Smallest possible text display


I have a crasy idea - I want to have my model railroad trains get real destination displays. I am using TT gauge, so 1:120 scale. I would need some display 15-22 mm long and 3-4mm high, without serious framing and requiring as little wiring as possible (I2C or similar). Maybe text only. As a controller I thought on digispark or pico...

The train decoder has exits which can toggle depending on direction, or exits which could be used to select the destination. Even a primitive serial like protocol like (exit one on - listen up!, exit one toggling up and down at 0.1 s intervals to get the code through) possible.

The displays would be in both cabs where the destination is shown on real train, and also if possible on the sides, where the regular trains also have the destination displays.

Any suggestions on such displays?

Tha smallest i have seen is this one:

The smallest display might be this:

It is available also on the usual market places. I suggest you order this display together with the PCB breakout board. The OLED seems to be fixed on the PCB with some glue, so I assume the OLED can be detached from the PCB.


4mm high? That's definitely custom display technology, you'd have to pay a lot. Unless someone else has
made one already for similar reasons. Would also make a great head-up display for a squirrel!

4mm high? That's definitely custom display technology, you'd have to pay a lot.

$4-$5 on ebay for the 0.42" Oled


That 0,42 inch oled looks not bad! I will make a paper template for it and see if it fits. For the variant with the board, can the board be placed separately (I mean, OLED in the train target area, board under the roof)

There would be not much space however.... here's the train - display is narrow over the cabin... ODEG-650 083

I fear the 0,42 would be too high for the front, it would however work for side displays. Something in this size but longer and narrower would be better for top...

Just had an idea - do you guys think placing a triangular prism in front of display would help? I mean, display is flat on the ROOF of the wagon, wedge prism is on it, with wider side on display and narrower side in the place where the train display is...

That should work.

There is some glue between the OLED and the PCB. I just made some pics with the OLED in my lab.

This is the original oled with a 10 Eurocent coin and a cm scale. There is still the green foil display cover on the OLED.

There is some double glue tape between OLED and PCB

So the OLED can be placed on some roof top (display cover foil removed) :o


You can buy the bare module but it will still need a few external capacitors and resistors. Look at the Blue pcb in Oliver’s photo.

It will be difficult to fit a small display inside a TT model.
Use a prism or a mirror to get the visible result where you want.

Life would be easier with OO gauge.


I obtained the Digispark, 0,42 display, and a pair of 5x5x5 reflecting prisms today. When these will arrive, I will see what I can do.