I'm making a barebones flight logger for a model rocket. It's my first arduino and rocketry project, so I'm going to keep things simple. I've got an arduino nano, an accelerometer and a micro-SD card unit. So far I've rigged the sensor to the nano and managed to code a basic launch detection and sensor readout sketch. I'm not anticipating too much trouble adding the SD card reader (still in the mail...) and making it log measurements to a file.
What I'm currently wondering about is how I'm going to power the thing. As the flight will last for a very short time I don't need to run the system for long (let's say 15 minutes at most; including some set-up time to turn everything on and position the rocket/launch controllers)
I'm considering two C2032 button cells and looking for some advice on whether this is a good/dumb idea, how exactly to wire this up and would welcome any and all other tips and thoughts. Thanks!
I'm making a barebones flight logger for a model rocket. It's my first arduino and rocketry project, so I'm going to keep things simple. I've got an arduino nano, an accelerometer and a micro-SD card unit. So far I've rigged the sensor to the nano and managed to code a basic launch detection and sensor readout sketch. I'm not anticipating too much trouble adding the SD card reader (still in the mail...) and making it log measurements to a file.
What I'm currently wondering about is how I'm going to power the thing. As the flight will last for a very short time I don't need to run the system for long (let's say 15 minutes at most; including some set-up time to turn everything on and position the rocket/launch controllers)
I'm considering two C2032 button cells and looking for some advice on whether this is a good/dumb idea, how exactly to wire this up and would welcome any and all other tips and thoughts. Thanks!
Cheers,
Lorenzo
For a model rocket flight data recorder, as you said you don't need much run time, and of course mass is a premium.
A CR2032 and similar lithium coin cell produces around 3.2 to 3.6 volts (one cell) which may be enough. I would suggest trying your setup with one cell and see how long it runs (and if it works reliably).
As far as turning on the recorder before launch, how about providing external power from a larger battery at the launch pad with two tiny Molex pins that pull apart at launch.
Your recorder will be powered by the GSE (ground support equipment battery) and automatically switch to internal power at launch. If it works for NASA, it should work for you!
That external power source is a great idea. I haven't built a proper 'launch pad' yet but am now considering one that incorporates some sensors and a car battery for these purposes. Could probably make a nice 'launch detector' as well with some kind of pull-away cord. Probably not this time though (time is getting a bit short before launch day and it's gonna be real basic: just a single estes C motor with a kit rocket. The electronics are the focus here)
I've ordered a 10 pack of those batteries and will do some experimenting. Now I know that the nano can run at different voltages with a tradeoff in clock speed. Does the board handle this automatically or do I need to tell it that it should do this somehow? And can I wire the cell to the Vin / GND pins without other concerns? I'm finding a lot of stuff on the web about voltage regulators and instability, I don't think any of that that'll be an issue for my simple circuit, agreed?
lithium button cells will not work. They max out at a few milliamps and SDcards can use over 100mA.
Use 3 LR14's (alkaline 1.5 button cells) perhaps, or a small LiPo.
Oh snap, I hadn't considered that! And I was planning to write to the SD card pretty much constantly as the whole setup could disintegrate at any moment. Hmm.
I'm going to be a little stubborn and experiment with the CR2032's anyway (as I already have them) as soon as the card reader arrives, but at least will know what to expect.
As for small lipo, that was actually my preference initially but then I couldn't find an easy way to charge them, do you have any tips for that? It doesn't have to be integrated into the build.
Well that's certainly embarassing, thanks though! I think I read a sparkfun article on the battery with lots of cautions and warnings regarding how to integrate a charger with arduino that turned me off it (at least whilst 'keeping it simple').
So, report-back time! I got the Lipo batteries linked by MarkT and they performed very well. One cell combined with a 5V boost converter could power the logger for over half an hour and probably a lot longer (that's when I stopped testing because a flight would be over in less than 5 minutes).
Last weekend was launch day (it got postponed a few times due to weather), at the first try the battery leads got disconnected on ascent (I used prototyping male-female wire connectors that apparently aren't very good connections; the wires were still attached but making only intermittent connection screwing up the log). As a quick fix I stripped the leads and twisted the copper strand together just before the second launch and that worked well. Results: 12G max acceleration, approximate speed 300km/h with a peak altitude (est.) of 305m.
RocketLorenzo:
So, report-back time! I got the Lipo batteries linked by MarkT and they performed very well. One cell combined with a 5V boost converter could power the logger for over half an hour and probably a lot longer (that's when I stopped testing because a flight would be over in less than 5 minutes).
Last weekend was launch day (it got postponed a few times due to weather), at the first try the battery leads got disconnected on ascent (I used prototyping male-female wire connectors that apparently aren't very good connections; the wires were still attached but making only intermittent connection screwing up the log). As a quick fix I stripped the leads and twisted the copper strand together just before the second launch and that worked well. Results: 12G max acceleration, approximate speed 300km/h with a peak altitude (est.) of 305m.
