looking for barometric sensor, cheap?
- Thread starter tater1337
- Start date
Rocketry instrumentation article
The January issue of Nuts&Volts magazine had a PICAXE based model rocketry instrumentation article that used a Honywell 24PPC 2-15 PSI pressure sensor. This low cost ("~$20") device is available from Farnell Electronics and many other suppliers. The associated 3 volt circuitry described in the article is extreemly simple. Just one 8-pin instrumentation amplifier and three resistors gives you the gain and offset.
The January issue of Nuts&Volts magazine had a PICAXE based model rocketry instrumentation article that used a Honywell 24PPC 2-15 PSI pressure sensor. This low cost ("~$20") device is available from Farnell Electronics and many other suppliers. The associated 3 volt circuitry described in the article is extreemly simple. Just one 8-pin instrumentation amplifier and three resistors gives you the gain and offset.
westaust55
Moderator
What accuracy are you needing?
I am using the HopeRF HP03 series (mainly the HP03S but also have a HO03D both technically the same). Available at www.futurlec.com.au.
Operates at 3.3V, i2c interface, includes a temperature sensor as well.
I am using the HopeRF HP03 series (mainly the HP03S but also have a HO03D both technically the same). Available at www.futurlec.com.au.
Operates at 3.3V, i2c interface, includes a temperature sensor as well.
Rickharris
Senior Member
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.
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
Or, perhaps try some research using GPS /NMEA
height above MSL info?
$GPGGA
http://www.gpsinformation.org/dale/nmea.htm
The link could also be useful
for your other thread/question re. GPS info.
e
height above MSL info?
$GPGGA
http://www.gpsinformation.org/dale/nmea.htm
The link could also be useful
for your other thread/question re. GPS info.
e
Called a free sample ... as cheap as it gets.
Rickharris
Senior Member
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.
that'll be the route to go if the free samples idea does not work out, unless someone points out something real clever.
so, anyone know of any US suppliers who can supply evaluation samples?
Given that the "deployment of parachutes" need, the actual pressure needn't be too picky. So long as it actually opens (while falling!) the trigger height wouldn't be that critical. There may even be merit in delayed opening to minimise wind drift.
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).
Simple 555 type techniques may need to factor in the lower temps at altitude- such circuitry (including PICAXEs of course) can be quite sensitive to temp changes. Stan
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).
Simple 555 type techniques may need to factor in the lower temps at altitude- such circuitry (including PICAXEs of course) can be quite sensitive to temp changes. Stan
Last edited:
Mycroft2152
Senior Member
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.
It took a while, but someone finally realized when they were trucked over the Rocky Mountains, the drop in outside air pressure caused them to blow the tops.
Solution - stronger glue.
It also depends if repeatable altitude is required or simply high or low. If you want to have the device activated at the same altitude each time, you need to recalibrate each time used to allow for different atmospheric pressure. This may simply involve opening both sides of the sensor to atmosphere then using the difference to determine altitude. To select a particular altitude investigate the fairly linear change in pressure for change in altitude.
The suggestion of using a 555 and using metal plates as capacitors appears to me unlikely to work due to the very low capacitance between relatively small plates relatively far apart. It would at a guess be in the order of nanoF's.
Fred
The suggestion of using a 555 and using metal plates as capacitors appears to me unlikely to work due to the very low capacitance between relatively small plates relatively far apart. It would at a guess be in the order of nanoF's.
Fred
Yet another 'wheel'.
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.
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.
westaust55
Moderator
What do you deem as cheap?
I gave you one suggestion back at post 3. cost AUD$13.
I gave you one suggestion back at post 3. cost AUD$13.
yeah, completely forgot that while responding to the DIY posts. is there a US distributor?
can the 14m do I2C intrefacing?
BeanieBots
Moderator
Only 'X' parts support I2C.
(though there seems to be a little confusion in the latest manual about the 20M. Read but not write
)
(though there seems to be a little confusion in the latest manual about the 20M. Read but not write
)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.
hippy
Ex-Staff (retired)
For 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.
ok, I was guessing it would work on the 14M, but I thought I'd let experts decide for me
Now, I just found the US source for them, so I should be good to go come payday when I can order. can anyone point me to some i2c bit banging code to look at?
westaust55
Moderator
Yes, Futurlec in the US at http://www.futurlec.com
Do a search on HP03 and they are there at US$9-90 each.
Maybe missed, but had not see in your prior posts for this thread any reference to a particular PICAXE mentioned.
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.
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.
I've looked at MAD(magnetic apogee detection) and am worried if the rocket weathercocks. not worried a lot.
accelrometers are another thing we are looking at, including 3 axis for gyro systems.
the deployment will come off the 12volt 7ah battery, I'll be doing ground tests to make sure the 7805 keeps its share of the juice (diode + filter cap if needed)
for some reason the futurlec website wond let me order, sent em an email, went to the hope website and requested samples too.
still haven't done the "first" project yet (i.e. blinking diode) still too busy watching the servos play