yikes, calibration and repeatability might be an issue.Why not a small balloon and a micro switch? Could be quite small and should be repeatable. Even an old film cassette with a balloon stretched over the mouth to operate a micro switch should work.
Called a free sample ... as cheap as it gets.looking for barometric sensor, cheap?
yikes, calibration and repeatability might be an issue.
but Hmmmmm. the super micri tiny exspensive devices are not much more than that, but with capacitor plates on eacy side of the balloon. I wonder if a balloon envelope stretched around a washer with copper foil on each side might be a cheap easy trick. then add circuit bits to make it readable on the adc or maybe as a freq.
I can see it now, testing by tying to a kite and stopping every 50 ft or so to let is log a somewhat stable altitude
that'll be the route to go if the free samples idea does not work out, unless someone points out something real clever.I like the design idea - Use the capacitance to alter the frequency of a 555 timer and read the output frequency with picaxe to get height.
As the story goes, the introduction of "pudding cups" (foil sealed plastic cups of individual servings) was a huge success. There was one problem, the shipments from California to the mid-west USA stores were arriving severely damaged and un-saleable.The 35mm film can & balloon trick reminds me of sea level sealed plastic soft drink & chippy packets I noted bulging at 2000m (~6000') when in Dharamsala (Indian Himalayan region).
you are right, we are wandering off the track here.There are already a wide range of off-the-shelf sensors available to meet your requirements and there seems little point in trying to ‘invent’ an alternative. If low cost pressure sensors appear too boring, why not use a magnetoresistive sensor to detect when the rocket has tipped over at apogee and then deploy the recovery chute? The signal conditioning required by this approach is almost identical to that required by a basic bridge type pressure sensor.
yeah, completely forgot that while responding to the DIY posts. is there a US distributor?What do you deem as cheap?
I gave you one suggestion back at post 3. cost AUD$13.
if it can fit on the 14m speed wont be an issue, this is a separate project, just need it to watch the rocket go up, notice when it starts to go down and send a high out to pop a parachute out. would be nice if I can also get it to pop a second shute once if falls below a certain height on the way down, but i'd like to get th basics down first.The 20M does not support I2C commands - The 20M being listed under READI2C in Manual 2 is a mistake.
All current PICAXE's can do bit-banged I2C however it can eat up a considerable amount of code space and I2C bus speed will be slower than using I2C commands.
ok, I was guessing it would work on the 14M, but I thought I'd let experts decide for meFor simple standalone projects like this, bit-bnged I2C should be feasible. The 08M is probably best becuse of its bi-directional I/O making everything simple. It is possible even with fixed inputs and outputs and the 14M may be able to utilise the bi-directionality of Port C.
Yes, Futurlec in the US at http://www.futurlec.comyeah, completely forgot that while responding to the DIY posts. is there a US distributor?
can the 14m do I2C intrefacing?
I've looked at MAD(magnetic apogee detection) and am worried if the rocket weathercocks. not worried a lot.I still think a magnetoresistive sensor would be the best choice for detecting apogee. This can be used to detect the change in the vertical component of the Earth’s magnetic field as the rocket tips over. The Honeywell HMC1051Z has the required sensitivity and comes in a SIL package. However, the bridge output is only a few mV and an instrumentation amplifier will be required to interface to the 14M analog input.
On a related topic, be careful about the way you trigger the chute deployment charge. Electrical igniters can take a hefty current (amps!) and my pull-down the PICAXE supply causing a reset. It’s probably better to provide the igniter with its own battery.