3.3 V or 5 V
VCC decides two things at once: how bright the panel can get, and what voltage the two signal wires idle at. That is why a blue panel disappoints on 3.3 V, and why feeding the display 5 V beside an ESP32 is the one arrangement to avoid.
One pin decides both
The board's two 10 kΩ resistors pull CLOCK and DATA up to VCC. The display's LEDs sit between VCC and the chip's outputs, with no resistors in the way.
So the single wire you put on VCC sets the voltage on your board's two input pins and the voltage available to light a segment. Those two want opposite things on a 3.3 V board, and that tension is this whole article.
What the colours need
An LED does not light gradually as the voltage rises; it needs its forward voltage before it conducts at all, and that voltage depends on the colour.
| Colour | Wants about | On 3.3 V | On 5 V |
|---|---|---|---|
| Red, orange, yellow | 2.0–2.1 V | Fine | Fine |
| Green | 2.2 V, or nearer 3 V for a true green | Usually fine | Fine |
| Blue, white | 3.1 V | Barely on | Fine |
Those are the typical figures for the colour rather than a measurement of these panels, and there is a second drop on top of them: the chip's own output transistors take a share. Titan Micro's datasheet is blunt about where that leads — it specifies the chip at 4.5 to 5.5 V, and notes that a blue display needs a 5 V supply.
In practice the chip's logic runs happily on 3.3 V, and a red panel on a Pico or an ESP32 looks perfectly good. It is the colours at the top of that table that run out of voltage, not the chip.
The three ways to wire it
An Uno, or anything 5 V. VCC to 5V and there is nothing to think about. All six colours, full brightness, signal wires at 5 V where the board expects them.
An ESP32, a Pico, an ESP32-S3 — VCC to 3V3. Correct and safe: the signal wires idle at 3.3 V, which is what the pins want, and the chip is fine. Use a red, orange, yellow or green panel and it looks good.
An ESP32 with a blue or white panel. This is the only case that needs anything extra. Feed the display 5 V for brightness, and put a bidirectional level converter in CLOCK and DATA so your board's pins only ever see 3.3 V.
The converter has to be the kind that suits lines held up by resistors — a MOSFET-based one, or a TXS-type buffer. A TXB-type buffer fights a pull-up and is the wrong part here; which board for which job is the argument in full, and a 5 V screen on an ESP32 is the same wiring with a different part on the end of it.
What not to do
Do not feed the display 5 V and wire CLOCK and DATA straight to a 3.3 V board. It will work. It will keep working for a while. The pull-ups are 10 kΩ, so the current going into the protection diodes on your board's pins is small — which is exactly why the failure is slow, undramatic and impossible to diagnose three weeks later.
When it does not work
Both are working. A blue or white LED needs about 3.1 V before it conducts at all, and there are no series resistors on this board, so on a 3.3 V supply there is almost nothing left for the chip's own transistors. Red, orange and yellow want about 2 V and are fine. Move the blue one to a 5 V board.
It appears to. The board's pull-ups hold CLOCK and DATA at VCC, so from 5 V those two pins sit at 5 V against inputs rated for 3.3 V. That damage is cumulative — boards that ran like this for weeks and then became flaky are a common story, and by then nobody connects the two.
Not directly: the board pulls both wires up to its own VCC regardless of what your board does, so they will still idle at 5 V. A bidirectional level converter in the two signal lines is the way to do it, with the display's VCC on 5 V and the converter's low side on 3.3 V.
Greens vary by chemistry more than any other colour — a yellow-green runs at about 2.2 V and a true green nearer 3 V. If your green behaves like the blue one rather than like the yellow one, it is the second kind, and it wants 5 V.
Six displays, one clock pin, and the spare holes that quietly make them all show the same thing.
More than one display →Edit this page — content/books/tm1637-display/three-volts-or-five.mdx
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