#nrf52.
Posts on the Alpisto engineering blog filed under#nrf52.
- 01#flybeeper#fanet-vario#sun-vario
The note that never sounds: what a piezo vario actually plays
Small varios beep in a way nobody would call pleasant, and it is not because nobody cared. A piezo disc is a bell with one note of its own, and a vario plays a tune on it by feeding it square waves and letting the bell pick what it likes. I put one in a desk drawer with a microphone: at 1000 Hz the note that was asked for comes out 33 dB below its own third harmonic, loudness swings 16 dB across the tone table, and the obvious way to soften a beep turns out to make it sharper.
17 min read - 02#flybeeper#sun-vario#variometer
Fourteen metres that were never there: a soldered barometer's thermal drift
Everyone who builds these devices knows you must not solder near the barometer, and that the third rework kills it. Nobody says by how much. This one came off the bench at 470 Pa/K against a rated 0.5, inventing 14.5 metres of climb while sitting still. Thirty lines of firmware removed 95 % of that and every bench test agreed — until somebody picked the device up and the vario went the wrong way. The number behind the folklore, and why the fix helps an altimeter and provably cannot help a variometer.
24 min read - 03#flybeeper#fanet#ads-l
Teaching a LoRa vario to hear ADS-L, and finding the time to do it
An ADS-L receiver must know when each UTC second starts, and receivers normally get that from GNSS. My vario has no GNSS on purpose: its position comes from the pilot's phone. So I took the time from the phone too, over Bluetooth, and measured how accurate that is. It is accurate enough, with room to spare: the share of frames the device caught went from 15 % to between 50 and 100 %.
19 min read - 04#flybeeper#sun-vario#variometer
Measuring a vario with a USB tester: 20 seconds per mode, and 420 µA that were never mine
I spent eight hours per data point measuring a solar variometer through its own capacitor. Then I measured the same device directly with a USB tester and got a full consumption curve in twelve minutes — along with a 420 µA floor that belonged to the cable, not the device. What both methods agree on, where they don't, and how to read a WITRN tester from Linux.
14 min read - 05#flybeeper#sun-vario#variometer
A 10-farad vario, measured: where every microamp goes
Eight hours of discharge logs on a solar variometer running off a 10 F lithium-ion capacitor. The current isn't constant, the buzzer isn't the main consumer, the barometer is — and the runtime formula that falls out of it. Plus what the enclosure had to become once the electronics stopped changing.
18 min read - 06#flybeeper#fanet-vario#fanet
See and be seen — a solar FANET vario you never have to charge
The FlyBeeper FANET Vario is a wireless, solar-powered FANET beacon and barometric variometer in one. No GPS inside — it reuses your phone's, works as a plain radio driven by the app, and puts you on the map for nearby pilots. Full app, BLE protocol and specs. A quiet pre-order at €149 with free shipping.
13 min read - 07#flybeeper#fanet#lora
FlyBeeper FANET: a Bluetooth Bridge to the FANET Radio Network
An always-on BLE bridge to the 868 MHz FANET data network. No on-board GPS — the smartphone provides position, the device just radiates. Solar-powered, years of standby, full radio configuration over GATT so apps can transmit FANET, ADS-L or anything else on the same radio.
6 min read - 08#flybeeper#tas#airspeed
FlyBeeper TAS: a Bluetooth True-Airspeed Sensor with a Purpose-Built Pitot Tube
A purpose-built BLE true-airspeed sensor for paragliders and hang gliders up to 103 km/h IAS. Custom CFD-designed pitot tube with a 4% correction coefficient versus 50% for hobby tubes, four PCB revisions ending in USB-C supercap charging, and standards-compliant BLE GATT services.
9 min read - 09#flybeeper#ps1#pressure-sensor
FlyBeeper Pressure Sensor: an Always-On Bluetooth Barometer for Flight Apps
An external BLE pressure sensor for paragliding flight apps like xcTrack and SeeYou Navigator. Always on, pair once and forget — wakes the moment the app subscribes to ESS pressure notifications. ±2 cm/s vertical-speed resolution from an SPL06, 5-year standby on a single CR2032.
5 min read - 10#flybeeper#rc4#remote-control
FlyBeeper Remote Control 4: a Bluetooth Four-Button Remote with Multi-Year Battery Life
An always-on four-button BLE remote for paragliding flight apps. No power switch, deep-sleep when idle, automatic wake when an app connects — battery life measured in years from a single CR2032. Built on Nordic nRF52, exposes the standard Automation IO Service.
3 min read - 11#flybeeper#mini-bt#variometer
FlyBeeper mini BT: a Tiny Bluetooth Variometer Built on Zephyr RTOS
A dwarf-sized BLE 5 variometer on nRF52 + Zephyr RTOS, exposing pressure, temperature, altitude, four-button remote and OTA updates through standards-compliant GATT services. The entire stack — GPIO, SPI, PWM, ADC, FLASH, OTA, DFU, BLE, GATT, plus the OS — fits in 200 kB.
18 min read