kershner
Posts: 23
Joined: Sat Jun 07, 2014 8:54 pm

Anyone have experience with this 3.5'' LCD?

Sat Jun 21, 2014 8:52 pm

http://www.amazon.com/gp/product/B0045I ... UTF8&psc=1

I'm trying to hook this one up to my Pi but am not having any luck. I think I've narrowed it down to either my power supply is wrong or the screen arrived DOA. Can anyone with experience offer some advice on the screen?

The power supply I bought is this one:
http://www.amazon.com/gp/product/B000Z3 ... UTF8&psc=1

It's only .5 amps and I saw some unsubstantiated rumor on the Amazon page that this screen requires 1A, would that make the difference? There is also a warning about getting the right 'polarity' when putting on a new barrel jack tip. As there were no instructions with the LCD, I tried both polarities - could that have fried the screen?

Edit: Just thought of something - is it possible that the Pi is simply not detecting that there is a video input? Maybe something I have to edit in the boot config file? These LCDs won't power on at all unless they have a video signal.

Thanks for any help!

User avatar
joan
Posts: 14378
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Anyone have experience with this 3.5'' LCD?

Sat Jun 21, 2014 9:12 pm

What voltage are you feeding to the display?

User avatar
FLYFISH TECHNOLOGIES
Posts: 1750
Joined: Thu Oct 03, 2013 7:48 am
Location: Ljubljana, Slovenia
Contact: Website

Re: Anyone have experience with this 3.5'' LCD?

Sat Jun 21, 2014 9:18 pm

Hi,
kershner wrote:It's only .5 amps and I saw some unsubstantiated rumor on the Amazon page that this screen requires 1A
Take a voltmeter and measure the power supply voltage at free run (it should be set to output 9V or 12V). Then measure the voltage when supplying the LCD. If this voltage is lower more than (lets say in case of this LCD) 1V, then your power supply is overloaded and you need one more powerful.
kershner wrote:I tried both polarities - could that have fried the screen?
Electronics is not a member of bingo games club. ;-)
Yes, it could be that you fried the screen...


Best wishes, Ivan Zilic.
Running out of GPIO pins and/or need to read analog values?
Solution: http://www.flyfish-tech.com/FF32

kershner
Posts: 23
Joined: Sat Jun 07, 2014 8:54 pm

Re: Anyone have experience with this 3.5'' LCD?

Sat Jun 21, 2014 10:45 pm

joan wrote:What voltage are you feeding to the display?
The power supply is set to 12V. I'm not sure what 'polarity' to use on the barrel jack tip, though.

User avatar
MattHawkinsUK
Posts: 538
Joined: Tue Jan 10, 2012 8:48 pm
Location: UK
Contact: Website

Re: Anyone have experience with this 3.5'' LCD?

Sun Jun 22, 2014 7:00 am

I've got a couple of those screens. They are 12V centre-positive. Make sure they are connected before you boot the pi and there is no HDMI cable connected.
My Raspberry Pi blog and home of the BerryClip Add-on board : http://www.raspberrypi-spy.co.uk/
Follow me on Google+, Facebook, Pinterest and Twitter (@RPiSpy)

kershner
Posts: 23
Joined: Sat Jun 07, 2014 8:54 pm

Re: Anyone have experience with this 3.5'' LCD?

Sun Jun 22, 2014 1:53 pm

Centre positive, I'm guessing this was my mistake, since I didn't know what polarity to apply before connecting (so I tried both). I'm guessing that fried the screen?

I'll have to grab a new one and try again. For future reference, how can I tell what polarity a device needs?

Thanks for the input, by the way.

klricks
Posts: 6609
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: Anyone have experience with this 3.5'' LCD?

Sun Jun 22, 2014 2:13 pm

Hopefully the device has a reverse polarity protection diode.

If you are running NOOBS then a config file needs to be edited or else HDMI will be forced.
http://www.raspberrypi.org/forums/viewtopic.php?t=56815

Be sure to use the yellow input. The other input is meant for a reverse camera and will not show anything unless the reverse circuit sense wire is also connected to 12V.

Your Amazon listing states power supply of less than 4W which would be 0.333A at 12V.
Last edited by klricks on Sun Jun 22, 2014 4:17 pm, edited 1 time in total.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

kershner
Posts: 23
Joined: Sat Jun 07, 2014 8:54 pm

Re: Anyone have experience with this 3.5'' LCD?

Sun Jun 22, 2014 4:11 pm

Posting here to mark this topic as SOLVED.

Klricks pointed me in the right direction - the /boot/config.txt file needed to be edited, under the NOOBs auto-generated settings.

#hdmi_force_hotplug = 1 # Commented out line to allow composite detection

Now the display works just fine, and my project is back on track. Really appreciate all the help here, you guys rock.

Return to “General discussion”