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  • Author Author: phoenixcomm
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QUESTION: I think the sky fell on me. I need some help please. The tail of too, too many wires.

phoenixcomm

Ok I have been working with the NAV Computer Display Panel, for a while now an I run up to this wall. OK, this beast as there are 4 sixteen-segment alphanumeric displays and another 13 seven-segment displays, DISCLAIMER THEY ARE NOT LEDS THERE INCANDESCENT! They run at 4 vdc @ 15ma. per segment.

First, this is a whole lot of wires drivers, cussing, etc. Second, they run off the 5vdc supply. There are 4 sixteen alphanumeric displays (that is 64 wires), plus 13 more seven-segment displays that is another 91 wires and there are 4 decimal points (4 more wires, are driven via the GPIO on an Arduino.). When I first got them years ago I thought that I could run them with a MAX part but it only supports LEDs and it uses a technique called 'Charlieplexing'. 'To make this easier you can drive the 4 alphanumeric displays on one bus but then you need 2-bits to act as selectors these can be driven via an I2C 16-bit port IC. The 2-bits are driven via the GPIO on an Arduino. Now you have left, the 13 seven-segment displays.. 

Here is the caveat, the refresh rate of the Human Eye. 

Any Ideas please post a response. 

  • in reply to shabaz

      yes, but the two PCxxxx parts do not have on board decoders! so that more work for the CPU.  I will prototype some of the 7 segs with alphanumeric displays like two of each before I comment I will most likely need to have the boards made (maybe 3) as I don't know what type of wire nightmare I'm in for!.  

    Doing it this way I don't have to refresh the displays!! driving the alpha parts will require software maybe just a look-up table. 

  • in reply to phoenixcomm

    Hi Cris,

    That's a bit more circuitry regarding the LED driving, but if it's cheaper, then using CD4511 seems a very good idea. I didn't realize that part was still available, but I see it in stock at some distributors. It looks a great option.

  • in reply to beacon_dave

     ,    sad to say but this will not work as there are too many dives  13 7 seg, 4 16 segs, and 4 decimals and these I2C parts aren't cheap! 

    ---------------------------Inside the control unit ---------------------------

    just for the drives I am thinking of 4v DC-DC converters with a zener across the load set to 4.5 volts. I am looking into NPN Transistors wired to the ground and the segment between the Vs 4v and the collector. for the 7 segs I will most likely use CD4511 (13) addressing would be (2) SN74LS138  to handle the 16 bit are handled by (4) PCF8575 latches and the addressing is via (1) SN74LS138 total chip count = 20.

    now the PCF875 is I2C so that's 2 wires  (no decoding)

    decoding 7 seg is 4 wires for decoding 

    BCD for the 7 seq is 4 wires

     total wires that I have to worry about = 10

    ops I don't want to forget about power: (1) 5v & (3x) 4 volts and (1) ground  = 5 more  4v power is split into 3 (2 for the 7 segs & one for 16 segs)

    I forgot the(4)  decimals, Thinking hey I still fit onto a db25!!

    ---------------------------------- LRU ------------------ 

    Plus the switches bcd thumbwheel switches may 8 wires

    Plus 2 rotary switches 6 pole and 7 pole = 14

    plus debounce for all the switches 

    plus (2) SN74LS148 encoders which feed a PCF875

    This gives me a wire count for the LRU = 22 + 1 ground and 1 power = 24 hey I still fit onto a db25!!

    ------------------------------------------------

    BTW the only thing I am missing is the PWM drive Unamused

    I think this is better than 200+ wires 

    If I keep the LRU in the right side of the cockpit and use shield CAT6 cable I could go  1meter plus.. I have to test it and find out. 

  • in reply to shabaz

    There is also the PCA9635 which looks like the 16 output version of the PCA9634

    image

    https://www.nxp.com/docs/en/data-sheet/PCA9635.pdf

  • in reply to beacon_dave

    I've not looked in detail but at first glance they look very similar, and should be suitable for incandescents. Halves the chip count as you say! The MCP chip might be pushing it in terms of output current (it doesn't seem to be stated apart from the Absolute Max ratings but I may have missed it, am in a rush : (

    image