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Topic: Small arduino "standalone" (Read 1 time) previous topic - next topic



I'm building an logging altimeter/barometer with pyro outputs
(to deploy parachutes) for a rocket project, it will basically read
the sensors and write to some sort of persistent memory which I can
download to my computer later on to analyze. I will probably skip
the pyro part for version1.

I ordered two MPX550P Pressure sensors from Freescale, and I got a
12bit A/D from a good friend of mine, does it make sense to use the
12 bit A/D instead of the internal 10bit one?

Any pointers how to get the serial part up so I can talk to a computers
serial port in a standalone setup?

It would also be nice if I could program the Arduino from that serial

Any pointers, comments or suggestions are very welcome :)

MPX550P: http://www.freescale.com/files/sensors/doc/data_sheet/MPX5500.pdf
12bit AD ads7841: http://focus.ti.com/docs/prod/folders/print/ads7841.html


Mar 20, 2009, 12:30 am Last Edit: Mar 20, 2009, 12:31 am by etracer Reason: 1
Probably the simplest cheap solution for the serial connection is to simply use a MAX232 plus a few capacitors. Then you'll have a fully functional RS232 serial port you can connect to your PC (and program with assuming you've have a bootloader on your chip).

The internal vs. external ADC depends on whether you need the extra resolution vs. the complexity of adding the extra chip, interfacing, etc. Factoring in the noise you'll probably get from the pressure sensors the extra bits might be meaningless.


Mar 21, 2009, 08:18 pm Last Edit: Mar 21, 2009, 08:18 pm by lnxrkthkr Reason: 1
Hello again,

Here is my first try at eagle.

Does it look like it would work? Please comment...

Cheers, L


In the max232 section,
c4 should be between V- and ground, not V+ and ground.
If you've got the MAX232 sitting there anyway, you can use the spare receiver, the DTR line, and a 100nF cap to add diecimila style reset.
iDuino - MaxSerial - [url=http://spi


Spiffed, thanks! I will update the schematic.. The reset part would
be a very welcome feature...


You can play with it later, but almost all MAX232-like chips will work with 0.1uF caps for the charge-pump and storage caps (C1, C2, C4, and C8 in your schematic), if the smaller caps mean a change from electrolytic to ceramic you may actually see better performance out of the MAX232 due to the much lower ESR. Really though, modern MAX232 chips are pretty resilient, as long as you get the caps in there, they'll usually work.

The reset part would be a very welcome feature...

Take a look at the MaxSerial schematic for an idea of how this could be implemented.
iDuino - MaxSerial - [url=http://spi


Hello again, thanks for the info and the link, very helpful!

Time to bring out the breadboard! I received all the components

Cheers, L


I think I got the reset part right, I have also changed so that
C4 is connected to V- ground.

Did I get it right?

Cheers, L


Looks good, but:
  • You likely only need 1uF for C4, although 10 won't hurt.
  • You have a 470uF cap on the MPX5500 Vout. I assume that was cribbed from Figure-4 of the datasheet, in which case you need 470picofarad, not microfarad.
iDuino - MaxSerial - [url=http://spi


spiffed, great find! thanks!
I have started to build the circuit on breadboard, I will let you all know
how it goes. After that I will try to get a pcb-layout done, I probably need to shrink it a little more but now I got a good place to start.

Cheers, L

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