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Author Topic: IDE ribbon cable to link TFT display to it's adapter shield: bad idea?  (Read 1569 times)
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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.
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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/
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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?
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Dee Why NSW
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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.
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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.
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Short pins could be a reason. Also long IDE cables are prone to interference. How long is your IDE cable?
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Dee Why NSW
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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.
« Last Edit: November 24, 2012, 07:09:40 pm by NickPyner » Logged

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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! smiley-sad

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!
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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
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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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