reprapdiscount LCD display

I'm pretty sure that all of the robo supplied versions of the firmware are set to work with the XXL.

 

yes.

 

These LCD controllers have rugged HC4050 level translators/buffers for the SD Card on the SPI bus.

I really can't see why you couldn't even run the SPI signals over a rusty bit of barbed wire for 90cm.

 

There must be something that you're missing in the analysis. I've heard repeatedly that they fail when you extend them and they're marked with a warning label saying not to go beyond 30cm.
Maybe there are some answers on the reprap forum?

 

LCD Display and SD Card are separate functions on these controllers. SD Card uses SPI. LCD does not.

Looks like I will have to find some rusty barbed wire to try it.

 

I searched the forums for any reason why extending the LCD controllers does not work and could not find anything plausible.

As I have mentioned before, the SD Card uses Arduino SPI which is a robust bus protocol. The LCD itself just uses 5v logic levels and is very low speed.

So I made some one meter long flat IDC cables to try it. As expected the LCD and SD Card functions work just fine over this one meter distance. I can upload files to the SD card, run prints from the SD Card and all the LCD functions work correctly.

Only explanations I can think of why others have failed are:

• The longer IDC cables have not been made correctly - it is very easy to get the cables reversed or leave conductors not connected.

• The gcode files uploaded to the SD Card (eg from Repetier) are not identical to the gcode files on the PC. Repetier removes comments and drops some unecessary decimal points when the files are uploaded. It's possible that someone has compared the files and thought there was a problem - when there was not.

 

Why???

I made the cables using standard flat cable and 10 pin IDC connectors. Otherwise you can buy cables on ebay

 

Can you give me a reference to what you have read.


Everything I had learned as an Elec Eng and had experienced with Arduino, SPI and logic circuits convinced me it would work over at least this distance.

But I could see the myth was so strong that some proof was required. Hence I used one meter of flat cable (which would normally be far longer than needed) to demonstrate conclusively that it works.

It will not make any difference which Reprap discount controller you use. They all use basically the same technology and circuit design. However I will test the other (non graphics) one I have as well. Viki could be another story - I just have not looked at its design.


I've run about 7 hours from the SD Card over the one meter cables so far. Unfortunately the myth is very strong and I am sure all manner of problems will be blamed on LCD cables longer than 30cm. I don't need one meter but will keep using the cables for at least another month as I am sure I won't see any problems.

BTW : I hope no one thinks I am having a go at anyone for calling this a myth. I think all of us have seen situations where if something is repeated often enough by enough people, it is taken as a fact.

 

I have tested the older Reprap Smart Controller with one meter cables and it works. But some care needs to be taken with this older LCD design. The LCD part is no problem, but the SD Card reliability can be tricky. Reason is....

First - The design of the old "Smart LCD" controller is functionally identical to the later "Full Graphics LCD". Cable pins are the same, buffering chip is the same, SD Card circuit is the same. BUT the designer has completely ignored the need for filtering capacitors on the 3.3v power regulator and bypass filtering on the buffer chip. So the whole Smart LCD controller design is very noisy. All these design problems have been fixed on the later Full Graphics LCD controller.

And - The cable connector orientation on the Smart v Full Graphics LCD is reversed. So you cannot use the same Ramps board connector for both.

The "Smart LCD" controller can be extended to one meter but the "noisy" design needs to be taken into account. I found that just taping the two flat cables together was enough to dampen the noise.

Overall recommendation is forget the older "Smart" LCD controller with the less than smart design. Far better choice is the "Full Graphics LCD Controller".





Note : Reversed connectors

 

Ziggy thanks for the test and analysis.

I really don't think this falls into the category of myth though. The manufacturer, who is also the designer in this case, places a label on the package that says not to extend cable beyond 25-30cm. The explanation around change in electronics between the smart controller and full graphics makes sense. Perhaps they just made up the stickers and never changed the text with the new design?