Set it with a meter
Supply on VIN, nothing on OUT but a meter. Turn the trimmer down to its stop, then slowly up until the meter says the number. It turns three quarters of a turn, not ten, and with too little input most of that travel does nothing.
Before anything is connected
- Supply on VIN and GND, at least a volt above the voltage you want.
- Meter on DC volts: black probe on GND, red on OUT. Nothing else on OUT.
- Turn the trimmer with the screwdriver from the box, a little at a time, in whichever direction makes the reading fall, until it stops falling.
- Now turn the other way, slowly, until the meter reads your voltage.
- Connect the circuit, and read the meter once more.
Why so much of the trimmer seems dead
With 5 V in, OUT cannot go above about 4 V. The trimmer's setting keeps rising as you turn it, but the output stays pinned a volt below the input — so from there to the stop, turning changes nothing on the meter. Add the dead tenth at each end of the travel, and a reader with 5 V on VIN can turn the trimmer through most of its range and see nothing happen at all.
That is not a fault, and it is not a ten-turn trimmer taking up slack. It is the headroom from the volt it needs, showing up in a new place.
Which way is up
It depends on the board, so do not rely on a rule. Turn a few degrees and watch the meter. The screwdriver stays square in the slot; the trimmer is 3 mm across, and a slipping blade moves it further than you meant.
Write it down
The board has no LED and nothing printed about its voltage, so the white panel on the back is the only record. Write the voltage there the moment it is set.
Under load the reading barely moves: the datasheet allows a change of up to 18 mV from 10 mA to a full amp. If it drops by more than that, the input is sagging — measure VIN with the load running.
When it does not work
Check three things. The meter's black probe is on GND and the red on OUT. The input is at least a volt above the voltage you want. And the trimmer is not sitting in the dead tenth at one end of its travel — turn it a quarter turn the other way and try again.
Small jumps are normal on a trimmer this size: the wiper is a contact sliding on a track. Turn slowly, stop just past the number, and come back to it. Once set, it stays put unless something knocks it.
That advice is for a multi-turn trimmer, and this is not one. It stops after about three quarters of a turn. Forcing it past a stop with the screwdriver can break it, and the board is then stuck at whatever voltage it broke at.
The 3V3 board on a breadboard, fed from the Uno's 5 V, and a sketch that measures it.
A 3.3 V rail from an Arduino Uno →Edit this page — content/books/ams1117/set-it-with-a-meter.mdx
Questions about this product
See what other owners have asked, and read their solutions.
AMS1117 LDO Regulator Kit, 24 Boards (18 × 3.3 V, 6 × Adjustable)
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