Hey Earl,
I have selected the Bosch BMP085 as the altimeter for my Pic32 based Autopilot.
It's the successor to the SMD500. It can be had for < $10 US from digikey.
I'll keep everybody posted over the next few weeks as I begin writing code. The only issue I see is a fair amount of math that needs to be done to linearize the data and convert it to Feet or Meters. I plan on doing that at a fairly low rate though since it's only for the benefit of human observers. Any control loops using the data will work off the raw data with appropriate gain terms applied.
Earl, you may want to try the BaroMod, same cost, but provides a linearized output, 0.25mV per foot, so you
don't have to do nasty math to get a real alt. In hardware, an anti-log amp, the correct voltage is output to your
a/d input. The atmosphere has a log pressure function, a bit hard to straighten out with bit banging in PICs , for sure.
* The BaroMod allows easy altitude measurement using any 0-5V analog electronics or embedded processor, with at least a 10 bit a/d converter.
* An anti-log amp is used to create a linear response. No complex software math is required to process sensor signal, freeing up computer for logging or telemetry tasks.
* Typical usage with 10 bit a/d will yield 20' measurement steps, good for general purpose application. Higher res is ok.
Size: 2.05" x 1.15" x 0.65"
Weight: 17 grams
DC Supply: 5V
Range: -500' below sea level to 20,000'
Output: 0-5V linear, proportional response, 0.25mV/ft.
Modes: absolute,differential (subtract ground reading)
Temperature Range: -40 to 200 deg. F
Typ. usage: Feeding to 10 bit a/d results in 20' increments
Replies
I have selected the Bosch BMP085 as the altimeter for my Pic32 based Autopilot.
It's the successor to the SMD500. It can be had for < $10 US from digikey.
I'll keep everybody posted over the next few weeks as I begin writing code. The only issue I see is a fair amount of math that needs to be done to linearize the data and convert it to Feet or Meters. I plan on doing that at a fairly low rate though since it's only for the benefit of human observers. Any control loops using the data will work off the raw data with appropriate gain terms applied.
Brian
don't have to do nasty math to get a real alt. In hardware, an anti-log amp, the correct voltage is output to your
a/d input. The atmosphere has a log pressure function, a bit hard to straighten out with bit banging in PICs , for sure.
I have resolved a couple feet with this unit.
Under products at:
http://www.transolve.com/Transolve/index.html
* The BaroMod allows easy altitude measurement using any 0-5V analog electronics or embedded processor, with at least a 10 bit a/d converter.
* An anti-log amp is used to create a linear response. No complex software math is required to process sensor signal, freeing up computer for logging or telemetry tasks.
* Typical usage with 10 bit a/d will yield 20' measurement steps, good for general purpose application. Higher res is ok.
Size: 2.05" x 1.15" x 0.65"
Weight: 17 grams
DC Supply: 5V
Range: -500' below sea level to 20,000'
Output: 0-5V linear, proportional response, 0.25mV/ft.
Modes: absolute,differential (subtract ground reading)
Temperature Range: -40 to 200 deg. F
Typ. usage: Feeding to 10 bit a/d results in 20' increments
Price - US$38 + $5 ship
http://dev.uavp.ch/read-only/wolferl/datasheets/SMD500.pdf
By the way, the I2C device address for SMD5000 is 0x77 or 0xEE/0xEF, depending on whether you are using 7 or 8 bit I2C addressing.