Firmware on a constrained Bluetooth Low Energy system-on-chip and its radio stack across several projects, including adding an I2C sensor to an existing device on a battery budget. On a coin-cell device the hard parts are power topology and keeping the link alive under the radio stack, where a blocking wait or a back-powering path silently costs battery life or drops the connection, with nothing in the logs to explain it.
The stated ask, in the sensor case, is add a humidity sensor. The real risk is two-part and both parts are topological. Parasitic back-powering of a power-gated sensor through shared I2C pull-ups on an always-on bus, so the sensor never actually turns off. And a blocking measurement wait that starves the radio stack and drops the link. Neither is fixed by choosing a lower-power part, because neither is about the part.
The reflex, and the fix.
Gate the sensor and cut the signal
It reads as the correct low-power move and it is what a datasheet-driven design produces.
Shared pull-ups back-power the gated sensor through the bus, so it keeps drawing, and a blocking read starves the radio stack and drops the connection. The gate looks right and does nothing.
Fix the topology
Pull-ups powered from the regulated rail, a non-blocking read so the radio stack is never starved, and a gating arrangement that actually isolates.
Negligible impact as a property of the circuit rather than a claim in a specification.
Treat it as a topology problem, because both failure modes are paths rather than parts.
Pull-ups from the regulated rail
Shared pull-ups on an always-on bus back-power a gated sensor. Powering them correctly is what makes the gate real.
A non-blocking read
A blocking measurement wait starves the radio stack and drops the link. The read is restructured so the stack is never held off.
Coin-cell budgeting as the design frame
A single sensor read costing roughly 0.04 microamp-hours against an 850 milliamp-hour coin cell is the concrete anchor that turns negligible impact from a promise into arithmetic.
Measured, not assumed
A precision power analyzer where a bench multimeter is blind, because the currents that matter here are below what ordinary instrumentation resolves.
A single headline number hides where a system fails. This work was scored on the dimensions that actually decide whether it holds in production, measured on real, held-out cases rather than the demo path.
Presented as a five-project matrix. Confirm whether these are distinct programs before presenting as multiple clients.
A design that gates the sensor, cuts the signal, claims negligible impact, and quietly drains the cell through the pull-ups while dropping connections under load.
Delivered firmware across a five-project matrix, with the back-powering and non-blocking-read analysis as the signal detail, and coin-cell arithmetic used to reframe negligible impact from a promise into a topology guarantee.
What it owns, and what it hands to a person.
The guarantee is about the topology as built. A later board revision that returns the pull-ups to the always-on rail reintroduces the same failure with no code change and no error, which is why the finding is stated as a topology rule rather than as a fixed defect.
When a specification promises negligible impact, ask what circuit makes it true. A promise about a component is not a guarantee about a system, and the difference is usually a path nobody drew.