Dytters (A.K.A Audible Altimeters) saved skydivers' lives for so many years. Now, Audible Abby will save them money, too.

Basic Dytters have four alarms, one on the way up, and three on the way down. In the plane ride up, skydivers need to know when it is 1500 feet so they can take off their seat belts in case there is an emergency and they need to exit promptly. Furthermore, the door will open in summer time for fresh cold air and allow low altitude skydivers to jump. That has to be done above 1500 feet and anyone with a parachute or attached to a tandem instructor need to take off seat belt prior to opening the door. The first free fall alarm tells the skydiver that social time is over and to quickly move away from other skydivers. The next alarm happens after the previous alarm separation to indicate it is parachute opening time. The third free fall alarm is the strongest one. You will not hear it if you are under a parachute, but you will if you are about to make the evening news. With low altitude and high speed, this alarm is the last call for immediate actions.
You can get yourself a Dytter for $238 here: http://www.chutingstar.com/skydive/solo-ii-audible-altimeter ... or you can continue reading.

Supplies

Arduino Pro Mini
BMP280
5 Volt battery
Buzzer
2N2222 Transistor
Switch

Step 1: Soldering the Parts

GND of Arduino Pro Mini needs to be connected to GND of BMP280, buzzer, and negative side of the battery. The positive side of the battery needs to be connected to one side of the switch. The other side of the switch needs to be connected to 5V pin of Arduino Pro Mini, BMP280, and the Collector of the transistor. The base of the transistor needs to be connected to D3 of Arduino Pro Mini. SDA and SCL of BMP280 need to be connected to A4 and A5 of Arduino Pro Mini.

Step 2: Programming Arduino Pro Mini

Use pins 11,12,13, and RST of Arduino Pro Mini

For more information on programming Arduino Pro Mini see this tutorial.

The code that needs to be uploaded is in Github.

Step 3: Putting It All Together

Find a case small enough to fit in the helmet, but large enough to contain all the parts. If you have access to 3D printer you can make a custom case.

Step 4: Take It to the Skies

The noise from free fall into the wind would make it very difficult to hear anything. That's why we adjusted alarm altitudes to demonstrate from the comfort of our elevator.