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My idea is to record the acceleration/altitude of a small model rocket launch using these sensors and record all the data onto a microSD card which I'll retrieve afterwards. I'd like to be able to plot all of the data to analyze the performance of the rocket. This data will also help compare the experimental results to the theoretical ones.

Accelerometer

OpenLog/SD Card

(Was only allowed two links so couldn't include barometer)

I have a few questions to make sure that my logic is sound when trying to design this circuit;

1.) Since the OpenLog contains the ATmega328 microcontroller I was going to use the Arduino to write the instructions to this which will initialize the two sensors and start logging data. Is this the correct way to do this? From what I could tell the other sensors did not contain any EEPROM/Flash so there was no way to store any code on there.

2.) If I have multiple sensors running at the same time is this going to cause a data conflict when writing to the SD card? Would it be possible to save two different .txt files, one for each sensor?

Thanks

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  • Model rocket flights are short enough you might consider an SPI flash instead of a micro SD card. Write time will likely be a lot more deterministic. Given that most model rockets are small, you would ideally use a thin purpose-made board having exactly the components you need, for minimum weight. Another option could be to re-use the board from a tiny quadcopter, since that has a microcontroller and an 6-axis accelerometer, and solder a tiny SPI flash to it with flying leads. Or try to send the data over its 2.4 GHz radio, which can transmit as well as receive...
    – Chris Stratton
    Commented Oct 3, 2015 at 21:54
  • One thing about determining heigth. An accelerometer will not give you the exact height as far as I know. You can estimate the height by checking the acceleration but it won't be very accurate.
    – aaa
    Commented Nov 2, 2015 at 22:18
  • Not what you asked, but check if that accelerometer range is big enough for your rocket application.
    – Wirewrap
    Commented May 31, 2016 at 19:07

1 Answer 1

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The OpenLogger was designed to be paired with and Arduino Pro or Arduino Pro Mini and just log the serial output from one of those. You could theoretically use the OpenLogger itself to do the sensor reading and writing, however, the I2C pins that your sensor needs haven't been broken out on the OpenLogger.

This means if you really wanted to make this happen, you would have to hand solder those pins and break them out yourself. After that the process is pretty straightforward. SparkFun provides both the source code and directions on programming it.

If trying to break those out is a little too tricky, you can either pair it with one of those Arduino models and use it to read the data, or find another similar logger device that has more pins broken out.

Two answer the second part of your question, reading multiple sensors isn't a problem. Usually the way these sensors work is you send a request for data to them and they return the reading, so you would just request from the first sensor, request from the second sensor, write out to the file.

You can write to two different files no problem eiteher. I would not however, recommend writing to two different files. Switching from one file to another, back and forth introduces a little extra overhead which will slow down your loop. In rocketry, things happen very fast, and you'll probably want keep your loop running as fast as possible. I would recommend just writing to a single file and include data from both sensors probably something along the lines of time,accelX,accelY,accelZ,bar.

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  • Thanks for the help, glad I'm somewhat on the right track. Could you elaborate what you mean by breaking out the pins? Do you mean that I would need to wire the sensors up individually to the components on the OpenLog board such as the ATMEGA328 chip or SDsocket? Would I not be able to wire it using the predetermined pins that were labeled on board? I considered using an Arduino but my concern was that it wold be too big to fit inside a rocket. Maybe I could try to find a 'Mini Microcontroller'.
    – Horsejuice
    Commented Aug 4, 2015 at 22:00
  • To use the open logger you would have to wire it straight to the pins on the chip. If you look at this picture you'll see that not all of them have trace coming out from them (and some of those pins are the ones you need). There are plenty of options for small arduino compatible boards: Arduino Micro, Adafruit Trinket Pro, Sparkfun Pro Micro to name a few, Then all you would need to do is wire in a micro sd breakout like this.
    – Jake C
    Commented Aug 4, 2015 at 23:28

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