acorn output wave form

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pulsenpal
Posts: 27
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acorn output wave form

Post by pulsenpal »

I am bench testing acorn board--

using pocket digital recording ocilloscope which has been of great value in
analysis of heidenhain encoder output waveform documentation as I proceed with retrofit of
romi 20x40 lathe (was bridgeport ez-path)

problem is I am not getting output at step/direction pins

wizard is set to benchtest mode

any thoughts?

thanks

pulsenpal


GOOGLE pics link

https://photos.app.goo.gl/R0VxKVul4IzAZ1fS2
pulsenpal
Posts: 27
Joined: Sat Dec 09, 2017 1:33 pm
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CPU10 or CPU7: Yes

Re: acorn output wave form

Post by pulsenpal »

problem solved

I connected pos clip to +24 vdc input and - clip to step output 1

got proper waveform which varies nicely with feedrate vcp toggle

also note 21 vdc output which is not compatable with 5 vdc input step/direction on my superior 2000 d6
step drives--so will run 6 vdc power thru input header for output to drives

i will power proximity sensors seperately for limits

new pics
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cncman172
Posts: 254
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Re: acorn output wave form

Post by cncman172 »

Pulsenpal,

I hooked up my Fluke 50MHz scope meter to the Acorn and had a great deal of difficulty getting a nice square looking pulse coming out of the Acorn. I connected to ground and the Step Output. I even tried to make it a constant waveform by issuing an MDI command of G1 X5 F.25 which is a very slow rate but it would be a constant output. What I even up with is something that looks more like an AC wave with negative pulses riding on the AC signal. I then connected a Fluke digital multi meter to the Step Output and tied the other side to common. When I would jog that given axis I would get a negative -.100 volts or something close. As soon as I would stop the voltage would go to zero.

This seems to imply the pulse stream coming out of Acorn is a negative pulse stream, when I use the +24V as the common I get the same results but the voltage is of course a higher negative voltage.

This could have led me onto an issue I have with my Acorn not following the numbers of pulses exactly. My servo amplifiers are expecting a positive pulse stream and that could be causing me issues. Someone from Centroid posted the waveform should be a symmetrical waveform of 250uS.

The Pulse stream coming from the Acorn should be a TTL level not 24V. The 24V on the Acorn gets down converted on the Acorn board to lower voltages and should be able to provide step and direction to the superior drives. I have some of those old drivers myself.

Russ
cncman172
Posts: 254
Joined: Thu Nov 02, 2017 4:07 pm
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Location: Westerville, Ohio

Re: acorn output wave form

Post by cncman172 »

Pulsenpal,

After looking at the spec page on the Acorn the outputs are Open Collector type they are pulled up to +24V but the outputs go low when activated, look at the schematic on page of the the spec manual. This is why you had a better view on your scope when you connected the common to +24V.


Russ
cncman172
Posts: 254
Joined: Thu Nov 02, 2017 4:07 pm
Acorn CNC Controller: Yes
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CNC Control System Serial Number: 985DAD429EE9-0926170118
DC3IOB: No
CNC11: No
CPU10 or CPU7: No
Location: Westerville, Ohio

Re: acorn output wave form

Post by cncman172 »

Pulsenpal,

I just got my machine working perfect. If you want to drive a stepper drive like you have use the DB25 connector on the Acorn which is setup to drive a Gecko G540. The Gecko G540 was designed to be driven by the parallel port, so the outputs from the Acorn had to be at positive TTL levels. Sure enough if you use pins 2,3 for X, 4,5 for Y, and 6,7 for Z you will find it works perfect.

Russ
pulsenpal
Posts: 27
Joined: Sat Dec 09, 2017 1:33 pm
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Re: acorn output wave form

Post by pulsenpal »

cncman

appreciate the comments

the db-25 configuration gives me what I need but I do not want to use a breakout
if avoidable--------- pin and socket connectors are to be avoided if possible

opto-isolators are voltage sensitive in my experience--so I connected a 5 vdc wall wart
to acorn and get precisely what I need wave profile is not square but should work as trigger

Marty's excellent videos note his use of 5 vdc for step driver logic/opto components

open collectors at 24 vdc may satisfy step/direction needs for control logic but cannot be used in opto-isolator
control in my experience

in pics just posted note the voltage grid base dropped to 2 volt units and the frozen signal contour
of 100 microsec the 2000 d6 step driver requires a 0.4 microsec signal base as pulse trigger
signals other than pulse require 50 microsec base width
from the frozen profile in the pic--this requirement should be met

also note documentation of high/low direction voltage swing of 4.7 vdc
btw--the pocket dso is a new product priced less than $75 usd and fits into the smallest workspace
as I puzzle out machine control :)
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martyscncgarage
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Re: acorn output wave form

Post by martyscncgarage »

Go to the advanced tab on the wizard and invert the signals and play with that on your scope.....
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
eng199
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Re: acorn output wave form

Post by eng199 »

pulsenpal,

The ACORN screw terminal outputs do not have pull up resistors. This means the outputs are either pulled to GND or not pulled to GND. There is no voltage to measure if nothing is connected. What you are seeing is due only to stray capacitance. To get a good scopeshot, put a 2.2k resistor between the output and 24V. Always connect the 'scope ground (- clip) on ground. Any other method is confusing and potentially damaging if your 'scope is not isolated.

Take a look at page 3 of the user guide:
http://www.centroidcnc.com/centroid_diy ... manual.pdf
There is an example of how to connect your drive. The only difference is the "external power supply" in your case will be 5V.

Page 14 of your drive manual has a similar diagram, where the transistor shown will be the ACORN output transistor.
http://repair.motorsystems.com/wp-conte ... manual.pdf
I connected a 5 vdc wall wart to acorn
If you used 5V to H9 for the ACORN power, it will not boot. The ACORN is designed to work from +24V logic power. Anything else will certainly cause problems.
pulsenpal
Posts: 27
Joined: Sat Dec 09, 2017 1:33 pm
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Re: acorn output wave form

Post by pulsenpal »

eng199

thanks for the comments
I introduce the 5 vdc power into header h4 in terminal labeled 24 vdc
I do not alter input of 24 vdc into mh7 mains power
I am unable to find connector with label h9--which brings up point that
not one of the centroid drawings has the headers labeled as silkscreened on board--this is
a serious oversight in process of referrencing connections and debugging

my earlier comment regarding opto-isolators I judge to be valid--that is
5 vdc input is more appropriate than higher voltage open collector circuitry

appreciate the insight
martyscncgarage
Posts: 9912
Joined: Tue Mar 28, 2017 12:01 pm
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Location: Mesa, AZ

Re: acorn output wave form

Post by martyscncgarage »

pulsenpal wrote: Mon Dec 11, 2017 10:19 pm eng199

thanks for the comments
I introduce the 5 vdc power into header h4 in terminal labeled 24 vdc
I do not alter input of 24 vdc into mh7 mains power
I am unable to find connector with label h9--which brings up point that
not one of the centroid drawings has the headers labeled as silkscreened on board--this is
a serious oversight in process of referrencing connections and debugging

my earlier comment regarding opto-isolators I judge to be valid--that is
5 vdc input is more appropriate than higher voltage open collector circuitry

appreciate the insight
Pulsepal,
H9 is the power input terminals, H9 IS screened on the board. between the right edge of the terminal block and the lower right screw mounting hole. See attached drawing. Drawings are quite clear and Acorn's terminal blocks are laid out per the drawing.

I would NOT put +5VDC where it calls for +24VDC.

Centroid's engineers have been designing and building motion controllers for over 30 years. I trust they know what they are doing.

What is the purpose of what you are trying to accomplish?
Marty
Attachments
S14826-ACORN STANDARD CONNECTIONS.pdf
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Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
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