Wanted to have a self powered telemetry pack in order to save up the battery of my tablet.
So I tried this:
Hooked up the 3DR radio to a 2S lipo via a ubec.
This pack is then to be fixed to the back of the tablet.
The battery leads are external for charging purposes.
The ubec is to be changed by one with a build in lipo alarm.
This is still a work in progress and requires some fine tuning :-)
Comments
Hi Arthur,
Most android tablets will not charge from the USB connector when the device is operating in host mode (and some can be damaged). I agree though, if a DC jack is available then charging the tablet is a great idea.
Why not power the tablet with the battery?
My tablet can charge through USB and a DC barrel jack. Charging the Tablet will give energy to DroidPlanner and the 3DR radio.
If you don't need the high discharge rate and are worried about over charging/discharging, you could simply solder a couple cell phone batteries together. They've got their protection circuits neatly integrated. I use this method all the time.
If the 3DR radio's regulator is a low dropout regulator, you could theoretically just run them off one cell with no UBEC or step-up in between. Is that logic sound? Correct me if it isn't :)
Personally, I'd rather have the radio run off the tablets, unless you know your radio battery is going to outlast your tablet's battery. I'd hate to have my radio die out on me without knowing it. I'd at least you'd know your complete system's battery status running off your tablet.
I have a spare 350mah 2S lipo, how long do you thing it can run telemetry?
How about a single cell lipo (no balancing) with a 5v booster? Sparkfun even makes one with a built in charge (usb or another source) https://www.sparkfun.com/products/11231
I've been looking into this for my Tablet because I run my rover off a Wifi Link and when my tablet gets low on batteries the telemetry link gets weaker and the video and photo quality goes down with the battery power. Please keep us posted on this project of yours! I'm sure many of us here can find great use for what you're working on!
Thank you Jan!
Thought on the NiMh but then the box becomes a little bigger as well.
I have to admit it is less complex as a lipo and better to integrate (use of a jack).
@Jasja
4.8V should be sufficient as the 3DR radio module itself is powered on 3.3V.
There is a voltage regulator on the circuit board that reduces the 5V from the USB to the required 3.3V.
I don't know precise what is the allowed voltage drop (probably 1.25V) so with 4.8V you are still in the clear.
If you do, you'd need 4x 1.2V -> 4.8 volt, is that sufficient? - Thanks,
Nice idea. But I'd suggest using NiMh batteries instead. There's not need for the complexity of LiPo in this application. Worrying about balancing, overcharging, overdischarging storage charges, etc. Since power density isn't a big deal in this application, simple NiMh makes more sense I think.
Just provide a jack for a trickle charger in the case. Plug it in when you get home. Unplug it when you head to the field. Easy peasy.
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