I don't want to fry my new Minimum OSD board but I also don't want to carry two batteries around. It appears that folks are frying their boards by not using two separate power sources. Is this correct? If so, maybe someone could explain to me why this is happening?
The OSD and MP will only tell me the status of one battery...unless I am missing something.
I understand that a separate battery source is beneficial for a clear video reception, however one could also use a filter system.
Any ideas ?
Thanks in advance for your help :)
Rick
Replies
My question is this, I have the digital and analog jumpers tied on my minim, so it gets its power from the APM telemetry side. I have the 12v+ wire removed from my Vin/Vout on the minim, with just the ground and video signal lines in place...
Can I power my APM power module AND my camera/vtx from the SAME battery.
Because the way I read this is I would need 3 batterys on board, 1 motor, 1 APM, 1 camera/vtx. Can someone clarify this for me! Thanks!
OK so the docs over on Google Code suggest either disabling the 12v regulator all together and only using the power off the telemetry. Or plug 12v to the camera and power/video in on the OSD and it's power out goes to the transmitter. What I did is that, except I run 12v directly from the power distro board to the transmitter and the camera/OSD via a Y harness, this way the transmitter gets straight power from the battery and the OSD/Cam gets straight power from the battery. Since everything is grounded and the wires are short, the picture quality seems as good as its gonna get. I don't see any issues with the voltage regulator on the 12v output side having nothing to power. The board boots up perfectly and everything seems to have plenty of power. So I guess this is a sort of 3rd option for wiring it up. I would be happy to contribute to the Wiki for the wiring options for the OSD.
This is very similar to how I had my previous quad setup. 1 battery pack, Skylark Tiny OSD III, KK 2.0 board, same 12v camera. I built a wiring harness to power everything and even when the battery drops to as low as 9v (3S) while flying, everything worked fine. I hope the Minimum OSD doesn't mind going that low. Even then I tend to never fly below 10 volts.
I know this doesn't answer the original question, but pending someone official saying this is a great alternative for wiring, I think it could be a good solution for this if you really wanna run one battery.
-- Jason
Vernon nailed it.
Seriously, grab a second power source, double check your wiring and you are good to go.
I have been using the board for ages and it is fantastic, but for the love of god check what you are doing.
Also you can very easily get a second battery voltage/current draw if you want, but this should be relatively unescissary, cameras/ VTx'x draw very little as far as current is concerned.
For example I can run a camera, mimOSD, and a 1.5W 1.3gh VTX for over an hour on a 3s 1100mah battery without a problem. Probobly longer but I have never bothered to test it.
To your second question, you CAN power both sides of the board, but if it is the same line as your main power sources I would STRONGLY advice against it. Broadly speaking this is a terrible idea. You have noise to think of, which has the potential to literally fry the board if you are doubling the input.
Ultimately I would wire the power to both the camera and the transmitter and then run a third connection from that union and connect it to the camera side of the board and then connect nothing to the transmitter side. Of course you should still run the standard video connection.
Doing this you are powering both, but you are also only powering the minim osd once, which will lead to much more predictable results.
hope this helps.
It seems like this questions has still not been definitively answered. Let's ignore the noise issue for a moment and focus specifically on the technical limitations (if any) of powering the video side of the OSD board from the same 3S source that's powering the APM via the power module (i.e. a single battery configuration).
Is there some explicit technical reason why this shouldn't be done? Is there a ground loop situation that's causing people to fry their OSD? Is this just an urban legend? :)
Let's be clear about this, the failures are usaually from a crap miswiring job or other obvious fault of the user. If you follow the directions with healthy dose of common sense, it goes a long way.
Here's the fundmental problem. The APM and it's IO pins (telemetry) are 5 volts. Most cameras and video TX are not 5 volts. This is why the OSD chip internally has separation between the logic and video sides with a higher voltage on the camera (video).
Obviously, from 4 motors, the main battery power is full of noise if trying to directly power a 12 volt rated camera (from the 3 cell 11.1 volts) that probably works between ~7-12 volts input and the same is true for most video TX. Again, a good, low dropout regulator or proper filter likely could provide clean power to the video side. You have to determine the power draw of both the camera and the video TX along with the OSD. I think it's more than 1 Amp or maybe close enough that say a 7808 (+8 volt) or 7809 (+9) volt regulator is going to run hot, maybe too hot. This pretty much means a custom switching regulator to give you a decent 9 volts or so, considering the battery may drop to 10 volts under load, only leaving 1 volt of headroom which isn't enough on the typical linear regulator even if it could safely handle the Amp or more of current draw. It's a tricky subject tand that's why the second battery is an easy solution for most and solves the problem.
Of course you understand the OSD only converts information present in the telemetry stream from the APM to display so the APM must be reading the battery voltage and then sending it to the OSD and this is why it only reads one battery because the firmware on the APM and the general setup only reads voltage on one battery. Thus, this is a non-trivial matter as code changes and interupt routines to measure voltage hurt performance of the main software loop at best, and that's if you understood the entire code and hardware system. Every time you go to write serial data out the telemetry port, that's yet another pause. That's just the physics of an 8 bit micro that can only do one thing at a time.
Again, let' just be clear, most failures are due to miswiring. Another thing is that the OSD chip does throw off some heat (must have an internal linear voltage regulator on the video side) and thus the higher voltage you feed it, the hotter it runs (common sense). Airflow (something people forget about in a foam plane or enclosed box) could contirbute to early failures on a 12 volt setup. I personally did bench testing at 9 volts and everything was very reasonable temp wise but remember the video TX really likes proper voltage (typically close to 12 volts). If you half the voltage you double the Amps to have the same power which begins to become impratical on those 1.5 watt video TX units ( if they would even work that way).
You asked a very valid question so please don't take my answer as being harsh. I'm just trying to get you to look at the entire system, and once you understand that, then the "why" is a little more obvious. We have many problems with noise from the motors, but also, many parts of the system work at different voltages and all draw enough power that simple voltage regulators are not the easy answer. Sometimes, that small second battery that eliminates the noise, is far easier to handle the weight penalty than engineering a custom multi-voltage setup just for video. It's also likely a cost factor too. Batteries are getting cheap, but by the time you build the filter, and/or regulator, test it, and work out the kinks, the other guy has been flying for months just using a second battery.