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Main => Main Forum => Topic started by: grippie on November 16, 2015, 07:25:48 pm

Title: Convert 12v screen to use 5v - need help with voltages
Post by: grippie on November 16, 2015, 07:25:48 pm

I have a 4.3 inch screen I purchased for my portable raspberry pi project.
http://www.amazon.com/ePathChina%C2%AE-TFT-LCD-Rearview-Pocket-sized-Automobile/dp/B006JY4TQW/ref=sr_1_1?s=car&ie=UTF8&qid=1447719220&sr=1-1&keywords=ePathChina%C2%AE+4.3+Inch+TFT-LCD+Car+Rearview (http://www.amazon.com/ePathChina%C2%AE-TFT-LCD-Rearview-Pocket-sized-Automobile/dp/B006JY4TQW/ref=sr_1_1?s=car&ie=UTF8&qid=1447719220&sr=1-1&keywords=ePathChina%C2%AE+4.3+Inch+TFT-LCD+Car+Rearview)]

I found the diagram for the IC that has pin 2 as the 5v power. (image 1) I read a lot of tutorials that simply state to disconnect the red power input from the 12v line and solder it directly to the leg on the IC for 5v input.

The screen needs 4.7v minimum to power on and everything looks good from a connection standpoint (the picture looks like the solder is bridged between pin 1 and 2, but that was just some loose solder that i blew off before connecting) I cut the 12 volt wire, (red wire from the cable) and soldered a new wire to the 5v in (pin 2) on the IC. Then I added another ground wire to the existing ground connection just so i didn't have to tear the video cable down all the way just yet. This way i can make sure everything works and isn't just my cable modifications.

So in summary I have Power from a micros USB cell phone cable --> powerboost 500C --> USB output at 5.12 V --> wires going from the USB output to the 5v in on the IC on the monitor and ground from the USB output to the shared ground on the monitor pcb. Those connections measure 3.3v if i connect the ground and the solder point that is attached to pin 2. I'm not sure why it's showing 3.3v at this point and i'm suck. Any Ideas???

Title: Re: Convert 12v screen to use 5v - need help with voltages
Post by: matsadona on November 20, 2015, 08:58:05 am

Probably it isn't that simple that you can put 5V on the output pin... as you see in this typical diagram there are some more components:

(http://www.sanfo88.com/upfiles/201506/03/a9b73fa39423d41f6.jpg)

So if you need to do this kind of hack I would have searched for the V+ pin on any other IC on the board that you know is using +5V and tap it in right there.

Also note that there might be more than one regulator and voltage on the same board. 3.3V is a typical low level voltage for some logic circuits and CPU's, so perhaps that is something that needs to be there as well.