Problems interfacing Teensey 3.1 to HY-1.8 SPI TFT display

[jomac]

My friend and I both have a couple of teensey 3.1, and an assortment of the popular HY-1.8 SPI TFT displays. There are mainly 2 types of 1.8" display, the 16 pin and the 10 pin. For quite a while now, weve been trying to get these to work and neither of us has managed to get anything to show on the screens. Im very much a novice, but my friend is a seasoned hardware guy and he's given up after spending 2 days on this.

The first attempts were using the Adafruit files from here... https://www.adafruit.com/products/358 This is intended for the 10 pin display but doesnt seem to work.

Then trying to get a generic 16 pin again using adafruit libry files from here... https://github.com/adafruit/Adafruit-ST7735-Library

and here... https://github.com/adafruit/Adafrui...master/examples/graphicstest/graphicstest.ino

The script compiles and verifies ok, and we can upload without a problem, once the software is running, the orange LED will flash a few times for about 30 seconds then nothing. There isnt the slightest hint of anything on the screens.

I could understand if it was just me having problems, but my friend who has streets more experience then me also having problems, i dont understand. Does anyone have any clues or a link to a foolproof set up that definately works?

Any help would be immensely appreciated.

John

 

[MichaelMeissner]

Just checking the obvious, have you checked whether your display needs 5v instead of 3.3v?

<edit>
And also, can the Teensy power the backlight from a data pin?

 

[jomac]

Well i dont really know what to say here Michael, The datasheet said simply VCC for pin 2 (16 pin version) but clearly said 3.3v for the LED supply, the Teensey being 3.3 volts, everything was set for 3.3v. A further note on the datasheet said to join the link for 5v nothing more.

Your comment above got me thinking, surely it cant be 5v VCC supply and everything else is 3.3v, or can it???

I took a gamble and shorted the link on the back of the LCD marked LP1, and connected pin 2 to 5v VCC and it works.

I just wonder how many others have fallen foul of this, at least to me it wasnt obvious.

Thank you very much for the help Michael, its very much appreciated, even though im a bit red faced

 

[MichaelMeissner]

You are welcome. When I went looking for LCDs, the great majority were 5v (and since many of them are marketed for the Arduino market it makes sense). A few LCDs would explicitly take 3.3v power.

I have a non-graphic i2c 16x2 display that can be signaled via 3.3v i2c, but it needs 5v power for the LCD, particularly to power the backlight, which is why I thought of it.

Most of the OLED devices do take either 3.3v or 5v, so it is a lot easier to set up one of those devices, and to shared the device between Teensys and 5v processors.

Obviously if you plan to power the Arduino via a 3.7v li-poly battery, the LCD might not work, without boosting the voltage to 5v. If you read from the LCD (most LCDs are write only), you need to take precautions if you are using a Teensy 3.0. Fortunately, the Teensy 3.1 has 5v tolerant digital pins.

 

[jomac]

Problem solved

The Teensey should power the LED back light as that is 3.3 volts, the same as the outputs and current is low. I went back over the information i had at hand to see why and where we went wrong, and if you make certain assumptions (as we did) its possible to end up with this problem.

It was only by harvesting little bits of 'part' information, and your comments that helped the penny drop. I did a quick sketch of the connections and how its set up now if that's of any use in helping others?