I’m trying to make an altimeter recorder for a model rocket. My brand new MPL3115A2 sensor is giving un-useable data, so as far as I can tell I either received a bad sensor and would like to ask for a new one, or there’s something wrong with my setup.
I started this project 2 months ago with two MPL3115A2 SparkFun sensors, but their outputs drifted so much that they were un-useable. One was exposed to 5V, the other was in storage a long time, so I thought maybe I had damaged them. Here is the thread where I requested help with that. (viewtopic.php?f=74&p=216413&t=53015&sid … 864eabb8b6)
My project was constructed to fit a SparkFun sensor, so I ordered a 3rd one on 6/26/2020. It came, I soldered on header pins, and plugged it in. Unfortunately this brand new one gives un-useable data as well. Here is a graph of the output of the brand new sensor over a 7 hour period. You can see at the start that the output varies by just under 20 feet in the first 4 minutes.
I also purchased an MPL3115A2 sensor from Adafruit and I ran it at the same time as my brand new SparkFun sensor. Here is the data from that test. You can see that the Adafruit sensor is much more consistent.
I would be happy if the problem is in my setup rather than the SparkFun chip. Here’s my hastily sketched circuit diagram. It uses an Arduino Pro Mini 3.3v. I haven’t had any trouble with the OpenLog, or getting readings from the MPL3115A2 sensor, also the temperature reads just fine too.
Actual photo
Those sensors use barometric pressure to determine Altitude. Any change in pressure can affect the altitude readings. They’re calibrated in the factory with a reference point of a vaccum. So the environment and weather can really affect these modules. What you need to do is run reference data from local data (weather channel, known altitude, etc) and use that to offset and calibrate your data. The modules seem to be functioning correctly.
I’m new at this, but is it really normal for a sensor reading to change 80 feet in 5 minutes when sitting at rest inside a house?
In the SparkFun vs. Adafruit graph both sensors were running at the exact same time. If it was a matter of calibration, shouldn’t the output from both sensors at least show the same positive or negative slope at the same times? Both boards are built around the same MPL3115A2 IC chip, so even if calibrated differently they should both show altitude increasing when pressure falls and vice versa. The 2 graphs should track each other, but as you can see they don’t. (And for the record, both sensors were sitting within a few inches of each other in my basement, unmoving)
Do I have a defective sensor? A similar complaint was made in the comments section for this sensor. See comment labeled, “Works Fine, A bit of a ALT issue.” in the comments section here https://www.sparkfun.com/products/11084
Was that issue solved?
I tried calibrating the sensor but had no luck (see next paragraph). Could I please get a reply from someone at SparkFun Tech Support? It’s been more than 3 days since I last posted. Is there something I’m doing wrong?
I tried calibrating the sensor using this library I found on GitHub https://github.com/mariocannistra/MPL3115A2
I found my elevation using USGS and entered that into the barometer_calibration sketch (312.54 meters per USGS). But when I run that sketch, it tells me my altitude correctly for 20 seconds and then just gives me a temperature and pressure of -999.0
Help please?
This forum is not the correct place to request a product return. Start here: https://www.sparkfun.com/support
