The three switches
Five voltages, three levers, and a table printed on the back of the board that agrees exactly with the chip's datasheet. The part nobody tells you is that the bar behind the levers says 0 and 1, not on and off.
The bar says 0 and 1
Look at the white bar behind the levers. It has a 0 printed at one end and a 1 at the other. That is the single most useful thing on the board, and it is easy to miss, because the switch body underneath also says ON in its own tiny lettering on the same side as the 0.
Both markings agree. Pushing a lever to that end closes the switch, which ties the chip's configuration pin to ground, which the chip reads as 0. Pushing it the other way opens the switch and the pin reads 1.
The board labels the level, not the switch, because the level is what the table wants.
The table
The same five rows are printed on the underside of every board:
| Voltage | Lever 1 | Lever 2 | Lever 3 |
|---|---|---|---|
| 5 V | 1 | X | X |
| 9 V | 0 | 0 | 0 |
| 12 V | 0 | 0 | 1 |
| 15 V | 0 | 1 | 1 |
| 20 V | 0 | 1 | 0 |
X means the chip stops reading that lever. Once lever 1 is at 1, the answer is 5 V whatever levers 2 and 3 are doing.
The order of the last two rows is the one people get wrong. 15 V is 0 1 1 and
20 V is 0 1 0, so going from 15 V to 20 V means moving lever 3, not lever
2. It is not a counting sequence and there is no point trying to remember it as
one — read the table, which is why it is printed where you cannot lose it.
The three levers are the three pins
Lever 1 drives the chip's CFG1 pin, lever 2 drives CFG2 and lever 3 drives CFG3. The numbers beside the switch on the silkscreen are the same numbers. There is nothing else to configure: no jumper, no solder blob, no firmware.
That table is the CH224K's own, from section 6.2 of WCH's datasheet, and this board's silkscreen reproduces it row for row. If you ever meet a different trigger board built on a different chip, do not assume its levers mean the same thing — the resistor-configured ones in particular use an entirely different scheme.
When it does not work
Either the levers are the other way round from what you think, or the charger has no 20 V rail. Check the levers against the table first: 20 V is 0 1 0, which means lever 1 pushed to the 0 end and levers 2 and 3 split. Then check the printing on the charger.
The end the white bar prints 0 at, which is the same end the switch body itself marks ON. Pushing a lever to that end closes it to ground and the chip reads 0. The opposite end is 1, and there the 10 kΩ pull-up decides.
No. All eight patterns of three levers name a voltage, because once lever 1 is at 1 the chip stops reading the other two and asks for 5 V whatever they say. The only mistake available is asking for the wrong voltage for your load.
They are meant to be moved with something small and hard — the corner of a flat screwdriver, a paperclip, a pen tip. Do not use a knife point; it slips off the lever and across the board. Push, do not lever, or you will snap the actuator off.
A 10 kΩ resistor up, a lever down, and the reason a switch on this board is read as a digit rather than as on or off.
Why a lever is a number →Edit this page — content/books/pd-trigger/the-three-switches.mdx
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