DIY Decade Resistance Box

According to creator sunyecz06, starting a project typically “involves sifting through multiple components, including the endless, tangled mess of resistors I have in my drawer.” As you can imagine, this is a time-consuming and frustrating process, especially if you don’t quite have the standard resistor color codes memorized.

For easier prototyping, sunyecz06 made his own decade resistance box, using a new custom PCB design, SMD resistors, and a series of mechanical decade counters that had been sitting unused in his component bin. One PCB and counter is implemented for each resistance stage, all of which are soldered together to make a unit that can be set between 1 and 9,999,999 ohms.

Each counter selects the appropriate resistance to apply in series to the overall box output, which is connected to the next counter/resistor in series, and so on over seven resistor stages. This overall resistance can then be applied to an external circuit for testing.

Once a proper value is established, then suny’ can sift through his drawer (one time) for the proper resistor. He does note the device exhibits some error due to either the limits of his multimeter or resistance tolerance, though this only amounts to around ±5 ohms at the lower end of its range.

Of course, if you search around for “decade boxes” or similar, you can just buy one. At the same time, they’ll set you back around $100, and won’t give you the satisfaction of making it yourself, or the neat resistor color coding that suny’ painted onto his device. You’ll also still have those decade counters occupying space in your parts bin!