ST7735 Display - SPI or I2C?

Hey there,

i ordered a couple of ST7735 displays on ebay. I thought that the ST7735 controller connect by SPI and the displays were advertised as SPI displays, but the displays I got, have I2C connectors by their markings.
I attached an Image of the front and back of the display pcb.

Can someone tell me how to hook them up?

Your display uses SPI with a single bidirectional data pin called SDA.

Most libraries treat the SDA pin as write-only. They make no attempt to use it for reading.
AVR hardware and Atmel ARM hardware is not capable of "bidirectional pin"

From your photo, U4 looks like 3.3V regulator chip but it might be a transistor for switching the backlight.
What are the values of R1, R5, R6 ?

I suspect that you can connect VCC pin to 5V (if U4 is a LDO regulator)
If U4 is a transistor, it is safer to connect VCC to 3.3V
I suspect that the signals must have 3.3V logic e.g. with Zero, Due, STM32, ...

I have never seen this board in real life.
Only an owner can identify U4, R1, R5, R6.


Thank you very much for your reply!

Markings on the components are:

R1: 100
R5: 102
R6: 103
U4: J3Y (so I guess its a transistor)

I was planing to use an esp8266 anyways, so supplying it with 3.3V Vcc and logic is not a problem.

R1: 100 10R
R5: 102 1K0
R6: 103 10K
U4: J3Y (NPN transistor)

Yes. Connect VCC to 3.3V. SCL=SCK. SDA=MOSI. RES=gpio. DC=gpio. CS=gpio. BL is probably ok with n.c.

U8g2lib or Adafruit_ST7735 libraries should work fine.
Oops. Of course Bodmer’s TFT_eSPI library is your best choice for ESP8266.


Edit. Ebay has this display with connection details
Looks like my guesswork was correct. i.e. 3.3V only

Thank you very much again, it works perfectly!