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CMOS
Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA
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 06 Jun 2004 17:39 LCD cable length |
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Hi,
I want to know what is the maximum length of cable that I can use to connect an HD44780 based 16x1 LCD display to any microcontroller, say 89C51?
In one of my project, I need to place LCD on the front door of a small metal cabinet and to make sure that cabinet's door open completely, my cable length should be atleast 45 cms. Will this much length work without any problems? Same is the case with 4x4 Matrix keypad.
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shorty
Joined: 26 Feb 2002
Posts: 60
Location: Austria
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06 Jun 2004 22:21 Re: LCD cable length |
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hi
i have testet cable lengh up to 30 m with standard rs 232 cable (shielded)and it works fine
the value of the pull ups must be low (1k2)
shorty
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06 Jun 2004 22:21 Ads |
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CMOS
Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA
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07 Jun 2004 5:57 Re: LCD cable length |
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30m !! Thats great!!
Were your signals TTL compatible? i.e. 0-5V?
Right now I am using 4k7 pull-ups on 89C51 ports. That means it should run 45 cms wihtout any problems.
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simce
Joined: 09 Jan 2004
Posts: 195
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07 Jun 2004 8:35 Re: LCD cable length |
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| I've tested this kind of LCD with cable length of about 3m (TTL levels) and there were no problems. But take in mind to use shielded cable or flat cable but with twisted pairs. Every pair should be combination of ground/signal and put termination resistors on LCD side if you are only writinig to LCD (small resistance-0.5-1k and maybe small capacitors 2-3pF). You can use ferrite bead on end of the cable. Also reinitialize LCD from time to time (i mean full initialization). If you have problems lower the frequency of signals sent to LCD. I've not tested for longer cable, but everything can be possible.
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betanorm
Joined: 13 Aug 2001
Posts: 44
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07 Jun 2004 8:45 Re: LCD cable length |
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I think that the length of the cable depends on the pulse duration to send and receive data from LCD module, cable capacitance and output impedance of the MCU.
If you keep signal durations long enough to overcome the cable capacitance, then the output resistive component of impedance would be the limitation...
My experience which I spent days... ->On my first use of digital humidity and temperature sensor SHT-11 from Sensirion, it didn't give back ack signal. That means it didn't worked. Everything was OK, both the hardware and the software. Finally I realized that the cable impedance and length was the main problem. When it was shortened to an appropriate length, the sensor begin to give responses and worked very well.
Last edited by betanorm on 07 Jun 2004 14:18; edited 3 times in total |
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simce
Joined: 09 Jan 2004
Posts: 195
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07 Jun 2004 11:32 Re: LCD cable length |
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betanorm is right.
You must adjust the pulse duration regarding cable impendance (all resitive, inductive and capacitive componens are important).
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pico
Joined: 30 Sep 2001
Posts: 285
Helped: 6
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07 Jun 2004 14:47 LCD cable length |
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| TTL Level normally should not exceed 5 feet.
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Learn Kid
Joined: 24 Oct 2007
Posts: 1
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24 Oct 2007 3:07 Re: LCD cable length |
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Please Help!!
I had a problem with sending data from MCU through RS232 Data Cable (7x0.2mm) with 6 meter and 3.1 meter to LCD module with 4 data line mode, it seems that the signal receive at the LCD terminal crash especially the Enable bit, could anyone offer your kind helping hands! Thank you.
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pico
Joined: 30 Sep 2001
Posts: 285
Helped: 6
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24 Oct 2007 5:03 LCD cable length |
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| RS-232 max. cable lenth is 50 feet and max. speed is 20 kbps. and voltage is +- 12v to +- 15v
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