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Topic: IDE ribbon cable to link TFT display to it's adapter shield: bad idea? (Read 1 time) previous topic - next topic

guix

Hello,

I have Sainsmart's 3.2 TFT and the TFT Mega shield, sitting on top of my Arduino Mega.

Because I want the display to be ~15cm away from the Arduino, I buyed an IDE male-female, 40 wires ribbon cable.I believe it is 28AWG wires so I though it would work but...

It doesn't work, the backlight isn't bright like when plugged directly on the shield, instead it is very very low, I would say 5-10% of the normal light... What is the problem?

Did I just waste my money because an IDE cable can't handle the 5V required by the display (3.3V required by the backlight) ? I measured resistance between the 2 ends of some wires, multimeter show ~0.8 Ohms for each.

liudr

Could be good, could be bad. Are you sure you have 40 wire or 80 wire?

http://liudr.wordpress.com/2011/06/25/ide-harddrive-cables/

guix

Yes it's 40 wires.

Something I forgot to say but now I realize it could be important: I haven't yet received the male-female cable!

Actually I was so impatient that I tried with a normal female female cable, in which at one end I plugged this:


I've moved that black plastic to the middle of the pins, then plugged the pins in one end of the cable (so it looks like a male female cable) and to the TFT shield.

Now I realize the pins, with the black plastic, are a little short to go fully into both connectors, do you think it is the cause of my problem?

NickPyner


Did I just waste my money because an IDE cable can't handle the 5V required by the display (3.3V required by the backlight) ? I measured resistance between the 2 ends of some wires, multimeter show ~0.8 Ohms for each.


While IDE drives get their power by other means, I'm sure your ribbon should be capable of running a TFT, particularly over such a short distance. If your ribbon came with hardware each end, you have solved the biggest problem - the termination of so many tiny wires. But I don't understand the male/female bit. I thought all IDE ribbon was female each end.  I therefore don't think you are telling us the whole story, and what you are not telling us about could be where your problem lies.

Failing that, it could be a missing solder joint on a prototyping shield. I had one of those lately.

MarkT



Did I just waste my money because an IDE cable can't handle the 5V required by the display (3.3V required by the backlight) ? I measured resistance between the 2 ends of some wires, multimeter show ~0.8 Ohms for each.


If the cable really is 0.8 ohms its a dud.

More likely you are measureing losses and errors in your multimeter and its leads - to measure resistances less than about 5 ohms
I recommend passing a known current through the thing and measuring the voltage across it, R = V/I

Loose connections could cause enough voltage drop to dim the backlight, 15cm of wire shouldn't.
[ I won't respond to messages, use the forum please ]

liudr

Short pins could be a reason. Also long IDE cables are prone to interference. How long is your IDE cable?

NickPyner

#6
Nov 25, 2012, 01:07 am Last Edit: Nov 25, 2012, 01:09 am by NickPyner Reason: 1

Short pins could be a reason.


Indeed

I've just seen the picture. If they are being used as male/male adapters, I reckon they would be suss. You can probably push the pins through to make the lengths equal, and that might fix the problem.

guix

I've found the problem... I'm feel so stupid now!

Look that picture: http://i.solidfiles.net/7ed7dbbbe0.jpg

You see, it's working, but...

It's impossible to plug the IDE cable on the shield so the pins correspond on both sides! I mean, imagine if instead of those 2 wires, I had pins... I can't plug it because it will be inversed then! :(

I'm confused...will I have the same problem with an IDE male-female ??


I thought all IDE ribbon was female each end.
Think of it like an IDE cable extender!

Docedison

I found some 'Dupont' or standard color coded wire 40 pin 8" (20 cM w/ F/M connectors for $2.50 US on Electrodragon.
The Store has those W/Shells and the same type but  F/F W/O shells for about the same price and he sells a - 3 - 4... to 8 pin shells separately
These are really great for making your own cables. He also sells the male to male adapter pins (gender benders) too.
I use a 40 pin M/F to extend my 40 pin GLCD away from the shield so I can solder stacking headers to connect the Mega to the rest of the world.
It's a good idea to put the pins on and then wrap some cellophane tape around the 'body' of pins to keep good alignment if disconnected for any reason, As I found out the hard way.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

guix

I see, I think will do that too, as a bonus it will also allow me to fix the SD card bug (2 of the SPI pins are inverted on the TFT shield, so I just invert position of 2 wires and it will fix it...I think!).

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