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  1. #1
    Hi all

    I am trying to implement EddyCurrent's flasher circuit but am having issues with it. He uses a System1 V2 BOB and I am using a PMDX 126. In a PM EC explained he used the BD679 as follows:

    Pin14 from the BOB connects to the base of the BD679 via a 2.2k ohm resistor. The emitter is connected to 24v negative and the collector is connected to one side of a "lamp". The other side of the lamp is connected to 24v positive. The flashing is controlled by a brain supplied by EC.

    Now, I built this little circuit using a 24v LED as the lamp and it just glows in a low light and does not flash at all. I have PM'd EC asking what his "lamp" was but at this point he has not replied. I am now suspecting the "lamp" may be just that, a light bulb and not an LED. My LED is a true 24v LED in a pushbutton size package.

    Can anyone see what I might need to use the 24V LED in a circuit such as this AND have it flash as required from the brain?

    Any help would be appreciated.

    Last edited by ozspeedway; 10-07-2014 at 12:41 PM. Reason: spelling & grammer

  2. #2
    Sounds like it should work provided the base of the transistor is being driven high by the BOB (break out board ? Sorry, I'm new to this site having just purchased a mill to convert). The BD679 is a darlington device so won't need much base current to switch it on.

    It sounds like the transistor is missing its base drive - perhaps you need to configure something in your CNC software to make Pin 14 a suitable output ?



  3. #3
    Thanks Robin

    The problem is it *is* working in as much as the led is on all the time instead of off until flashed. I checked Mach and the output flashes in the diagnostics screen. I'll reconfigure the circuit again (have tried 4 transistors so far) with one of the last 10 transistors I have. I'll also get a 24v lamp to test it if I can find one today.


  4. #4
    Well it is definitely something I am doing, EC just replied to my PM and he is using the same style LED lamp as I am. I'll check I have everything the right way round and report back.

  5. #5
    If you're sure that you pave the pins connected correctly (see attached) then the next suggestion, assuming you have a multimeter, is to measure the voltage between the base and emitter of the BD679 to check what the BOB is sending. Name:  BD679_Pinout.gif
Views: 977
Size:  2.1 KB


  6. #6
    Hi Robin

    Just ducked down and checked the pinout and all as per required. Measured the voltage as suggested and got 0.04v yet the LED is glowing and not flashing. Just for kicks I measured between the base and the collector and got 12.67v. The brain was active and "flashing" yet it made no difference to the LED. If I disconnect the parallel cable the LED goes out even with power still applied to the BOB. I have tested this with 2 different BOB's, a PMDX 122 and an MB06-v2 from homann designs in Aus, both show the same behaviour. The LED stays lit even when pin 14 (assigned to OUTPUT1) is disabled. Got me stumped at this point.


  7. #7

    This is the drawing for mine, just checked it at the machine itself.
    Click image for larger version. 

Name:	circuit.jpg 
Views:	195 
Size:	19.3 KB 
ID:	12760
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  8. #8
    Thanks Eddy, looks just like what my version is. I now suspect our differences come from you using an ethernet smoothstepper and me using a parallel port. I have a strong suspicion that the PC is filtering some voltage via the P/port that the BD679 is seeing. I can confirm that by taking the p/port cable off the BOB and the LED goes out. Of course I can't then test Pin 14 out. However, an ESS is in my immediate future (next week some time) so I will see if my gut feeling is correct.


  9. #9
    I've just had a look at the PMDX manual, it looks like you should be using pin 14 or 16 of J8 and JP3 should be set to 'outputs enabled', that's what it looks like after a quick read anyway. The outputs have an LED so it should be easy to see the state of your chosen output. I can't see the ESS making any difference so I would disconnect the flasher and concentrate on getting your bob output to go on and off from the software and not using the Brain function. When you get the output to operate correctly then connect the flasher and it should go on and off with the output. Now bring the Brain into operation and provided the logic is okay the flasher should operate.
    It may be that the lamp is dim because it's being switched at high speed, try a multimeter with frequency range across the lamp.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  10. #10
    What's the 'brain' function then ? Forgive what may be a dumb question, as I said I'm new to CNC...

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