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Chinese breakout boards (flipping signal?)
« on: January 01, 2015, 12:58:18 PM »
This is my first post on this forum. I used to use Yahoo forum long time ago (equals to +10 years) when I started with Mach (maybe 1). For a certain reasons I've been recently quite lazy with my CNC applications and naturally with Mach as well. However, recently I found a small CNC mill (Terco CNC 45) which I rescued and placed it into my basement thinking to rebuild it.

I got a Chinese breakout board for the project and my questions concerns exactly that one.
I cant find any manual for it but if I paste some links here about it, maybe someone can recognize it (from another forum)

Somebody on that forum says that he/she had managed to get the thing working. However, I have not had that much good luck.

The problem I have here is, that the board converts my signal (flips it upside down). I get pulses nicely in to the board, but the smith triggers (those three chips) sneaking on the board are giving a halterneck to the signal throwing it upside down. this signal is then something the stepper driver do not understand and it does nothing.

If I change active low in mach configuration, everything on the BO board works fine till the optocouplers. A very short negative pulse does not seem to come through.

If the BO bord is really functioning like it designed to, I just can't get what I'm doing wrong.

I'd really appreciate if I could get some hints for this.

I was thinking to try by replacing smith triggers with non-converting ones. But at this stage it'll take time since all stores (selling chips) are closed till 7th Jan due to a holiday season.

(from Finland)
« Last Edit: January 01, 2015, 01:01:06 PM by justjuha »
Re: Chinese breakout boards (flipping signal?)
« Reply #1 on: January 01, 2015, 05:58:05 PM »
Hi Juha,

Unfortunately, the breakout board is probably not doing what you want. Many of the Chinese breakout boards use opto-isolators that are slow or not biased correctly.

What is happening is that the opto-isolator cannot turn on and off quick enough.  On some of these boards, the optos are biased with a resistor of a too high value limiting the current to the opto, so the diode in the opto never gets a chance to turn on before the pulse turns off (or visa-versa). This can sometimes be fixed by substituting the resistors with appropriate values. There are a number of threads on the CNCZone where people have done this.

The other problem is that the board may be using a slow opto that will not be capable of switching on-off or off-on fast enough. For that you would need to replace the optos with faster ones.

My suggestion is to buy a decent opto-isolated breakout board.PMDX at http://www.pmdx.com/ designs and sells quality breakout boards.

The fact that the board inverts the signals from the PC is quite normal. The parallel port of the PC sits at logic hi in it's rest state, so that having a logic hi as "off" in the breakout board is common.


Homann Designs
email: peter at homanndesigns.com
Re: Chinese breakout boards (flipping signal?)
« Reply #2 on: January 02, 2015, 05:45:04 AM »
Thank you Peter for revealing the truth about cheap & d..y.
BO board you suggested looks nice and it looks there is a thread in this forum about preferred boards. It looks like there is getting to be also Ethernet based solutions available at the same price range your reference is at. Maybe I need to read something about these "Ethernet smoothsteppers" before I buy any new gadgets.

Anyway first Im going to try by replacing existing SN74HC14 to 74HC7014 non-inverting chips.

But certainly it would be nice to hear more comments from the experts whether it is advised to go for ethernet instead of lpt or usb ports


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Re: Chinese breakout boards (flipping signal?)
« Reply #3 on: January 02, 2015, 07:17:37 AM »
Ethernet is the way to go for an external controller, it is much more robust than USB and is an industry standard.

The ESS is good but also look at the CSMIO/IP-M, it looks more expensive but when you consider that it has analogue I/O for spindle control etc and no need for a breakout board as it is integral, then it actually may be cheaper. Only thing is the limitation of pulserate (125KHz) but for a stepper system that is not a concern.

Re: Chinese breakout boards (flipping signal?)
« Reply #4 on: January 29, 2015, 06:09:47 AM »
Ok, now I've gone for CSMIO/IP-M, and the results can be seen in an other thread.

Something to learn, but at least looks a bit more promising comparing to application with those Chinese BOBs.