What your supply must give
Both LEDs at the book's cap take about 224 mA from 5V, averaged; held fully on, about 336 mA. A computer's USB port promises 500 mA, and your board takes its share first. From a 3.3 V pin the two take about 123 mA from the regulator that also runs your chip, which an Uno's 3.3V pin cannot give and an ESP32 shares with its radio.
The block's share of your supply
Everything the LEDs take comes from the pin VCC is on. Pick your board, the pin, and how the LEDs are driven.
On 5V (VBUS on a Pico) the current comes from USB. At 170 of 255 both LEDs together average about 224 mA; held fully on, about 336 mA. A computer's USB 2.0 port promises 500 mA, and your board takes its own share of that first, so capped is comfortable and full on is not. A phone charger or a powered hub usually gives more.
It arrives in pulses: each is the full 168 mA per LED, hundreds of times a second. That is what the 22 µF on the block is for, giving the first moment of each pulse from close by.
The 3.3 V pins
On 3V3 each LED takes about 62 mA fully on, both about 123 mA, and it comes from your board's own 3.3 V regulator, the one that runs the chip.
- Uno: its 3.3V pin is good for 50 mA. One LED takes more. Never.
- Pico: 3V3(OUT) should stay under 300 mA, shared with the RP2040 itself, by its data sheet. Both LEDs fit.
- ESP32 and ESP32-S3 boards: the regulator also feeds a radio that takes a few hundred milliamps in bursts while Wi-Fi is on. It usually copes; if the board resets when the LEDs light, move VCC to 5V.
Which to choose
5V for the most light, with the sketches' cap. 3V3 for a light that can stay fully on and runs cool, at a little under half the brightness, on any board but an Uno.
When it does not work
Its 3.3 V regulator is feeding the LEDs and the chip at once, and Wi-Fi adds bursts of a few hundred milliamps. Move VCC to 5V, which comes from USB rather than through the regulator, and keep the duty at 170 or under.
From a 5 V power bank on the board's USB, yes. From a single lithium cell on a 3.3 V board, VCC on 3V3 gives about 62 mA per LED fully on; at that rate a 1000 mAh cell lasts a few hours with both lit, less the board's own draw.
For this block alone, on short jumper wires, the 22 µF and 100 nF on the board are enough. With long wires or several power-hungry blocks on one supply, a 100 µF or larger across 5V and GND near the blocks helps.
The short list of reasons it does not light, dims wrongly or resets your board.
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