Here is a link to a cheap digital voltmeter. Sorry I don't know how to make
it an active link.
https://www.allelectronics.com/index.php?page=seek&id%5Bm%5D=pattern&id%5Bq%5D=pm-126
it an active link.
https://www.allelectronics.com/index.php?page=seek&id%5Bm%5D=pattern&id%5Bq%5D=pm-126