Hi,
I've finished coding a project that uses a 5 inch display with Henning Karlsen UTFT library.
It works really well but now that I've taken it off the usb cable and plugged in the 12 VDC/1 Amp power supply, the graphics image loading from the sdcard is corrupt. The rest of the graphics are good. Reset button results in exactly the same. When I put it back on USB it's okay.
Anyone have any similar experiences ?
Please describe your hardware. i.e. Arduino type and Display model (and Adapter Shield model) . preferably with links to the manufacturer or Ebay listing.
I am guessing that you have a MEGA2560 powered by the USB cable. I would hope that your 3.3V display has appropriate level converters etc for the Arduino's 5V GPIO.
If the USB cable is disconnected and you power the MEGA2560 by the 12V barrel-connector socket, the Arduino's onboard voltage regulator chip will provide the same 5V as the USB provided.
So it should not make any difference to the microSD card.
Many "Display" boards simply provide 3.3V for the microSD's VCC terminal and let the individual card cope with 5V logic signals. Some cards are more tolerant of 5V logic than others.
Other boards will have specific level-converter chips to ensure that the card only sees 3.3V logic.
Some other boards may just provide series resistors.
David.
Hi David,
Arduino Mega (Funduino) as guessed, Sainsmart 5" tft, no shield - everything wired directly to the screen from the mega 36pin i/o header. All running fine on 5v. I know it should be 3.3 but doesn't work well. Barrel connector - I've tried 9V 3A and 12v 1A (overheats) and I get the same corruption. I've also tried powering the screen and screen led on a mix of 3.3 and 5v without luck except that the screen led wont work on 3v. In what way could there be a difference between the barrel jack and the usb ?
I have no idea how your Sainsmart 5" TFT schematic is like.
Since Sainsmart want you to use an adapter shield e.g.
http://www.sainsmart.com/sainsmart-extend-tft-lcd-shield-for-arduino-mega2560-5-7-inch-lcd-display.html
I would think that the bare display is NOT 5V tolerant.
It is up to you. If you want to destroy your display and/or microSD cards, run them at the wrong voltage.
As I said, I have no idea how your module or chips are configured. Sainsmart do not seem to publish schematics.
5V derived from USB is the same as 5V derived from a voltage regulator. However, when you apply 5V GPIO outputs to 3.3V inputs, you force the substrate diodes to conduct. This tends to take the substrate up towards 5V rather than lose the voltage across the diode (if there is no series resistor).
Pure speculation on my part. I do not own your display. I would certainly be wary of any manufacturer that has a policy: "We will supply you the technical support after your purchase."
David.
Thanks for your input. I've been running one of these displays on my aquarium for over 9 months now all on 5v - all good. That one works harder than the current project as it's on continuously (247) and is constantly loading large .raw files from the sdcard. If I was going to have over-voltage problems, then I would have seen them by now.
Despite the bad reputation Sainsmart has, their products are cheap and they do supply all the documentation even though most of isnt their property (Henning Karlsen) and communication (language) is a barrier. Sainsmart shields arent so good as I couldnt get my display to work with them at all. They eventually replaced my existing display so now I have two, and they both work apart from this glitch which I have now resolved.
All the best.
How have you "resolved" the problem?
Using level translators will comply with the spec for the microSD and for the TFT controller.
Relying on series resistors to limit the current through substrate diodes is not ever "approved" by any chip manufacturers. OTOH, it works in practice. i.e. it ensures that the voltage limits are not exceeded.
Only you know what electronics / schematic is contained in your display. And what is present in the purpose built Adapter shield.
David.
nosomis:
Despite the bad reputation Sainsmart has, their products are cheap and they do supply all the documentation even though most of isnt their property (Henning Karlsen) and communication (language) is a barrier. Sainsmart shields arent so good as I couldnt get my display to work with them at all.
Correction........... they USED to be cheap, now they charge mainstream prices while providing subferior products, that intellectually don't belong to them as you correctly mentioned. The shields last time I checked are clones of CTE shields which are certainly the best on the market, and yet CTE charge less for a GENUINE CTE shield than Saincrap charge for a copy!!! You pays your money I guess..... And get what you deserve...
Don't forget, they got their reputation through their business practices and repeated requests on these forums from poor unsuspecting newbies that didn't realise when they saved themselves $5 by buying from Saincrap that they were heading for a boatload of problems!
My first Arduino package came from Sainshit, I will never use them again. Aliexpress sell the same stuff and cheaper, just saying....
Regards,
Graham