Special features

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Lightning alerts can warn you with different actions (i.e. sounds) about approaching thunderstorms. This feature is available since firmware version 6.0.

The alerts are based on the TOA lightning data from our servers. You can specify your desired parameters like minimum distance, stroke count and time period. These values will be checked by our servers by the remote configuration feature. If the alert conditions are true, then a desired action will be issued.

An action can be triggered by a lightning alert or by other events (see next sections). The action defines which alarm sound should be played or whether an output pin should be enabled. A user defined URL can be called, which can be used for own purposes. After an action has been issued, it can be ignored for a adjustable time. An action can also be used by different events.

The AS3935 is a new microchip from austriamicrosystems, which has some lightning detection technique inside. It has been designed for mobile devices, which can inform their users about regional lightning activity. The signals from lightning strokes are received by a tiny ferrite antenna, which is tuned to 500 kHz. Compared with our own powerful amplifier/controller combination, the AS3935 is very simple and cheap, but it can not be used for lightning locating. Complete PCBs with microchip and antenna are available from different distributors.

The AS3935 can be connected to our controller board via I2C bus with 5 wires. Almost every parameter can be adjusted in the web-interface. The calibration of the antenna is done automatically after boot and after each parameter change. Refer to the AS3935 datasheet for more information about the parameters. When the AS3935 detects lightning, different actions can be started, depending on lightning count and distance (see actions_and_alerts).

Some pins of the STM32F4-MCU can be used as user defined inputs or outputs.

If defined as an input, a rising and/or falling edge (configurable) can trigger an action (see 5.6.1). Additionally, an URL can be called. This URL will contain parameters with the time-stamp of the trigger derived from the GPS 1PPS timer. Thus, it is possible to use the inputs for high-precision timing measurements.

Outputs are configured in push-pull mode. Each output can drive currents up to 20mA. The summarized current of all outputs shouldn’t exceed 50mA. Please check the STM32F407 datasheet for more information! An output can be toggled by calling a dedicated URL of the web-interface. Outputs can also be triggered by actions (see 5.6.1). As an example, it is possible to let a LED blink on a lightning alerts.

The analogue user input is an optional feature, which has nothing to do with lightning detection. When enabled, you can measure DC voltages from -3 to 30V at the measuring point. You will see them on the web-interface below CPU temperature and on the LCD on the first page. The voltage range can be changed by replacing resistors R64 and R65 with other values. You also have to change those values in the settings section on the web-interface. The default values are 10kΩ for the serial resistor Rs (R65) and 1kΩ for the RGND (R64). If you enter 0 for the RGND, then original voltage on the ADC-input pin will be shown.

Please note, that only voltages with low impedance can be measured, i.e. voltages from a powersupply or from a battery. The STM32F4DISCOVERY has an additional 10k pull-up to 3V included, which cannot be changed. As the used CPU-pin is also dedicated for a special function on the STM32F4DISCOVERY, a green LED will light up there when low voltages are applied.