This is an improved version of the altimeter made in 2008. The sole hardware change is to substitute a Picaxe 14M2 for the 14M. This permits better software. It is used at home as a barometer, with readout in millibars ot inches of mercury then as an altimeter on trips. For this latter application, it is designed to operate from a car battery, and to measure that voltage. In both applications means are provided to set the offset, either sea-level barometric pressure or current altitude, respectively. The design uses the Freescale MPX4115A sensor. A biassed amplifier restricts the range to - 700 to 13000 feet, adequate for our trips on paved roads in the USA and Canada. The substitution of the M2 permits the better six-range approximation used on the Mobile Logger to convert pressure to altitude. The output of READADC10 is accumulated 12-17 times according to the range, and then an offset is deducted.
Provision is made for properly displaying altitude below sea level and when in adjustment mode. The display uses a MC14489 serial LCD controller. However, a military-surplus six-digit 7-segment incandescent display was used, which is clearly readable in full sun. This required isolating diodes in each segment and boosters for both the segment and digit drives. |
This is the front of the Altimeter: |
Here are the circuit diagrams |
Here is the altimeter code |