Bus Pirate Ultra 2.8 inch display and the danger of Taobao suppliers

We’ve been prototyping the Bus Pirate Ultra with a 240 x 320 pixel 2 inch LCD, but it’s just a bit small and hard to read from a distance. A 2.8 inch version is available that fits the full width of the Bus Pirate PCB, with the trade off of bigger pixels/lower pixel density. We bought a few displays from various “manufacturers” on Taobao and made up a daughterboard. It failed spectacularly because the datasheet was so wrong!

Anode and cathode pin locations in the “datasheet”
Anode and cathode position on the actual display

We don’t have to go beyond pin 1 to find a major and obvious error. The datasheet lists pin 1 as the LED backlight anode, and pins 2-5 as the cathode. The printing on the flex connector makes it clear that four cathodes (K1-4) join into a single trace to pin 1. A single anode (A) trace connects to four pads on the connector (pins 2-5). The backlight connections are backwards.

Coincidentally, datasheets for other similar displays (2.8 inch, 50 pin connector) match the corrected pinout. This datasheet just had it backwards. We reversed the backlight power and ground on the PCB by drilling out a trace and creating some strategic solder bridges. While the LEDs light, the display doesn’t respond to any commands so other connections could be wrong.

That’s not all. The flex cable is actually several millimeters shorter than listed in the datasheet, so it can’t reach the connector through the slot in the daughterboard.

We had similar issues with this supplier’s 2 inch display. The dimensions in the datasheet are a bit off, and their sample initialization code doesn’t work. We asked for an updated datasheet and received three different versions, none of which matched the actual display.

Their Taobao page has pictures of a factory and a nice section on after sales support. A charitable guess is that they manufacture runs of custom displays, and sell the excess on Taobao. That would explain all the different datasheets they so readily have available. We tried to get another grab-bag of PDFs for the 2.8 inch display, one of which might match the actual pinout, but at this point they got tired and ghosted us.

Will we stop buying prototyping samples on Taobao and 1688? Definitely not! It’s a great way to see what’s a cheap commodity product. This process plays out in the Shenzhen markets as well, people sell a lot of stuff without knowing exactly what it is. It’s kind of up to us to know what we’re buying, and sometimes it’s a crapshoot. When we find a sample we like, it’s time to send someone up to the factory to meet the boss, drink way too much tea, and ensure we’ll have a steady and consistent supply in the future.