The pull-up jumper

What the strip does

The pull-ups on SDA and SCL do not go straight to VCC. They meet at one pad on the back of the board, and a strip of copper about half a millimetre wide joins that pad to VCC. With the strip, both pull-ups are connected. Cut it, and both come off together.

Every I2C bus needs pull-ups somewhere, and only somewhere: one pair would do for the whole bus. Blocks bring their own so that each works alone. The jumper is for when several are on one bus and there are more than you want.

How many is too many

Add blocks and watch the rise time. Each block's pair of 10 kΩ joins the others in parallel, so the resistance falls and the lines rise faster. That is the opposite of what most people expect from adding something to a bus.

The cost is current. Whoever pulls a line low has to sink everything the pull-ups supply, and I2C only promises 3 mA. At 5 V that is 1.7 kΩ, which is six of these boards in parallel. Short of that there is nothing to gain by cutting.

So: one to five blocks, leave it joined. Cut it when your bus already has strong pull-ups of its own, a few kilohms on another module, and you are adding the TK31 beside them. Never cut it when the TK31 is the only thing on the bus that has any.

If you cut it

Score across the strip with a craft knife and check with a multimeter that the two pads no longer beep. It is reversible: a blob of solder across the pads joins them again.

The rise-time numbers above are worked out from a formula, not measured, and the capacitance is a guess you move with the slider. A breadboard and a few jumper wires come to something like 100 pF.