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Offline GPDC

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Logic Probe
« on: January 13, 2008, 10:49:50 PM »
  This may be a little off topic, if it is , ignore me & I'll go away
Long story short: I've aquired a BK logic probe (with pulse sensing) to help me troubleshoot start up problems with a HobbyCNC 4AUPC R2 board...this probe has black & red power leads, and then the actual probe tip....must I get onto my computers' 5 vdc logic power supply to use this device to "see" the pulse train @ the respective LPT1 pin?....I figure I need this to determine the pulse train to the board is valid, the Dir hi or lo I can see using a VOM between Pin 25 (gnd) & the respective pin I've got set  for that in Mach....two days of silence over @ the hobby forum tells me nobody's got any info for me, but maybe oneof you wizzards amongst the guru's here can give me a little guidence?...I'd sure be appreciative!.....thanks,GPDC

Offline Hood

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Re: Logic Probe
« Reply #1 on: January 14, 2008, 01:16:42 AM »
Just did a search for the probe as I have never heard of them before, anyway if you dont have the manual you will get it here http://www.bkprecision.com/manual/DP21_manua.PDF  That is presuming its the DP21 model.
 A quick squint through the manaul shows you connect the red and black to the 5V supply of your computer and then just probe the step pin to get your pulse.

Incidentally you could sort of use a Volmeter for measuring that you are getting a pulse, if you put a meter between your step pin and ground and have it on mV range you would see a voltage when jogging one way and 0v the other, the faster you jogged the higher the voltage you would see. Its not perfect as you are not actually seeing much other than you are getting some output. A scope or probe like you have is a much better solution.
Hood
 

Offline GPDC

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Re: Logic Probe
« Reply #2 on: January 14, 2008, 08:48:52 AM »
Hood,
  I thank you for the info.....you've been kind enough to give me direction before...thank you, as for using the probe, it is a DP21 and the instruction sheet is a little vague on what PS it uses...now I know....I was trying to NOT open my computer case!.....fwiw...I did do the VOM test as you suggested & got those results, as you said I would.
                       Thanks, George P.

Offline Hood

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Re: Logic Probe
« Reply #3 on: January 15, 2008, 03:01:39 AM »
George
 You dont really need to go inside your computer to get its supply, you could hack up a USB cable to get the voltage from it.
Hood

Offline Hood

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Re: Logic Probe
« Reply #4 on: January 15, 2008, 03:05:49 AM »
In fact you probably dont even need to use the computers supply voltage, you could use any 5 volt DC supply but you would probaby need to link the 0v of the supply and the computer (a ground pin on the PP) so that your probe was referencing a common ground.
Hood

Offline GPDC

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Re: Logic Probe
« Reply #5 on: January 15, 2008, 08:26:01 AM »
  Hood,
Ah ha!.....thats a great idea, especially in view of the fact I took the side cases off my desktop computer yesterday & completely chickened out on even trying to tap the logic supply voltage.....waaayyyy to much stuff for this kid!
  But I did set a vom to millivolt & lo & behold I got an indication of a pulse train @ the respective ports in time with my key presses.
  Today, just for kicks I'll do exactly what you've suggested, just to see what the probe shows.
  This particular board (the 4AUPC) is waiting for replacement components & so is the new PRO board...missing mosfet, so I'm @ a standstill....yesterday I did the physical stuff for the (3) homing switches, but other than that, the machines' ready to go....it dosen't look as good or have all the operator interface stuff the first machine I put together (for a customer...there are pics of it w/my name attached posted), but then it dosen't need to....I'll be showing it soon....thanks again for your help.
                                    George P.

Offline Hood

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Re: Logic Probe
« Reply #6 on: January 15, 2008, 10:13:33 AM »
No problem George but for future reference its easy enough to get the 5v from the internals of the PC, a rough way (my usual ;) ) is just to shove wires into the molex connectors that go to such devices as HDD, CDROM etc, the Red Wire is 5v and the Yellow is 12v, you can use any of the Black wires in the molex as they are all tied to the same ground back in the PSU. Incidentally if you are needing a 7V supply you can connect between your Red and Yellow wires and you will get it, this is often handy for quietening down noisy case fans, run them on 7V and they go slower and are less noisy :)

Hood

Offline GPDC

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Re: Logic Probe
« Reply #7 on: January 15, 2008, 10:39:40 AM »
  Hood,
    What caught my eye quickly inside my PC case was the different voltages as marked on the PSU (AN ATX 350):  +3.3V....+5V...,+12V....-5V....-12V & +5 Vsb....what do you suppose that +3.3V is there for?.....looks like it's got 28A behind it!....that's light welding power!....I just now saw the pulses using the BK i9n time with my keystrokes & that makes for a really happy me!...many thanks for you continued info!....George P.

Offline Hood

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Re: Logic Probe
« Reply #8 on: January 15, 2008, 11:24:25 AM »
The 3.3v is used by the mobo for lots of things, in fact I think most of the mobo runs on 3.3V, its been a while since I was into overclocking and such but I know if you had a weak 3.3V rail in your PSU you would run into problems when overclocking. In fact the most important feature of the PSU from an overclockers perspective was the combined output of the 3.3 and 5v rail, even better if you had a good PSU that had seperate rails for each voltage. Whether this is still the same with newer mobos I am not sure.
 The Molex connectors that go to the IDE devices  just have 5 and 12V.
Hood

Offline Perfo

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Re: Logic Probe
« Reply #9 on: August 21, 2008, 02:36:51 PM »
I find logic probes very handy when setting stuff up. On another thread I've asked if anyone else would find one built on as a plug in to Mach 3 would be handy though I haven't had much response so far. Leeds3 is assisting me in looking in to the possibility of making a plug in that will have a logic probe screen on Mach 3.  I've made the probe and it works ok and for a very low cost.