The small bridge that shorts two neighbouring header pins — and thereby sets the operating mode on countless boards. It fits any pin header on the standard 2.54 mm pitch, so practically every development board, every shield and every module. Fitted means connected, removed means open; there is nothing in between. You choose the colour — and that is more than taste when several jumpers on one board do different things.

• 2.54 mmstandard pitch, 2 pins
• 6 coloursblue, yellow, green, red, black, white
• open or closedno intermediate state

What the jumper does

• A setting without software: what a jumper determines is fixed before the first instruction runs. That is exactly why start-up behaviour, addresses and enables hang on jumpers and not on configuration files — they take effect at the moment of switch-on.
• Visible rather than hidden: you can see on a board how it is set. For a device someone else picks up in two years’ time, that is the difference between understanding and guessing.
• Colour as an ordering system: six colours let you keep functions apart — red for supply, yellow for address bits, black for everything else. On a board with five jumpers that saves any labelling.
• It fits everywhere: 2.54 mm is the pitch on which pin headers, stripboards and breadboards are built. A jumper that fits here fits almost anywhere.
• Nothing that breaks: a plastic cap over a sprung metal socket, no mechanism, no wearing part. It outlives the device it sits in.

Where it is needed

• Setting start-up behaviour: programming or run mode on ESP and Arduino boards, boot source on single-board computers.
• Setting the I2C address: many sensor boards let their address be chosen with one or two jumpers — the precondition for putting two identical sensors on one bus.
• Switching in the termination resistor: on RS-485 and CAN, termination belongs only at the end of the run. A jumper makes a node either an intermediate or a final one.
• Choosing the supply path: USB or external power supply, 3.3 V or 5 V logic — on modules offering both, the jumper decides.
• Temporarily disabling a function: taking an LED, a buzzer or a pull-up out of play without soldering.
• Prototypes and fault finding: breaking a connection experimentally and restoring it, without altering the board.

That settles the selection. What follows is the depth for use.

Open does not mean “off”

A jumper makes a connection or it does not. What the board makes of that is its own business — and this is where the most common misconception sits. With the jumper fitted, the input is unambiguously at the connected level. With it removed, the input hangs in the air, unless the board provides a pull-up or pull-down resistor. Such an open input takes on no defined state but follows interference from its surroundings.

Well-designed boards have that resistor fitted, and then the simple rule applies: fitted is one level, open is the other. On a circuit of your own design it is easy to forget. If a jumper works sometimes and sometimes not, it is worth first looking at whether that resistor is there — and only then suspecting a poor contact.

Technical data

The general product data — colour and manufacturer — is in the detail table further down this page.

Scope of delivery

• 1 × jumper in the colour selected above

Help with the choice

Unsure which pins on your board need bridging? Send us a photo of the header and the name of the board — we will gladly help with the identification.