What is on it
Two 5730-size white LEDs, warm and cool, each rated 150 mA and half a watt. Each has a 10 Ω resistor from VCC and an S8050 transistor on its ground side, driven through 1 kΩ from its pin. A 22 µF and a 100 nF sit across the supply. Nothing else: no regulator, no driver chip.
Eight parts and a header
Pick a part. The two flat rectangles at the top are the LEDs: 5.7 by 3.0 mm, the size called 5730, the kind used in LED strips and panel lights. Each is rated 150 mA continuous and half a watt, and spreads its light over 120°, so it lights a desk rather than a spot.
The two black parts at the top left are the 10 Ω resistors, one per LED, from VCC to its anode. They are the only thing that limits the current, and they are the larger 1206 size because at 5 V they run close to their quarter watt.
The two small three-legged parts in the middle are S8050 transistors, one on each LED's ground side, each with a 1 kΩ resistor from its pin to its base. The two brown parts are capacitors across the supply: 22 µF and 100 nF.
Why a transistor at all
An LED like this wants over a hundred milliamps. A microcontroller pin gives a few tens at most, and on a Pico 12 at its strongest setting. So the pin does not drive the LED: it turns a transistor on, and the transistor lets VCC drive it. The next article follows the current round that loop.
Why the capacitors
PWM switches each LED's current on and off hundreds of times a second. Every time it switches on, the current has to arrive at once. The 22 µF on the board gives the first moment of each pulse from a few millimetres away, which keeps some of that jolt off your jumper wires and your board's supply. The 100 nF handles the fastest part of the edge.
The warning on the back
The back prints EYE HAZARD, EXTREMELY BRIGHT, DO NOT LOOK DIRECTLY. The two LEDs together can put out about as much light as a small torch, from two small points. Look at what they light, not into them, and point them away from faces when you test.
When it does not work
That is the phosphor. A white LED is a blue LED under a yellow coating that turns part of the blue into the rest of the spectrum. The warm one converts more of the blue, which is why its light is warmer.
From the net list: the upper transistor, beside the upper 1 kΩ, switches the 6500K LED; the lower one switches the 3000K. They are the same part, so it only matters when you are probing the board.
No. The exported parts list names one green 5730 part for both positions, a placeholder. The board prints 3000K and 6500K and the photographs show two white LEDs; the ratings in this book are from the maker's warm-white and cool-white 5730 sheets, which agree on every number used.
Where the current comes from, and why it is not your pin.
The pin only switches it →Edit this page — content/books/dual-bright-leds/what-is-on-it.mdx
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