Arduino Variometer

Arduino variometer for those who fly RC Gliders, DLGs, and other motorized and non-motorized RC sailplanes, as well as ‘big brothers’ – ‘manned’ gliders and parachutes, indicating whether there is thermal or not, or better known as “vertical speed indicator“, or simple Vario (this one is simplified version, without any display):

No radio? Direct audio mode:

Someone contacted me and asked if it is possible to use this vario without need for RF chip – for direct use. Answer is yes. Simply by adding crude audio amplifier to passive buzzer, which is actually speaker (loudspeaker). Sorry for ugly drawing.


If you have small “magnetic” buzzer, as Banggood describes, and if it is passive, then capacitor is 100 nF (0.1 uF), because low frequency sounds will reproduce badly anyway of such small membrane of the speaker. If you use some bigger speaker, then consider to use 1 uF or more, the best value is 100 uF, but it is maybe overkill because any small loudspeaker that can fit in your hand has actually bad low tone reproduction. Passive buzzer on Banggood: BUZZER 1-5V

Alternative option is to use 1W GPS (General Purpose Speaker) on eBay: 1W GPS loudspeaker


If you are sure that output on pin PD2 (or just 2 on Arudino pro mini V3) will not remain HIGH or digital 1, then you can omit this capacitor. DO NOT attach directly loudspeaker on the PD2 pin, because it has very low impedance and can ruin your Arduino. Although there is overcurent protection, I will not gamble with that. If sound is too loud, then add 1-500 Ohm resistor in series with loudspeaker. This way it will save power if you have battery powered device.

Schematic, for those who are lazy to visit RCgroups forum: variometer Note that on MS5611, there are used only four wires of seven. That is because other three wires are used in the case of SPI connection instead I2C as is on this schematic. Those ‘extra’ three wires leave not connected (NC). Arduino sketch, hover with mouse over the top of the code, click on “copy”, then CTRL+C for copy to buffer, and CTRL+V to paste into your Arduino IDE:

Debug option: ‘Serial.println’

This code by default has excluded serial print of temperature and pressure. For testing and debug of variometer – your circuit on serial monitor, remove ‘//’ tags before command lines, highlighted yellow on this picture: Arduino sketch variometer This Variometer is intended for RC models, as is DLGs, where ‘downlink’ is provided by TX and RX on 433 MHz, but if you wish to hear sound directly – without the need to ‘broadcast’ radio signal on 433 MHz, you may add capacitor of say 100 nF (or more for better low frequency reproduction) between pin ‘D2’ on Arduino nano and the audio amplifier. This capacitor serve for galvanic deoupling for protection of Arduino and amplifier. Use small audio amlifier, something like this one: LM386 audio amplifier This amplifier is proven to work on low voltage, ranging from 4 to 12 Volts. The amplifier ($2.11 US): LM386 audio amplifier on Banggood Also, aside eBay -you may find other parts on Banggood. What is the difference – Banggood is more secure and reliable seller, unlike uncertain sellers on eBay (many sellers are okay, but this is a ‘gamble’ – sometimes frusttrating and wasting time).