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LCD and digipot cable length?

 
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Will Reeve
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LCD and digipot cable length?
PostPosted: Fri Jan 17, 2003 3:48 pm     Reply with quote

Hi all,
I have a PIC based project using a LCD screen (usual 4bit interface) and also a digital pot as an input device. I need to run the LCD and 'pot about 1m from the PIC, is this recommended? It all works OK but want it to keep working in possible noisy automotive environments. I was thinking about making a spi connection with another smaller PIC at the LCD end but then again spi is probably just as likely to be susceptible to interference? Any thoughts would be much appreciated.

Will
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R.J.Hamlett
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Re: LCD and digipot cable length?
PostPosted: Fri Jan 17, 2003 3:59 pm     Reply with quote

:=Hi all,
:=I have a PIC based project using a LCD screen (usual 4bit interface) and also a digital pot as an input device. I need to run the LCD and 'pot about 1m from the PIC, is this recommended? It all works OK but want it to keep working in possible noisy automotive environments. I was thinking about making a spi connection with another smaller PIC at the LCD end but then again spi is probably just as likely to be susceptible to interference? Any thoughts would be much appreciated.
:=

I have to admit, that I have found the inputs to many of these LCD displays to be particularly susceptible to noise. When running even quite short lengths adjacent to relatively large electrical fields, termination, shielding, and supression has become necessary. Your 'balancing act', will depend on the relative cost of providing good shielding on the cable, against the extra processor. If you are using a second processor for this type of application, consider using RS485, and a twisted pair cable.
However that having been said, unless the enviroment is ridiculous, 1m should be comfortably achievable, with a bit of care on the cableing and layout. Normal TTL signals can be run several times this length, by generally being a bit careful in the design - work out how both the signals and the ground are going to be handled. Consider using a twisted pair cable, with alternate grounds. Look at signal termination, and protection on the inputs.

Best Wishes
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oscar
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Re: LCD and digipot cable length?
PostPosted: Fri Jan 17, 2003 4:22 pm     Reply with quote

:=Hi all,
:=I have a PIC based project using a LCD screen (usual 4bit interface) and also a digital pot as an input device. I need to run the LCD and 'pot about 1m from the PIC, is this recommended? It all works OK but want it to keep working in possible noisy automotive environments. I was thinking about making a spi connection with another smaller PIC at the LCD end but then again spi is probably just as likely to be susceptible to interference? Any thoughts would be much appreciated.
:=
:=Will

Will,

1 meter in an automotive environment is like 10 meters under desks full of PC's and lab equipment.

I recommend you get yourself a CAN transceiver chip TJA1050 on either end of this cable and connect it to a CAN compatible micro. This means that your current micro has to be a CAN compatible micro. This does sound like a lot of work but wait until you have to design the power supply for this circuit (using 12V from car I assume?) you'll really be worried then.

Take it from an automotive electrical engineer, noise in a vehicle is a pain in the arse.

Good luck,
O
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Re: LCD and digipot cable length?
PostPosted: Fri Jan 17, 2003 4:43 pm     Reply with quote

:=Hi all,
:=I have a PIC based project using a LCD screen (usual 4bit interface) and also a digital pot as an input device. I need to run the LCD and 'pot about 1m from the PIC, is this recommended? It all works OK but want it to keep working in possible noisy automotive environments. I was thinking about making a spi connection with another smaller PIC at the LCD end but then again spi is probably just as likely to be susceptible to interference? Any thoughts would be much appreciated.
------------------------------------------------------------
Possibly change to an LCD with an RS-232 interface.
<a href="http://www.seetron.com/slcds.htm" TARGET="_blank">http://www.seetron.com/slcds.htm</a>
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Original Post ID: 10771
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