Inverse Output Pin

[theminor]

This is probably simple, but I can't figure it out.

I'm re-arranging my controller using a very simple BoB on the second parallel port output from my smoothstepper. I'm setting one of the outputs on this Port 2 to control my spindle relay (on/off). I've got my power ground running to (-) on the relay and the output pin on the BoB running to (+) on the relay. In mach, everything works fine. M3/M4 turn the spindle on just fine.

The problem is that when I exit Mach, when power to my controller is still on, the spindle turns on. So when I exit Mach, the Spindle turns on and stays on until I turn off the power to my controller. Similarly, if I turn on my controller while Mach is not running, the spindle turns on.

This tells me that the output pins on my cheap-o BoB are normally high. When mach comes on, the outputs go low, and Mach controls it properly, sending them high when it gets an M3 code.

I need this output pin to be low by default, not high. Would a pull-down resistor accomplish this, and if so, how do I determine what value resistor to use? There is virtually no documentation on this cheap-o BoB, except this: http://kelinginc.net/KL-DB25.pdf

Thanks in advance for any help!

[keebler303]

It is recommended to power up your machine like this: Computer>Mach>Machine. The inverse should be done when shutting down. Thats the easy (and safe) way to do it.

Matt

[theminor]

Thanks, Matt. The problem with this suggestion is that I can't start Mach without my controller on since there would be no power to the smoothstepper. I currently have my smoothstepper powered by an external 5V. I suppose I could change the smoothstepper to be powered by USB and then follow your procedure, but I still feel like this setup is dangerous because if Mach crashes or unexpectedly dies for some reason, my router will turn on unexpectedly.

What I need is an output that is normally low when mach is not running. It is currently normally high, except that it goes normally low when mach is running...

[keebler303]

I think the problem is that your output is pulled up by a resistor and then mach signals when the smoothstepper should pull it down. If you supply a pulldown resistor, it may fight the pullup already existing. I am not sure if the smoothstepper has a guaranteed logic state at turn on. You can easily change the logic in mach so that high is off and low is on. How does that output control your spindle? A relay, SSR, ??? ANother possibility would be to use a BOB with a charge pump so that mach would have to be running before it would output any signals.

Matt

[theminor]

I'm running a solid-state relay on it. Would it work to change my wiring as follows:

Run (+) 5 volts from my power supply to the (+) on the relay.
Take the output from the output pin on my BoB to the (-) on the relay.

So the relay will be getting (+) on both legs on the input side of the relay normally (when Mach is not running, and I'll set the output in Mach to be "Active Low"). When Mach gets an M3 or M4, it will set this pin low, which means the relay will have (-) on the (-) side and (+) on the (+) side.

Makes sense to me, but I wanted to be sure there was nothing wrong with the relay getting (+) and (+) when the spindle is off...

[ger21]

Power to the PC and SS should be separate from power to your spindle and drives.
That's the only truly safe way to make sure the spindle can never turn on "by itself".

[theminor]

Thanks, but they are on separate power supplies. I have a separate 5 volt supply for the smoothstepper and BoB (the bob takes 2 power supplies since one side is opto-isolated) and of course the drivers (I use g203vs) have their own higher-voltage power supply. All the grounds are separate.

The router isn't turning on "by itself" - only when Mach is not running (or when Mach tells it to turn on). It would only be unexpected if Mach crashed or something...

Anyone think my idea of running the (+) to my relay would work?

[nicad]

I have had the same issue, and yes I ended up getting a few reed relays to "invert" the default low output of my BOB.

I have a couple of C10 breakout boards, which have pull down resister banks on all the outputs so that when power is applied, with no data, all outputs go low. This sounds like it would be "safe" for most applications, until I connected things like the Hammond Designs spindle controller which is low active! And relay boards which are also low active. So they all enable when there is power and no Mach loaded to set the outputs high.

So, I applied a "fix" to one of the BOBs. I isolated the trace on the circuit board that connected the banks of resistors to ground (scratched it away) and soldered a jumper wire from the bank over to near the power plug, so I can connect them to either ground or Vcc (pulls up or pulls down). The C10 has a dedicated row of 4 outputs (14-17 I think?) and then a row of 8 selectable in or outputs. They each have their own bank of pull resisters. I did this for each row so I can select one bank to be low and one to be high, or both, etc..
I know its been a while for this thread, but I fought the same thing so perhaps this will help someone in the future. I am betting that most other BOBs could have the same mod done to them.

-Colin