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lighting a 7 segment LED

Discussion in 'Microcontrollers, Programming and IoT' started by foTONICS, Nov 11, 2013.

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  1. foTONICS

    foTONICS

    332
    9
    Sep 30, 2011
    hi-jack away, I've gotten my answer


    Thanks everyone for all the help and insight. I've applied the corrections, given each segment it's own resistor and the display couldn't be brighter (even when the "8" is lit).
     
  2. dncky

    dncky

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    Nov 10, 2013
    Thorough, thanks. I bought a couple of these

    http://www.ebay.com/itm/18119947329...eName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

    I think the listing says 2.1 drop. I believe 20mA is standard so that's what I think Ill do.

    I have 2 digits so 14 segments. No multiplexing, Ill have enough pins I believe. Im going to spring for a 12v supply and Ill have a 5V rail for the circuitry.

    All Ive got to figure out is how Im going to hook up the N channel mostfet
     
  3. gorgon

    gorgon

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    23
    Jun 6, 2011

    The Vf drop depends on the colour. Normally 2.1V should be yellow or green. Red is around 1.7V and blue and white 3V +. 20mA for Ultra Bright could be more than enough, depending on what you want to do.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Have a look at Digikey's LED range sometime, sorted by colour. There's actually quite a lot of variation in forward voltage for a given colour, even within the "indicator" category.

    It's very straightforward.
    So:
    +12V to anode of segment.
    Cathode of segment to drain of N-channel MOSFET.
    Source of MOSFET to 0V rail (common ground of +5V and +12V rails).
    Gate of MOSFET driven from microcontroller I/O pin.
    Pulldown resistor from gate to source of MOSFET (to prevent floating MOSFET gate during reset etc) - 10k or 100k is fine.
    It's also common to insert a low-value resistor between the microcontroller output and the MOSFET gate - something like 47 ohms - because of the MOSFET's gate-source capacitance, but this is probably not important with a small MOSFET that's not being switched constantly.

    When firmware drives the pin high, the MOSFET conducts and illuminates the segment.

    Traditional MOSFETs BS170 and 2N7000 will work. 2N7000 is slightly better; it has a guaranteed RDSon of about five ohms at Vgs=4.5V.

    A much better option is the Zetex / Diodes Inc ZVN4206: http://www.digikey.com/product-detail/en/ZVN4206AV/ZVN4206AV-ND/190158
    This has a guaranteed RDSon of 1.5 ohms at Vgs=5V and 500 mA drain current.

    An even gruntier alternative is Vishay Siliconix IRLD110: http://www.digikey.com/product-detail/en/IRLD110PBF/IRLD110PBF-ND/812489 which is packaged in a 4-pin 0.3" DIP (optocoupler style).

    There are other MOSFETs that have better specifications, including several (NTD4906N, NTD4963N and NTD4815N) from ON Semiconductor, but they have much higher gate capacitance and are a bit out-of-place, even though they are cheap.

    All the devices I've suggested here are through-hole (wire leaded). Most are TO-92 or E-line.
     
  5. dncky

    dncky

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    Nov 10, 2013
    Awesome. Parts on the way. Ready to experiment
     
  6. dncky

    dncky

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    Nov 10, 2013
    Got it. Everything works fine. Mosfet works perfectly. Now the only thing I worry about is the segments visibility in daylight. So excited. Will test tomorrow!
     
  7. gorgon

    gorgon

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    23
    Jun 6, 2011
    You can use optical filters to increase the contrast of the displays. This will also help in daylight viewing.
     
  8. ligo.george

    ligo.george

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    Feb 2, 2013
  9. Mark2019

    Mark2019

    14
    4
    Jul 7, 2019
    Yes thats 3/4 of the problem No schematics and no real appreciation for hardware I'm glad someone has spotted this

    First comes the hardware then you learn how to code
     
  10. hevans1944

    hevans1944 Hop - AC8NS

    4,195
    1,985
    Jun 21, 2012
    @Mark2019: No, first is learning how to read and observing this thread was started on November 11, 2013.

    @KrisBlueNZ sadly passed away in 2015. We miss him, but this thread is DEAD. It should have been closed by a moderator after November 27, 2013 when @ligo.george made the last relevant post, #28.

    I guess the new owners just can't be bothered right now with cleaning things up and taking out the trash. There are a lot of abandoned and/or dead threads that continue to pop up in the forum listings. You need to look at the posting dates before deciding to bump one those threads, something I also sometimes fail to do...:oops:
     
  11. Mark2019

    Mark2019

    14
    4
    Jul 7, 2019
    I'm sorry to here that KrisBlueNZ

    I guess this sounds about correct at present with an awful lot of these sites

    I am looking for sites that do really want to change this entire process and reverse some of the quality Equally responses as well with a far more interested approach over all and with some more meaning full team on a joint profit sharing basis that would enhance peoples lives but trying to find people like this at present is very hard job

    Hence I came across this site and saw the adverts requesting for persons to write articles for them

    As yet no real answers or negotiations which is a little disappointing having left messages to the advert to two different moderators thus far

    Thank you for being kind enough to let me know anyway

    Once again my condolences to your team

    Lets hope this will be somewhat more successful than some sites have been thus far

    Have a good weekend and wish you all well
     
    Last edited: Jul 20, 2019
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,689
    Jan 21, 2010
    Generally speaking, threads are not closed unless there is some reason to do so.

    We have had people come back to their original thread after several years (not often, but it happens)
     
    davenn and hevans1944 like this.
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