The MonkeyAltimeter is a pressure sensor altimeter utilizing the Bosch BMP085 or BMP180 I2C pressure sensor, an LCD display, and a simple user interface.

The pressure sensor provides altitude information at +/­ 3 feet from ­-2000 feet MSL to 30,080 MSL.

MonkeyAltimeter provides the following functions by way of a simple interface:

● Sea­level pressure adjustment (Kollsman Window)

● Altitude reach notification

● Altitude deviation alert

● Vertical Speed Indicator

● Cabin Temperature

Instructions

Parts list:

3.3V / 8MHz Arduino Pro Mini

BMP180 pressure sensor

16x2 (TWI 1602) LCD panel with I2C interface (lots on eBay!)

8mm red/amber/green LED (e.g. WP799SURKMGKW)

Rotary Bourns Encoder switch (e.g. PEC11R-4215F-S0024)

Slide switch (power)

Optional:

Integrated TP4056 USB lithium battery charger

~300mAh 1-cell (1S) lithium battery

WARNING: Check charge output current on battery charger. Some are preset at 1A which can cause fires with smaller 1S batteries. The common one on eBay requires a SMD resistor to be replaced to dial back the current. (http://www.electrodragon.com/w/TP4056_Lithium_Battery_Charging_Board_1A)

Optionally, this one from SparkFun is easily selectable (but doesn't readily fit the unit): https://www.sparkfun.com/products/12711?_ga=1.239961930.878323687.1435504106

Source code: (Requires Arduino IDE 1.6.5+)

https://github.com/phreakmonkey/MonkeyAltimeter

Notes:

• The SDA and SCL lines from the sensors go to pins A4 and A5, respectively. (Not labeled on schematic, since A4 and A5 are in the center of the board on most Pro Minis.)
A4 = SDA
A5 = SCL
• The Bosch pressure sensor has a max VIN rating of 3.6V. Don't connect it directly to the Pro Mini VCC if you're using the 5V/16MHz Pro Mini board! (Exception: If you're "underpowering" the 5V/16MHz board at < 4V, you can get away with this. Careful, though, as there's no 3.3V vreg to save you!)
• If you use the 32U4-based Pro Micro instead of the pro-mini, you'll have to change the code and pin assignments for the rotary encoder (in addition to using the correct I2C interface pins) See the comments in the source code.
• If you buy a "knockoff" 8MHz / 3.3V Pro Mini on eBay, be sure to make sure what you end up with is really the 3.3V variant and not the more common 5V / 16MHz variant before you wire the BMPxxx sensor to it! The easiest way to do this is to put 5V or more on the RAW pin and measure the resulting voltage on the "VCC" pin. If it's ~3.3V you're good. If it's ~4.7V then you have the wrong board.

Be sure to read the included PDF "Operation Guide" for tips on using it!