Easy variable voltage power supply

-A 30-32v power adapter. (Mine is salvaged from an old printer)
-A DC-DC buck converter. (1$ on ebay)
-A LED panel voltmeter. (2$ on ebay)
-An audio spring terminal. (0.40$)
-A potentometer, the same value as the one of the converter, mine is 10K (0.60$)

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