The features of the device would be:
- Low cost, ideally less than $US50 in components per device for the production of ten prototypes.
- Simple electronics with the bare minimum of components:
- A digital pressure sensor module - easy to interface with a micro controller with I2C or SPI interface.
- A micro controller IC - cheap, must have free C compiler available and offer lots of ports.
- A bluetooth transmitter module that uses the Simple Port Protocol for easy access on the target device.
- Voltage regulator IC - something efficient and not electrically noisy.
- LiPo battery, ideally one from a mobile phone so it is easy to source. I want to be able to use the device for at least 20 hours without recharging.
- Recharge circuitry that allows recharge from a USB port.
- Surface mount resistors and capacitors.
- Small circuit board.
- Case, ideally starting with an existing case design
- A few LED's for indicating connection status
- One button (on/off)
- It should spit out pressure data often enough to enable an Android vario app at least as capable as commercial varios.
I wanted this device and app not just for me, but for the broader flying community. This means that I planned to do the following:
- Provide this blog, so other pilots could get their geek on.
- Make the vario software open source with something like the LGPL licence, so anyone could copy it and use it for anything. I do not intend to sell the app, it will be free.
- Make the bluetooth data stream format open so that other developers can make apps, either using my basic vario app as a reference or make their own app.
- Provide enough info so others could replicate the hardware development. However, I intend to produce the bluetooth devices in limited quantities and sell them for less than $100 each, enough to cover costs of components and production.