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  1. #11
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 5 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,837. Received thanks 192 times, giving thanks to others 5 times.
    8901234567
    Last edited by m_c; 20-05-2014 at 10:40 PM.

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  3. #12
    dudz's Avatar
    Lives in Bretagne, France. Last Activity: 20-05-2017 Has been a member for 4-5 years. Has a total post count of 256. Received thanks 1 times, giving thanks to others 50 times.
    So after the resistor is in place from the output wire to the +5v, if the switched wire goes to Gnd, does that mean the 5v will go to ground also ? (sorry for my lack of understanding)
    Last edited by dudz; 13-06-2013 at 02:56 PM.
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  4. #13
    dudz's Avatar
    Lives in Bretagne, France. Last Activity: 20-05-2017 Has been a member for 4-5 years. Has a total post count of 256. Received thanks 1 times, giving thanks to others 50 times.
    Ok, I understand now. I wasnt sure if the resistor was enough to stop the voltage going to Gnd and damaging something.
    3 axis CNC/router / Alu profile frame....25mm Alu Cutting bed X=500mm Y=300mm Z=110mm.....Supported 25mm X rails ....Supported 20mm Y rails....Supported 20mm Z rails.....2.2kw Chinese WC spindle......"USB Breakout Board Interface 200KHz"....M542 Drivers..SY60STH86-3008BF Motors...running....Mach3 / Cambam / Emachineshop.

  5. #14
    m_c's Avatar
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    abcdefghij
    Last edited by m_c; 20-05-2014 at 10:41 PM.

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  7. #15
    Quote Originally Posted by m_c View Post
    The resistor is sized so that when the output switches to ground, there's only a few milliamps flowing through it.

    I just ran the figures, and with a 4k7 resistor connecting 5V to ground, it's only allowing slightly over 1mA through, so you could use a lower resistance value.
    Using a standard 1/8W resistor, you could go as low as 200ohm before resistor overheating becomes a problem. I'd personally opt for something in the 1-2K range, but it's not critical.
    Resistor overheating isn't the limiting factor. With 200 ohms you'd have 5/200=25mA. The parallel port can (apparently) only source/sink about 14mA, hence to avoid damaging the port if connecting directly I'd use something higher. So I'd agree to sticking with at least 1k just to be on the safe side.
    Last edited by Jonathan; 13-06-2013 at 11:45 PM. Reason: Grammar
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  9. #16
    m_c's Avatar
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    xyz123abc.
    Last edited by m_c; 20-05-2014 at 10:42 PM.

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  11. #17
    dudz's Avatar
    Lives in Bretagne, France. Last Activity: 20-05-2017 Has been a member for 4-5 years. Has a total post count of 256. Received thanks 1 times, giving thanks to others 50 times.
    Some specs from the BOB Manual

    Click image for larger version. 

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    The Sensors are NPN.
    Last edited by dudz; 14-06-2013 at 08:53 AM.
    3 axis CNC/router / Alu profile frame....25mm Alu Cutting bed X=500mm Y=300mm Z=110mm.....Supported 25mm X rails ....Supported 20mm Y rails....Supported 20mm Z rails.....2.2kw Chinese WC spindle......"USB Breakout Board Interface 200KHz"....M542 Drivers..SY60STH86-3008BF Motors...running....Mach3 / Cambam / Emachineshop.

  12. #18
    m_c's Avatar
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    mycncuksucks
    Last edited by m_c; 20-05-2014 at 10:42 PM.

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  14. Quote Originally Posted by m_c View Post
    Looking at that, the inputs require 7mA at 5V, which somewhat complicates things if using a NPN sensor, as the inputs obvisouly have resistors installed to drive the Optos.

    I've got to head to work now, but if nobody has replied by later, I'll figure out some values to use the sensors you have.
    assuming 1.2v forward voltage on the opto means that the existing series resistor is (5 - 1.2)/.007 =542, so probably 560R. the suggested series resistors of 1,5k for 12v and 3k for 24v give currents of 6.9mA and 6.4mA respectively.

    dropping the 'on' current to 5mA will need a pull up resistor of 220R and the 'off' current through the 220R would be (5-.4)/220=21mA and 0.1W dissipation, needing a 0.25W resistor. I guess 5mA through the opto will be ok and not have noise immunity issues.

    It would be better to use a higher supply rail, e.g. 12 or 24v and use the suggested 1k5 or 3k resistors 'off' current/power being 7.7mA/0.1W or 7.9mA/0.2W respectively.

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  16. #20
    dudz's Avatar
    Lives in Bretagne, France. Last Activity: 20-05-2017 Has been a member for 4-5 years. Has a total post count of 256. Received thanks 1 times, giving thanks to others 50 times.
    Ok... I have a spare PC PSU. 12V (Model LC B200SFX)

    If I use this to power the sensor, I connect the PSU -0V to the sensor and to the Gnd terminal on the BOB as shown "right ?" plus the +12V to the sensor input. Using the 1K5 to limit the input to the BOB.
    Do I still need a pull up resistor ?..... Its getting a bit confusing for me.
    Last edited by dudz; 14-06-2013 at 05:41 PM.
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