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PCF8574 pins have no direction register. A pin becomes usable as an input when its output latch holds 1, and a port read also clears its interrupt condition.
PCF8574 Inputs: Write High First, Then Read the Port Read More
MCP23017 interrupt service is mostly a register-order problem: find the flagged pin in INTF before reading INTCAP or GPIO clears the condition.
MCP23017 Interrupts: Read INTF Before INTCAP Clears the Event Read More
The HC-SR04 can accept a 3.3 V trigger, but its Echo output is 5 V logic. Two 10 kΩ resistors make the basic interface safe and predictable.
HC-SR04 Echo Is 5 V: Divide It Before a 3.3 V GPIO Read More
The ACS72981 carrier’s direction, supply and current range determine zero-current voltage, sensitivity and how much of an ADC’s input span is actually usable.
Choose the ACS72981 Range Before You Wire Its ADC Output Read More
Convert a hotend’s mm³/s limit into a realistic motion speed using extrusion cross-section, then verify which slicer limit is actually active.
3D-Printer Speed Is Capped by Volumetric Flow, Not the Headline Number Read More
A 5 V UART TX can overstress a 3.3 V-only RX input. Translate each direction from the receiving pin’s limits, then verify thresholds and edge shape.
5 V UART Into a 3.3 V MCU? Shift the Receive Path, Then Check the Return Read More
A USB-powered board can work through an A-to-C cable yet stay dead on a C-to-C supply when its receptacle lacks the required Rd pull-down on both CC1 and CC2.
USB-C Board Works With A-to-C but Not C-to-C? Check Both CC Pull-Downs Read More
The Raspberry Pi Debug Probe exposes separate UART and SWD paths. UART shows serial output; SWD plus OpenOCD and GDB can halt, inspect, step and program an Arm target.
Raspberry Pi Debug Probe: Use UART for Logs and SWD for Halt-and-Step Debugging Read More
A TCA9548A does not renumber identical I²C sensors. Its control byte connects selected downstream branches, and reset returns every channel to off.
TCA9548A Channel Selection: One Control Byte Is the Difference Between Sensors Read More
BMP390 altitude is calculated from a pressure ratio, so a stale sea-level reference can move the reported height while the raw sensor pressure remains stable.
BMP390 Altitude Drift: Calibrate Sea-Level Pressure Before Blaming the Sensor Read More