Is this 3.3V or 5V? (dealing with Arduino, STM32 and others)

[KansaiRobot]

Hello.
I would appreciate some help in a problem with voltages.

First, I am using this TFT LCD
**broken link removed**
I know, I know, it is in japanese sorry. I ll translate for you:

LCD Shield (3.5）[ML035TF-TP]

->Specs& Functions:
Finished product targeted to the Arduino Mega2560. Pin header fully assembled, making it ready to use.
Display Resolution 240x400
LCD controller chip ILI9327
8 bit parallel data bus.
micdo SD socket mounted.
Touch controller chip XPT2046
Touch screen function available

Operation Power 3.3V

Ok, first question: Arduino Mega (and Arduino UNO) works with 5V based pins, right?? but this shield "that is ready to use" operates at 3.3V???

Second, I have successfully used this with the UNO. pins were connected directly. I am confused at this because I powered the shield with the 3.3V pin however the IO pins were connected directly. So were this 5V based???
(I checked with an oscillator and yes in fact, it is 5V based... but the power by the 3.3V pin was correct???)


Third I am trying to interface this and make it work with a STM32 nucleo that is entirely 3.3V and it does not work!. So maybe 5V are required??? 3.3V would not give a HIGH for pins that wait for 5V right?

Note that this product does not have a schematic but now just with my eye could see a AMS1117 chip there.... What is this chip doing there??

Any comment or even question will be greatly appreciated

 

[DirtyLude]

I'm assuming ILI9327 is similar to the ILI9341 which are all over ebay. The arduino shield ones all have a 3.3V regulator on board and are using the 5v power regulated down for main power. There is some discussion with using 5V data lines on these and it is out of spec, but it looks like it works fine as there are a lot of these and I don't believe they are level shifting the data lines.

If this is using a regulator on the power line and you are powering it with 3.3V, the voltage drop over the regulator might be underpowering it.

The ebay ILI9341 ones are one of my favorite displays, but I avoid the arduino shield versions.

 

[BobW]

I've recently seen some other Arduino "shields" that turn out to be 3.3 volts. So I wouldn't be surprised.

 

[ericgibbs]

hi.
The Arduino shields I have, use a 74HC125 as a 5V to 3.3V 'down level' shifter for driving 3.3v signal devices.
As Bob points out, they also have 3.3V onboard regulator for powering the 74HC125 and peripherals.
E

 

[KansaiRobot]

hi.
The Arduino shields I have, use a 74HC125 as a 5V to 3.3V 'down level' shifter for driving 3.3v signal devices.
As Bob points out, they also have 3.3V onboard regulator for powering the 74HC125 and peripherals.
E

Unfortunately this thing does not come with a schematic. But I can see with my raw eye that there is a AMS1117
http://www.advanced-monolithic.com/pdf/ds1117.pdf in the TFT. I wonder what for (maybe for the SD card??)
Anyway... I am confused.

I tried my program with my other TFT which is entirely and clearly marked 3.3V and it works without problems...

Perhaps I should avoid the "for arduino" TFTs...

 

[ericgibbs]

hi KR,
I guess you know that the AMS1117 is a 3.3v regulator.?
On my Arduino SD Card/DS1307 shield PCB there is a LPF3, a 3V regulator for the SD card power and a 74HC125, powered by 3v, for level shifting the SD input signals from 5V down to 3v.
I also use some 'stand alone' small SD card PCB's which use a AMS1117 to power the SD card PCB.
For down level shifting I have used resistive dividers 2K and 3k3 to reduce the 5V signals from the 18F4520 to 3.3V.
For the MISO output of the SD I have a 10K pull up to 5V.

For reference I have found that the Neo GPS card has on board a AMS1117 and a resistive divider is required for down level shifting of the RXD input signal.

If you examine the copper track on the PCB's its possible to check the path of the signal lines and using a PDF of any onboard i/cs you can determine whether a level shift is required.

Eric