When working with electronics, breadboards are an essential part of experimentation, allowing you to swap out parts at a moment’s notice. Of course, standard boards need an external power supply of some sort, and if you don’t know the voltage input, you’ll need to check things out and/or hook up a multimeter. If that sounds a little too inconvenient, then Joe Wright's tiny Breadboard Voltmeter may be exactly what you need. This PCB-based device plugs into a power and ground supply rail, taking up only a single 2x5 block of breadboard connections. On top, 10 LEDs indicate the integer voltage from 3-12V, lighting up the appropriate LED next to a series of labels. Five 1kΩ resistors form a divider network to measure incoming voltage levels, which is calculated using a QFN-format ATtiny85V-15MT microcontroller. This format helps facilitate the board's overall small size, and the whole thing consumes under 3mA. Potential improvements for the voltmeter could include a programming header for the ATtiny85, as programming here meant a bit of detailed (and likely frustrating) soldering work. Wright also notes that non-integer voltages could be indicated by switching the brightness of adjacent LEDs, or that +12V, -3V could be shown by flashing the appropriate LED. Code is available on GitHub if you’d like to try your hand at something similar!