openXsensor V8.0 16bit ADC and analog Airspeedsensor

Development & General Chat for the superb openxvario project.

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Carbo
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openXsensor V8.0 16bit ADC and analog Airspeedsensor

Post by Carbo » Tue Mar 07, 2017 12:39 pm

Mstrens extended the possibilities of oXs: oXs supports now ADS115, which supports 4 16bit ADC (or two differntial ADC). Also a (cheaper) analog airspeed sensor MPXV7002DP can be connected.

ADS1115 datasheet
Sensor kit

oXs_config_description.h includes the needed informations. Yes, the sandwich includes also an arduino pro mini.
Boden.png
Top.png
The noise is acceptable:
7002Noise.png
//The sensor seems to add an offset to the measurement.// <-- Edit: wrong, there is no offset! It shows exactly, what we should see:
pre_aspd.png
pre_aspd.png (6.13 KiB) Viewed 721 times
The log shows the cooldown of a closed 35 cm silicone tube attached to the speed sensor. The tube was prior heated with my hand. The polarity is wrong, because i connected the sensor to ADS1115 wrong (swapped A0 and A1). These things happen, if one does not take care of the instructions in oXs_config_description.h ;)
7002Zerocrossing.png
Edit: The sensor shows indeed very good results.

Carbo
Posts: 249
Joined: Fri Aug 02, 2013 6:55 pm
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Re: openXsensor V8.0 16bit ADC and analog Airspeedsensor

Post by Carbo » Wed Mar 08, 2017 7:01 pm

MS5611 (filtered) (red) vs. MPXV7002DP analog out over ADS1115 (blue). The voltage scale is x0.1. Looks promising.
7002vs5611.png

Carbo
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Joined: Fri Aug 02, 2013 6:55 pm
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Re: openXsensor V8.0 16bit ADC and analog Airspeedsensor

Post by Carbo » Sat Mar 18, 2017 7:31 pm

Mstrens added the code for dte vario and it is benchtested. It requires a RC filter of 100nF and 100kΩ connected to the analog out of the airspeed sensor to achieve a good 'sounding' dte variotone. The reaction time for airspeed change is still approximately instant.
Filter.jpg
Benchtests were made in a pressure chamber, with identical pressure for baro and airspeed. Static pressure for the airspeed sensor was taken from outside the chamber. Rising and lowering the pressure had nearly no influence on the dte vario tone. Rising pressure means more airspeed and less altitude and vice versa and this stands for the exchange between potential energy and kinetic energy. Flying tests will be done as soon as the weather permits. I like to search thermals with dte vario and circle with baro vario. The switching between dte and baro and the reset of airspeed (in case of an offset after boot) can be done with a PPM signal connected to PIN3.

PPM 10 --> 40 baro vario and control of vario sensitivity from 20-200
PPM -60 --> -90 dte vario and control of energy compensation from 80-140%
PPM 100 --> airspeed reset
PPM.png
PPM.png (6.48 KiB) Viewed 641 times
L1 is SH AND rudder -100 to prevent airspeed reset in flight.

Values are valid for this
oXs_config.zip
(4.53 KiB) Downloaded 16 times

Carbo
Posts: 249
Joined: Fri Aug 02, 2013 6:55 pm
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Re: openXsensor V8.0 16bit ADC and analog Airspeedsensor

Post by Carbo » Thu Mar 23, 2017 2:37 pm

Flight peformance is also OK. Dte vario is still a little noisier than the baro vario and needs more RC filtering, but it is already useable.

This is an example where i switched from dte (plane flying phugoids unintentionally-you do not hear them because of energy compensation) to baro vario, where i immediately and unconsciously calmed the plane down.
Comp3red.png

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