PCB Friday: Jumper Options to Modify Your Circuit's Operation

When you design a PCB, you may have one use in mind. Or you may have a series of dials and switches that an operator can change as needed to adjust its operation. But there are also times when one circuit board needs to be set up for testing or semi-permanent configuration via connectors known as jumpers.

Jumpers can be formed from simple lengths of wire, or dedicated "cap" connectors that are applied across adjacent header pins. You can also use a zero-ohm resistor, or solder two nearby pads together for a "no-BOM" solution. It's a simple concept, but there's a lot to consider when applying them. Read on to find out more!

Jumper options

So as not to bury the lede — or lead wire — jumper options are listed below. Commentary follows... which you can choose to ignore if you are so inclined:

• Jumper wire: The most versatile option on this list. If you have a series of header pins on your board, you can simply connect them together with jumper wires regardless of the board positions. For instance, if you want pin 8 on your Arduino UNO to read as low, just pop in a jumper wire from there to ground.

• Pin header cap/shunt: If you have two male header pins arranged beside each other, you can connect them using a dedicated "shunt" or "cap" connector. This can mean permanently pulling a pin to ground, activating a certain section of your board, or any number of other uses in a semi-permanent arrangement. These colored shunts look fun.
• Solder bridge: Design solder jumper pads into your PCB to allow changes with the addition of a bit of solder. While application is more work than the pin header method, it also doesn't add any extra components (and it does an excellent job of staying in place). Solder jumper connections can be designed as open until soldered, or bridged/closed until the connecting trace is cut. They can also have three (or more) pads for additional options.

• Zero-ohm resistor: If a solder jumper is too crude for your tastes/design (and a cap is too fancy), you can instead add in a so-called zero-ohm resistor. This component connects two pads when applied, with (theoretically) no additional resistance. You can also sub in a non-zero-ohm resistor as the connector, giving you additional circuit options.

Superfluous(?) example: Jumpers on JC Pro Macro II

While "superfluous jumpers" isn't exactly an argument for using them, perhaps this is still worth consideration. When I designed the JC Pro Macro II macropad, my idea was to allow the user to set the +/- orientation of the I2C connection pins with solder pads. This would allow someone to use two configurations of little .96" SSD1306 displays.

At the end of the day, this added labor to the overall job, and probably caused more confusion than solutions. In retrospect, I should have just wired it for the standard display that I was using and specified this in the documentation. At ~$3 each, reconfiguring solder bridges is hardly worth it.

I was going to use the press-on cap jumpers, which would have meant two more BOM items, but a friend of mine at Tampa Hackerspace introduced me to the concept of solder jumpers. This seemed good because it saved on BOM costs. OTOH, cap jumpers would have been much easier to switch around.

Jumper usage, like everything else in engineering, is all about tradeoffs! It's good to know your options. It's also good to know when to just go with a standard connection!

But why, jumper?

Previous section notwithstanding, jumpers can be very useful in a wide range of situations.

First, jumper wires. You can use these to route connections from point to point on a breadboard, dev board, or other devices. They are extremely versatile, but they're not really in the same class as cap/solder/resistor jumpers that are designed into a board for a specific purpose. Just keep some around to use on an ad hoc basis.

In the case of a pin header cap, your device may have different semi-permanent settings that are selectable by the end user. It seems like I recall setting these on an expansion board on my home PC and/or on machinery at some point in my career in manufacturing automation. In such applications, you might call them roughly equivalent to DIP switches.

As an example, Raspberry Pi uses a jumper for boot select in its RP2040 hardware design guide's minimal board example. OTOH, they switch to a button in the RP2350 guide, which is a more elegant, though slightly more complicated, solution.

When you're prototyping, solder jumpers can be a great way to test out optional functionality on your board. However, they're not nearly as convenient as header caps, so don't expect end users to get out their soldering irons to switch a setting or two (see 👆). Zero-ohm resistors have similar benefits to solder jumpers, but add an actual, verifiable component on your board. Also, the ability to sub in an X-ohm resistor here could be a huge benefit in some situations.

Jumpers: An excellent option when appropriate

At the end of the day, not every design will require the use of jumpers, and you'll need to weigh the design time and board space costs of using them versus leaving them off. However, using jumpers can let you test multiple design options on a single prototyping board, or open up different configurations to a product's end user.

So keep the jumper option ready to go in your mental toolbox. You'll certainly find some great uses for it if you design enough PCBs!

Thanks for reading!

Thanks for reading my PCB Friday column! I'm looking forward to sharing more PCB-related knowledge and insights here, and I hope you'll follow along for the journey. You can also find me on YouTube as Jeremy Cook DIY, read my semi-technical musings at TechAdjacent.io, or email me at hi@jeremyscook.com!

Note that any Amazon links are affiliate.