Thread: Will a 40x4 character LCD (Arby) work over a 50 foot parallel cable?

I'm gonna stick my neck out and say no (probably) with the current crop of drivers. With long parallel cables, an effect known as bit slew is experienced. This is where the bits of data travelling along the wires travel at different speeds (due to manufacturing tolerances on the wirese). Higher quality cables have less of a problem with this. Serial has no problem with this since all the bits just follow each other down the single wire (line driver capability/source impedance is then the issue, which dictates cable length, along with cable impedance/terminated transmission lines).

Generally the drivers are tuned to be fast (certainly true of the drivers I've written). This means speeding up the data timing to maximise throughput). I have no doubt that it could be made to work by dropping the speeds. Data is latched into a 44780 by a single latch signal, and so by setting up the data and waiting a while for it to settle before latching the data, a long distance connection could be made to work.

Then you have interference and voltage drop along the wire, although I wouldn't expect this to be a problem with a decent shielded cable.


Rob

Just get the cable, then cut it to the length you need, and re solder it back together. Then you'd have a ton of extra wire for any thing you need (low voltage though).

if youre wiring it directly to the lcd, that makes it easier, because you only need to resolder about 16 lines, not all 25.

I have soldered a ~ 5m cable to 20x4 HD44780 Display yersterday night . Doesnt work - soldering is correct current/contrast also - but te display doesnt display anything

- so am I right by thinking that ~5m is too long ??



Felix

I have tested and a 25' will work, never tried a 50'.

Originally posted by felix99
I have soldered a ~ 5m cable to 20x4 HD44780 Display yersterday night . Doesnt work - soldering is correct current/contrast also - but te display doesnt display anything

- so am I right by thinking that ~5m is too long ??



Felix

I think it also depends on the parallel port off the board..

I have a 40x4 wired to 5.4m and it works perfect on one board , but not on another board...
Just play with it.. to see if it works

Greetz,

I agree with Raas, some mobo's work differently to others. I had a 6m parallel cable running slugishly on a P133, but on another board it runs ecp and everything!

You can use a PIC to convert it from serial to parallel and drive it serial for a couple of bucks and a bit of veroboard. No-one replied to my post on this earlier, so I gather you guys don't like soldering irons.... If someone wrote a winamp plugin for it however....

Bj

Raas & BJ you are right - just tried the lcd on my girlfriends computer and it works !! on mine - so next weekend when i get LPT adaptor for AT Mobo I'hope it would work on my carputer.

Its very curious I think - could it have something to do with the ECP EPP etc modes I can choose for LPT port in bios ?
What does this mean and whats the best mode for LCD's ??


Tnx

Felix