How to extend an inverters lcd display wiring?

Discussion in 'The Projects Forum' started by ceefna, May 31, 2016.

  1. ceefna

    Thread Starter Member

    Feb 21, 2012
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    Hi I have a 2500w pure sine wave inverter in my motorhome, the inverter is located in the rear storage next to the leisure batteries and i want to move the small lcd display that shows voltage/amps/temp etc into the living space (approx 6 meters away) so i can monitor the output and temp without going outside the motorhome to access the inverer.
    I have made a 7pin extension wire and the display works perfectally for a few seconds then it stays illuminated but the display goes blank.
    I have tried normal wiring and twisted pair network cable but its still the same. any ideas if what i am trying is possible or should i give up?

    Just to add my electronics knowledge is basic at best! so please keep any advice simple.

    Thanks for your time
    Ceefna
     
  2. ceefna

    Thread Starter Member

    Feb 21, 2012
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    IMG_2406.JPG IMG_2407.JPG
     
  3. ceefna

    Thread Starter Member

    Feb 21, 2012
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  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    If just getting longer wires is out of the question, as it might be, consider wireless communication. There are some off the shelf devices that will take a serial data input (which you have) , transmit it, and give the same serial data out. I personally have used the XBee devices.

    Now for the bad news. That will get you the data, but you will also have to supply the other 4 pins (i.e., 7 pins minus pins 1,2,and 3) :
    upload_2016-5-31_17-45-1.png

    So you have /WR (aka read write) , and /CS (aka chip select) that are used to control the display. You will need a microcontroller at the receiving end to give you something like you are used to seeing. You can probably do without /WR, but not a /CS. The two LED pins are not a problem to supply locally.

    Have you tried longer wires like internet cable?

    John
     
  5. ceefna

    Thread Starter Member

    Feb 21, 2012
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    Thanks for the reply
    I have tried normal house alarm wiring and also cat 5 patch cable both with the same results.
    It does say in the spec on the eBay page that the lcd cable needs to be shielded. If I was to use the twisted pair Ethernet cable which pins should be paired up to give me my best shot or does it not matter?
    Also will dividing the power and data into two cables help?
    Thanks again for your input

    Ceefna
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
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    1) Buy a car reverse view camera setup- point the camera at the display. (easy - cheap - fast)

    2) Convert the signals to differential voltage transmission to work over the distance using twisted pairs.
    You need a differential driver on each signal line, and a differential receiver to convert back to the single ended signal the display needs at the other end. (slow - painful)
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The eBay listing describes the LCD display as being based on the SG1621B controller chip. That is apparently similar to the very common Hitachi HD44780 chip that is used in most 16X2 LCD displays. You might search on long extensions for those (i.e., 1602 displays). If you find something, it would surely be applicable to your situation.

    As Sensacell pointed out, your data line is not a differential signal. Twisted pair might help, but the emphasis in the eBay listing is for shielding from the electrical noise of the inverter. What happened when you tried the cat5 cable? Did you see anything or was the gibberish? Unfortunately, I have no experience with long-distance wired connections with this type of signal.

    Here are a couple of links that discuss 1-wire serial communications that might be helpful:
    https://www.maximintegrated.com/en/app-notes/index.mvp/id/148
    https://en.wikipedia.org/wiki/1-Wire

    Can you adjust the baud rate? If so, then decrease it by one step or more.

    John
     
  8. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The problem is probably due to the capacitance of the cable skewing the clock and data signals. You could try adding some simple repeaters (powered from the 5V that is already on the line) along the cable based on inexpensive 74AC14 hex schmitt inverters. Build each repeater on a small piece of stripboard and be sure to add small (0.1 - 1uF) local decoupling capacitors across the power lines for each repeater and also at the LCD end.

    http://www.mouser.com/ds/2/405/sn74ac14-444244.pdf

    There are six inverters in a package and you have 3 control lines so use a pair of inverters in series for each line. I'm assuming that data is one-way and the LCD is never read by the controller, I wouldn't expect it to be.
     
  9. Sensacell

    Well-Known Member

    Jun 19, 2012
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    This 'might' work ok- but if you are going to all that trouble- why not make SURE it will work by going full differential? It's only slightly more effort than inserting buffers.

    Then you don't need to worry about the ground jumping around, screwing up the logic thresholds.

    Differential is really robust over long cables, single-ended is a crap shoot.
     
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    It might work if you used un-shielded twisted pair CAT5 cable, making each signal a pair with a grounded lead.
    This scheme should have less capacitance relative to shielded cables.

    Maybe a second CAT5 for the Vcc and GND, and LED lines. Add extra capacitors to the power at the display end...

    That would be your simplest lucky strike- just... barely... making... it... 6 ... meters...
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi @ceefna,

    I fear you have been scared off by what you thought was a simple problem. A wild thought occurred to me on a long drive today. There is a chance that the serial data from that one line (pin 3) will be identical to the serial data sent to a regular serial 2X16 display. Parallax makes one (used to be sold at Radio Shack) and I am sure there are others (eBay). The Parallax one is relatively expensive. I don't consider the chance of success is very high, but it is not nil. If you can borrow such a display (it will have only 3 wires) try connecting the data wire to the data line and the V+ and Gnd wires to the respective power lines. See what happens. You may need to set the baud on the display. Try different bauds.

    The result may not look the same, but it may be intelligible.

    John
     
  12. ceefna

    Thread Starter Member

    Feb 21, 2012
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    Hi all thanks for your replies
    I have bee slightly scared but not totally put off!
    The display does work perfectly for a few seconds after switching the inverter on but either displays some random voltage and temp values goes blank or just goes blank but stays illuminated.
    Then it needs the inverter power off/on to display again.
    I am going to try using 2 cat5 cables one for data and one for power as suggested. It seems the way I have it wired at the moment I have pins 1&2/3&4 etc as twisted pairs. This means both my data pins are twisted together and I believe this is a big no no?
    I will ground each twisted data to ground and see what happens.
    Thanks for your input and will let you know if it works.
    Ceefna
     
  13. ceefna

    Thread Starter Member

    Feb 21, 2012
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    It works!!!!!!!!!!!!!
    I just swapped the twisted pairs for the data connections and ran the power on a seperate cable
    thanks for all your help

    Ceefna IMG_2416.JPG
     
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