ElecFreaks TFT01 mega shield question

Other Hardware Displays
1

I stumbled upon something that has me puzzled... I was testing a new 5 inch tft display plugged into a Elecfreaks TFT01 shield on a Mega 2560. I had loaded the latest UTFT and was using the all functions test demo, everything looked good.

Ultimately, I wanted to use the pwm backlight control and I wanted to see what the default, non-controlled brightness level looked like. I loaded an empty sketch, unplugged the USB cable and plugged it back in and I had a nice, blank backlit display. After approximately a minute or so, I looked over and saw the blank display going nuts - changing intensity, random pixels appearing, the entire screen then faded to black and things looked... well, like something failing. Aggghhh!

I very quickly unplugged the USB cable. I started with the sniff test then popped the boards apart and touched all the chips. Nothing hot, nothing smoking. Everything looked okay so I thought the next step would to check voltages at the shield without the display. The 3.3 volt regulator was okay, all the signal pins were zero or 3.3 volts. But, when I got to pin 2 of the 40 pin tft connector, the main vcc supply to the display, it measured 5 volts! I checked the back of the tft display board and the white legend printing clearly showed "3.3v". The shield schematic does not show the 3.3 volt regulator so I traced out the board (made more difficult with the white solder mask) to find that the vcc pin was in fact tied to the +5 volt pin of the Arduino.

I ended up cutting the trace and moving the display power over to 3.3 volts and the display is working fine. But, this leaves me wondering. Are most of the tft displays out there 5 volt supply with 3.3 volt logic levels? There really isn't any doubt about this display since the board is clearly marked 3.3 v. I checked the other tft modules that I have on hand and one is marked "3.3 v" the others are marked "vcc". I checked the modules marked vcc and they appear to work fine with a 3.3 volt supply.

Has anyone else encountered this with other shields? Do others have a supply voltage jumper?

2

Yes I did have the problem of the screen freaking out after a minute or so then after more playing with it it started happening much sooner. I have the 7" TFT touch SD combo from elecfreaks. I however found that the 5v regulator on the arduino wasn't enough to run that 7" screen (back light) and try to do anything else at the same time. Really i haven't studied the shield much as i observed this by monitoring the arduino voltage and a drop correlated with a freak out so to speak. I cut the pins for the 5v and for the 3.3 then soldered leads on to the shield that hooked to a computer power supply for lab testing then used wall power supplies for final project and haven't had any problems.

NOTE I never could get the SD card to work right with the shield wiring so i had to mod for that too.

3

can you please show how you connected your shield to the external power supply (i.e. what pins did you connect to the external power supply and some schematic or a picture to the connection if you please), and can you please tell me the current that was flowing through both 5V and 3.3V connections coming from the power supply.