I am building an Arduino based airship and I need a way to find it's altitude using some kind of sensor, the altitude is going to be relatively low so I need something somewhat accurate and preferably cheap. Can anybody recommend an altitude sensor?
Simply use Ir sensors?
Definition of "relatively low" please
Are you talking about feet, 10s of feet or 100s of feet etc (or metres if you wish)
How about using an ultrasonic distance measuring device and hacking into the electronics.
Or even simpler, use something like this http://www.maxbotix.com/Ultrasonic_Sensors/High_Resolution_Sensors.htm?gclid=CMebi5nW5rECFQFItAodDn0ARA
My definition of low is 0 to 50ft so I need something accurate within a foot or two. and I was also hoping for a sensor that didn't need to be facing the ground to function.
Well that leaves you two options
a) measure atmospheric pressure having first accurately determined a zero height reference pressure
b) point sensor to Alpha Centauri and mesure distance from there
Neither of which will give you an accurate altitude
Just out of interest, what exactly is the problem with a sensor "looking" down. You say you wish to measure altitude so by definition the reference point must be the ground under your craft.
Just out of interest, what exactly is the problem with a sensor "looking" down. You say you wish to measure altitude so by definition the reference point must be the ground under your craft.
the craft has a tendency to roll. Atmospheric pressure should work fine as I can set the reference to zero before takeoff.
Your requirements are actually pretty hard to meet with inexpensive sensors. Barometric pressure is pretty simple but readings can change quickly with a gust of wind or changing atmospherics. GPS has altitude capabilities but I've read they are not very accurate or even repeatable. What do real aircraft use. Well barometric for general purpose 'we are high in the sky stuff', but the terrain following stuff, nap of the earth, needs ground mapping radar I believe, not cheap. I thinking something 'looking down' is about all you can work with.
Lefty
If roll is the problem then use at least 2 sensors both looking down but offset from the vertical by one half of their lobe diagrams. You will need sensors that offer lobes that are equivalent to your roll angle. Each being offset to the opposite sides of the vertical. Their combined lobe diagram will hence be twice that of a single unit. Then have your system calculate which gives the lesser height - this will be the "true" height.