SparkFun Forums

[corvette123]

i havent tried this one out yet.

but i am!

i needed a pressure sensor that can go from sea level to 100K feet and the scp1000 doesnt do that.

this one has 10 Pa (0.1 mbar resolution) and is digital spi.

and it goes to about 1Kpa (10mbar) which is a bit over 100K feet using the standard sea level.......

digikey stocks them!!!

im gonna try one.

http://search.digikey.com/scripts/DkSea ... -1098-1-ND


great for those Near Space balloon projects!

[corvette123]

it would be great if sparkfun does a bulk buy on these and the bosch pressure sensors!!!


with the 2 sensors i have posted and the scp1000, then you really have a sensor for any application and budget range.

[corvette123]

remmeber the scp100 is only quoted in the data sheet to about 30K feet...

now looking at this datasheet, it does require a little more processing as you have to run the temperature comp equations yourself hahahahah....

but its worth it....

it also does need a 32.768 clock.


refresh rate is approx 15 hz.

so yah it has some ugly things...

but its still a nice chip.

if sparkfun buys them, then breakout board for 20 bux.....

so please buy em sparkfun!! these are worth it.

[gussy]

I was looking for something like this (for an actual aviation altimeter) a few weeks back. The SCP1000 is nice, but not quite fast or accurate enough I don't think.

I looked at the link, haha wow that's a blast from the past!! I actually have one of these, I bought it about 3 years ago for a project it never got used in.

These are cheaper than SCP1000's as well, but like you say they are a bit more complicated.

The 32.768khz clock is what put me off them. Plus they are a bit more *raw*.
I never got to writing an interface for them but apparently its a bit of a hacked together SPI interface from what I found.

I would be interested to see what you find in your tests.

I think after this option I may start looking at an analog pressure sensor and a 24bit AD converter for what I need. Know of any with small footprints?

Edit:
I was always under the impression that this was more accurate than the SCP1000. It seems that isn't the case?
SCP1000 has a resolution of 1.5pa and the MS5540 has a resolution of 10pa.
If this is really the case I don't think the MS5540 is worth the hassle (unless you want to go really high like you do).
In quantity the SCP1000 is cheaper.

I still need to get around to testing that BMP085...

I need something with 1m resolution and 11,000m ceiling for my application. I think the SCP1000 will do the job. Any thoughts?

[corvette123]

yah it does suck that theres no CS line...

however we are using it in a dsPIC with 2 SPI modules so it gets its own module no problem.

yes the compensation routines have to be run on the host uC.... no problem for us... since we are doing tons of stuff in DMA we have the MIPS leftover hehehehe...

and yes the 32.768k clock it needs, it likes a square wave... but waves.... i think i can get away with a regular oscillator sin right into the pin...

i put it into a schematic today without really testing it out....

the documentation is pretty straightforward.

i dont see any possible surprises happening.

basically we needed one that could go over 100K feet and the SCP1000 only does like 30K feet (it may do higher but at grosser errors? i havent tried...)

comparing the 2,

the MC5540C beats the SCP1000 hands down in altitude, and depth!!! yes thats right, they use variations of these for depth sensors too.

SCP1000 beats in resolution, but they are about even at 10 Pa accuracy after software fun.....

I do like the SCP1000.... but the specs of this project just make it the wrong choice.

yah speed wise its about 15 HZ...... slower than SCP1000.

so i guess it simply falls into the class of pressure ranges.... when u need to take a wider range of pressure than the others can handle.


have you seen any other pressure sensor that can do 10 Pa with this wide a range of pressure? from sea level to past 100K feet?

the freescale stuff which people commonly use are rated 1.5% FS error (which sucks) down to about 115Kpa to 15 Kpa..

yah ive been looking

but anywhoo.... with our 1st prototype (and our first near space balloon) will let you all know how it goes....

of course u can always follow on our site.

and we will be selling the Near Space Telemetry controllers as well.

[corvette123]

for your application i think the bosch sensor can do it with some software filtering.... of course thats not knowing the "vehicle" its in and how fast it could climb / descend.....

if its a hobbyist design, then id go with the SCP1000.

if its a commercial design / mass production then id make the bosch work.

[gussy]

It's a semi-commercial altimeter for ultralights that I am researching and thinking about constructing.

Why do you say the Bosch would be better? Only $5 difference in price at quantity (from memory).

[corvette123]

for commercial product $5 bucks difference ?



if the bosch works, then its a no brainer.

[gussy]

$5 is nothing in the BOM when a device would sell for at least a few hundred $$...

Then again if I was making 100's or 1000's it might be a different story.

[corvette123]

if a cheaper one can do the job for commercial, then 5 bux is 5 bux.



it adds up mighty quick.

[gussy]

Depends if the difference it makes is worth $5 I guess.

I wonder if you can get <1m resolution from the Bosch.

[ohararp]

Walter, you might find this wiki I did helpful.
http://www.sfcompiler.co.uk/wiki/pmwiki ... er.MS5540C

Overall the chip is pretty awesome. You do need a 32KHz oscillator though and they can be a bit expensive.

[corvette123]

i think you can get that accuracy with software filtering on the bosch... but yah u just need to buy one and test errrr out

ohararp:

tnx for the link, swordfish! forgot about that compiler

yah you could use PWM....for the clock... we are using the dsPIC so we have the very easy to use OC lines which can work off timer 2 or 3 however i have those 2 timers in use for ....other things....

so yah had to go with an external 32.768 osc.

[corvette123]

ahhh thats your swordfish module

are you guys selling those?

would be a nice product for you, i havent seen any breakout boards for that sensor as of yet....

[ohararp]

I have a couple of those boards still, no parts, if you are interested in one drop me a line.