Questions and discussions about the hardware aspects of the TD RF modules, boards and accessories.
disk91
 
Posts: 58
Joined: Thu May 07, 2015 4:30 pm

GPS impact on accelerometer

by disk91 Sun Jul 05, 2015 7:43 pm

Hello,

During my test I discovred that Accelerometer feedback is different when GPS is activ of not. Do you have an explanation or work-around to avoid this ?

Sincerely,
Paul
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lcheminade
 
Posts: 145
Joined: Mon May 11, 2015 7:47 am

Re: GPS impact on accelerometer

by lcheminade Mon Jul 06, 2015 7:16 am

Hi Paul,

Both are sharing the same SPI bus which means they can't receive data at the same time. The GPS is flowing quite a lot of data so if you also need a lot from the accelerometer it's going to be an issue.

By the way the radio chip is also sharing the SPI bus so using Sigfox transmission will block both GPS and accelerometer during the transmission time. Same apply for LAN application.

Anyway could you please further detail your application and what difference you see?

Thanks.

Loïc
disk91
 
Posts: 58
Joined: Thu May 07, 2015 4:30 pm

Re: GPS impact on accelerometer

by disk91 Mon Jul 06, 2015 8:56 pm

Hello, I did not experience bus conflict even if it can be the reason, in fact actually I'm only using accelero at 10Hz and once every 30 seconds so I do not need a large acess to the bus.
What I noticed is where the device is not moving with GPS off, the values returned by Accelero are about +/- 30 but when the GPS is on, the values are moving to +/- 100 so this was impacting my movement detection procedure and sounds not a fully normal behaviour.
I have a workaround for this in my code but as it sounds not normal i'm reporting it.

Paul
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lcheminade
 
Posts: 145
Joined: Mon May 11, 2015 7:47 am

Re: GPS impact on accelerometer

by lcheminade Tue Jul 07, 2015 8:50 am

Ok I understand what you mean. Sounds like GPS is increasing the noise level in the accelerometer. Never noticed that so thank you for reporting!

I'll investigate and let you know about it.

By the way note that the accelerometer can be sensitive to temperature as well.
disk91
 
Posts: 58
Joined: Thu May 07, 2015 4:30 pm

Re: GPS impact on accelerometer

by disk91 Tue Jul 07, 2015 8:24 pm

Thank you for investigation and also for temp advice I'll investigate that to to prevent unexpected behavior.
Paul
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lcheminade
 
Posts: 145
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Re: GPS impact on accelerometer

by lcheminade Tue Aug 04, 2015 8:08 am

Hi Paul,

I just gave it a try but didn't see much difference with or without GPS. Could you please give me more details about what you're doing?

Thanks.
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