If your barometric sensor exposed on APM2.5?? Or you have tape/foam hack to cover it. Here is more elegant way to cover your baro nicely. On older APM2.0 baro sensor was covered with another PCB so it was not so exposed to wind blows and you got better altitude hold with it. On new APM2.5 board upper daughter board has been removed and barometric sensor is now fully exposed so it needs to be covered to avoid erroneous altitude readings.

We made custom APM2.5 Filter PCB for this purpose. It connects on both ISP pins on APM2.5 and foam on middle covers baro. There are additional +5V input provided on this board if you want to boost +5V system on your flight controller.

Ardupilot-Mega Wiki page has guide how to cover your baro but we were thinking that there has to be better ways than using tape and foam. Yes there are. 

Which one you prefer?

Filter PCB's are now available on jDrones store, 4.5 USD each. So grab one during your next order and you will get a lot more accurate altitude response from your APM2.5 boards. 

Jani / jDrones

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Comment by David Anders on November 14, 2012 at 11:43pm

Thanks Jani - sounds and looks like a good idea.  Can you tell us how much clearance there would be for the pins either side of the sensor? Looks like we couldn't use the 3 pin connectors and have to slot each wire through individually? 

And secondly, @Chris, I remember reading that you said (in August) there would be a cover for those of us with APM2.5 in September I think.  I know you've been busy, but has this progressed?

Whilst this is great for the baro sensor, my preference would be for a cover of all electronics.


Comment by Jean on November 14, 2012 at 11:51pm

I'm pretty new to this, so please forgive me if this is a stupid question, but is there any way to install the APM2.5 in an airtight fuselage?  I'm guessing the answer is no, because the sensor needs to measure the atmospheric pressure.  But what I am building is a tailsitter optimised for high-speed horizontal flight, and I want the fuselage to be full enclosed for aerodynamic efficiency.  Sorry if I'm hijacking this thread - I just thought this might be a good place to ask this question about the barometric sensor.

Comment by Jani Hirvinen on November 15, 2012 at 1:58am

@David, there is a lot of space on both sides and about the height. Well if you have RC connector on side pins and it's facing upwards it will be higher than area with filter PCB. Overall thickness is around 10mm with this PCB. Covering whole electronics is one way but it's not possible on every device. 

@J-B, On airplanes there are not so much problems with this as electronics is mostly inside on area where are no massive airflow. If you have direct airflow then it would be good to cover baro again. Mainly this is for people who are using multicopters and all electronics is rather exposed on those. Baro is really sensitive for direct windblows. 

And correct, having it fully air tight airframe is not a good idea as you need to know atmospheric pressure to measure your altitude. So there needs to be at least small holes on airframe, box or where ever your electronics is. 


Comment by Jean on November 15, 2012 at 2:45am

Thank you, Jani.  Is it possible to connect an external barometric sensor to the APM2.5?  If so, I could just mount the baro sensor outside the enclosed fuselage.

Comment by Jani Hirvinen on November 15, 2012 at 3:08am

Basically yes at least on I2C bus. APM2.5 baro is using SPI line so that cannot be removed but it is possible to have external baro connected. Software naturally needs to be changed and currently there are no support for external baros. I have been thinking this issue several times and might make soon one external baro for this type of purposes. 

Comment by Hai Tran on November 15, 2012 at 3:33am

Why doesn't APM2.5 have a plastic case like APM2.0?

Comment by Jani Hirvinen on November 15, 2012 at 4:06am

That I don't know, i think guys at 3DR are still working on it. Depends on the case, it still might need foam on top of baro.

Comment by Patch Thompson on November 15, 2012 at 4:33am

Controlling airflow around baro-based altimeters is crucial. Coming from a high powered rocketry background, I employ a controlled vessel, with calibrated holes, to establish a static ambient pressure environment for my avionics. In a plane or copter, it doesn't have to be so elaborate; a simple sealed plastic container with some strategically placed holes of specific dimension(as per the containers volume) should suffice. 

Essentially, this altimeter bay

Vern Knowles, an HPR guru, has documented using static ports for this purpose. Check out STATIC PORTS

Warning; rocketry is as addictive as DIYDrones........


Comment by Jean on November 15, 2012 at 5:12am

So instead of mounting an external barometric sensor, I can just put some small holes in the fuselage.  The holes should be small enough that they don't affect the aerodynamics too much.  Thanks so much for the info, Patch!

Comment by Jiro Hattori on November 15, 2012 at 5:25am

@Patch It is off topic. But so curious your rocketry work.


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