Six electronics experiments

Campaigns81–86: complete source programs, blank observation worksheets and editable original SVG/PNG diagrams. Host/model checks do not establish physical measurements or target execution.

1. 81 — TLC5916: A Constant-Current LED Driver Still Needs Voltage Headroom
2. 82 — PCF8574: Reading a LOW Pin Must Not Turn an Input Into a LOW Output
3. 83 — SN74AHC123A: A Retriggerable One-Shot Can Notice a Missing Pulse
4. 84 — ESP32 BLE Beacon: A Fresh Advertisement Can Contain an Old Observation
5. 85 — ATtiny85 ADC Noise Reduction: Capture First, Read the Histogram Later
6. 86 — UNO Optocoupled Pulses: Isolation Does Not Preserve Every Edge