulseting logic probe based circuites while they worked to some extand I never got enough lumination (brightness) from the LED and the results were far from what I needed. Then I have tried some Opamps circuites but with no success. The STEP port reading is averaging 0.25V fluctuating, the DIRECTION port reading is 4.85V
I was wondering if anyone has an idea or schematics that can accomplish this task, it should support 3 LEDs from 3 different pulse input(X, Y, Z axis) I just want the LED to detect the pulse
Please help

[Al_The_Man]

I would like to have an LED indicator driven from the STEP output of my CNC controller so I will have visual feedback of axis movement I have tried some NE555 pulseting logic probe based circuites while they worked to some extand I never got enough lumination (brightness) from the LED and the results were far from what I needed.

I suspect the pulse rate is too fast for the LED to indicate usefully that is why they are not illuminating as pulses.
I more ideal way is a simple rate counter in the form of a digital display.
What is the reason you want to know the pulse rate?
Al.

[neric]

Thank for the reply Al
I don’t need to know the pulse rate I just need t know that is pulsating. I need to know that there is a signal that going to the axis when I tried to take it from the Direction port I got a signal in CW and not in CCW so I figure I will get more constant signal from the Pulse (Step) port the reason I need this is when I look at the machine from a distance I would like to see an LED movement representation

[Khalid]

I see drawbacks of addition of LEDs...Wasting of valuable voltages / signals...

[neric]

Khalid,
I see your point. BTW the wood carving you do is AWESOME!!! and I appriciate your opinion...however I do need visual feed back system for my machine.
any ideas

[Eurisko]

How about this:

When a pulse is detected, light the led. If no more pulses arrive within the next second, turn it off. Easy with a microcontroller, could also be done with a cmos flip-flop and a 555 timer.

[neric]

Eurisko,
Thanks that what I was looking for low power application. Now I have no idea how to put it together if is not too much of a problem can you draw a schematics I don’t know how to work with logics ICs but I can read the schematics

[doorknob]

You may want to do a google search for "missing pulse detector".

You will probably find a number of 555-based circuits which might be suitable (you will have to pay attention to the timing-related components to get a good match to your step pulse rate, and you may need to handle things differently depending on whether your step pulse configuration is "active high" or "active low", but the sample circuits will probably help get you started).

[neric]

Doorknob,
Thank you very much!!
I will prototype this circuit and will see if it works for me. In regard to this I have a question the 1.1*R*C formula is this timing should repent the 35000hZ kernel I am using (mach3) or is that a setting for the visual pulse rate? When reading the documentations they said that the correct choice of should be 30% to 40% more of the pulse rate and I am wondering if it is the right ratio.

[Eurisko]

neric,

Try setting up the 555 (as a missing pulse detector) for a pulse train with a period of 1 second. The 35kHz kernel speed doesn't matter.

Your stepper controller will output pulses at a variable rate, depending on the axis speed at that time. The 555 should be looking for pulses each second, and turn the led off if no pulse is detected in its "1 second window". This will give a second of led "on time".

Here's a link to more 555 timer circuits:

LM555 Timer Circuits

Also, Forrest Mims has written numerous books detailing these 555 circuits. Radio Shack sells the books and the 555 timer, too.

Keep us posted, and I'll try not to overcomplicate things. Do we even NEED a flip flop???

[neric]

thanx,
I'll keep you posted ...hope it is going to work

[neric]

it is all working for my liking, so here it is I attached a zip file. the input is from the Step ports of the XYZ and the 5 VCC from USB port the LED might need 120 to 150 Ohms resistors Each, 1/8 W will be just fine.

[doorknob]

I do not think that the link to the zip file came through in your post...

[neric]

I hope here it is

[doorknob]

It's an interesting project, thanks for posting the info. You obviously put some good effort into building the circuit.

One thing that has me a bit mystified, though, is the back-to-back diodes on the 555 pulse inputs. I'm not sure that they perform any needed function in this application, but maybe I'm missing something.

[neric]

It is to protect against current back flow and reduse voltage

[Eurisko]

Well done, neric. Thanks for posting your results!

[mike_Kilroy]

.............
One thing that has me a bit mystified, though, is the back-to-back diodes on the 555 pulse inputs. I'm not sure that they perform any needed function in this application, but maybe I'm missing something.

hee hee!

yep. back to back series diode will do NOTHING for anything; now back to back ZENERS is another story of course....... make them like 15v and they will try to clip anything over +/-15v....

yepper.....

[Al_The_Man]

Back to back diodes are frequently use in various circuits, often as clippers.
The diode being a constant voltage source, the voltage across them will be the same regardless of current.
In this circuit it is most likely used to keep the input signal from driving the trigger to either Vcc or common.
Al.

[neric]

For all of ya Electronics buffs/gurus…me with my half baked knowledge in electronics I first prototyped the circuit and then when it worked I just copied it to a schematic nothing fancy just some garage knowledge and simple never went to collage logic….I believe if I did I will have better result in less time…in any event this is what I came up with. Shoot…it will be nice if someone who know his craft contributed to that…all I wanted to do is some civil service for some other electronics novice that might need this….I am very sorry if I confused you all.