Datasheet https://raw.githubusercontent.com/DFRobot/Wiki/SEN0290/DFRobot_SEN0290/res/Coilcraft%20MA5532-AE.pdf https://raw.githubusercontent.com/DFRobot/Wiki/master/SEN0290/res/SEN0290%20(V1.0)%20Schematic.pdf AS3935 Chip available at Digikey and Mouser, not any other normal distributors. https://www.coilcraft.com/en-us/products/rf/rfid-transponders/x-y-axis-transponder-coil-2mhz/ma5532/

Antenna from coilcraft: 1 1.47€ 100 1.26€ 250 1.01€ 500 0.93€ 1000 0.73€

I2C Chip contains 10k pullup on SDA but not SCL. Addresses 1, 2, or 3, depending on config pins.

ab max power 0.1 mW Normal listening mode: 70 μA Signal processing mode (for 1 to 1.5 secs after squelch opens): 350 µA

Receiver centred on 500kHz, bandwidth 33kHz.

The shortest time span between two lightning strikes that the AS3935 can resolve is approximately one second.

“Disturber” means QRM.

Antenna LC oscillator needs to be 500kHz +/- 3.5%. Can be calibrated by setting trimming capacitors according to timing signal on IRQ pin.

A badly designed, pulled, aged, uncompensated crystal oscillator might be 50ppm off, so much better than needed as a calibration standard for this application. Therefore can use a µC to calibrate it automatically. I don't see this done in the Sparkfun library even though it seems obvious.

The chip can the calibrate its clocks from the above value, so antenna should be trimmed first. Clocks calibration must be repeated after power loss.

Gain: two ranges for indoor or outdoor, and then configured levels in range.

Input is compared against the watchdog level. A squelch, I would call that. Also compared to a configurable noise floor level. If exceeded, interrupt warning sensor won't work.

When squelch opened, an interrupt is generated and signal is classified. It can be Lightning or QRM. If lightning, energy and distance estimations are made. Distance depends on previous detections too. The chip has a memory.

Interrupt 0 means distance estimation changed.

Usage procedure Trim antenna frequency. Calibrate internal clocks. Set gain: indoor/outdoor and level. Indoor/outdoor refers to setting of AFE_GB - Analogue front end gain boost. Set max noise floor. Set watchdog level (squelch). Set any more detection levels you want.