Adoption of XGZP6897D Differential Pressure Sensor

[jasc76]

Datasheet

XGZP6897D-Pressure-Sensor-V2.7.pdf

In Test is the 3.3V 500Pa Variant. Currently the sensor is recognized, but no measurements are displayed when using FV. In parallel a GY-63 is connected so I²c should be terminated without using pullups

Baro sensor is detected using MS5611
Sensitivity min = 100 (at 100) , max = 300 (at 1000)
Hysteresis = 5
Airspeed sensor is detected using XGZP....

[jasc76]

Just downloaded the 2.12.4 Version and will try to get some debug data

If you like I can send you one of these sensors (if you are in the EU... US takes ages) . I got 2 :-)

[mstrens]

Perhaps we can find the issue with the debug messages.
In a second stage, if I do not find the issue, then getting a sensor could help.
I am in EU (Belgium).

[jasc76]

looks good, values are definitely changing when blowing over it

rawPres=66695
rawPres=172799
rawPres=33783
rawPres=3823
rawPres=16777142
rawPres=115830
rawPres=205088
rawPres=320911
rawPres=486299
rawPres=16737849
rawPres=16747550
rawPres=16740163
rawPres=16736876
rawPres=783477
rawPres=16728544
rawPres=531232
rawPres=1093841
rawPres=1124545
rawPres=1056067
rawPres=649749
rawPres=16735820
rawPres=16743526
rawPres=16740288

[mstrens]

In the version you tested I made 2 changes:

• one to add a debug message
• one to fix a minor bug. It is perhaps this fix that solved the issue.

[mstrens]

I made a new version 2.12.5 in order to manage negative pressure (the sensor is differential and so some values can be negative.
Without this correction, negative values were processed as very big values and could generate wrong results.
I hope it help to get more realistic airspeed.

[jasc76]

you're a wizard :-)
depending, which port gets the air pressure the value is pos or neg now. I guess ignoring pos/neg makes the most sense since its irrelevant for the application

rawPres=-30229
rawPres=-28695
rawPres=-1945446
rawPres=-40881
rawPres=-51391
rawPres=-27898
rawPres=-88071
rawPres=-73877
rawPres=-324429
rawPres=-889948
rawPres=898187
rawPres=773595
rawPres=-70024
rawPres=79785
rawPres=1257551
rawPres=700077
rawPres=-64377
rawPres=-61067
rawPres=1076767
rawPres=-61751
rawPres=-35367
rawPres=-30116
rawPres=-29381

[jasc76]

hmm. at the same time there seems to be a lot of noise

rawPres=1733
rawPres=3086
rawPres=-218
rawPres=1984
rawPres=4579
rawPres=1337
rawPres=175
rawPres=-1214
rawPres=-2869
rawPres=-1598
rawPres=-1104
rawPres=1779
rawPres=1744
rawPres=862
rawPres=335
rawPres=-1252
rawPres=-547
rawPres=103
rawPres=246
rawPres=1398
rawPres=1641
rawPres=-8
rawPres=-348

[mstrens]

Yes but this is perhaps not so abnormal.
A raw value like 2000 means in fact a pressure of 0.25 Pa which is equivalent to a speed of 2km/h

Best is to check the airspeed calculated by oXs and see if it is realistic.

Do not expect an realistic value when speed is less than about 15 km/h because this result of very low difference of pressure.
When speed get higher, then accuracy/noise of airspeed becomes better.

[mstrens]

FYI tTaking into account the negative values is not bad:

• when program starts, oXs takes the average of several measurements to calculate an offset that is applied to the following measurements
• when oXs calculate the airspeed, if the pressure is negative, oXs converts it to a positive value. This allows to connect the pitot tube in both directions on the sensor.

[jasc76]

ok cool

Currently this is all a crude test setup botched together with some wires. I now ordered stuff to actually mount it to my glider. I would assume I put it in the plane, hook up SBUS and tweak the compensation adjustment channel until I get a consistent result. Is this correct !?

Which oXs version should I use now? The master or still test?

[mstrens]

Use always test branch. I put all new functions there. Still take care that there can be some not yet known bugs.

Some users tested the airspeed while running with a car. One man drives the car, another hold the pitot tube outside. The value is read on the handset.

[jasc76]

Do I have to change the k value in the code or is the calibration done solely done with the compensation channel ?

[mstrens]

You have to change manually in config.h the value for XGZP_K_FACTOR
It depends on the max pressure of the model you selected.
Here the text in config.h
#define XGZP_K_FACTOR 8192.0 ; // See datasheet : K depends on the sensor model (related to the max pos pressure being measured)
// 8192.0 is the value when max sensor pressure is 1000Pa (1kPa) like XGZP6897D001KPDPN

[mstrens]

The compensation is a parameter used only for the compensated aispeed. it does not matter to calculate the airspeed.

[jasc76]

I dont really care for airspeed, I'm just interested in the vario compensation. So my thought was not to bother with the k value. Also in the datasheet, all models below 1kPa have the same k value.

[jasc76]

hmm
I wanted to do the calibration, I used the current test branch 2.13.1 and I get changing raw values. However with FV airspeed is always 0. I did not hook up a receiver and just used usb

rawPres=-683676 rawPres=-734410 rawPres=-800049 rawPres=-25184 rawPres=-217883 rawPres=-1596020 rawPres=-1711642 rawPres=-1651593 rawPres=-28809 rawPres=-33805 rawPres=-1309954 rawPres=-635123 rawPres=-1202301 rawPres=-690018 rawPres=-769427 rawPres=-567340 rawPres=-958961 rawPres=-1552390 rawPres=-1172935 rawPres=-1505920 rawPres=-1097496 rawPres=-78826 rawPres=-33733 rawPres=-2576 rawPres=-6549 rawPres=-4949 rawPres=-8274 rawPres=-7904 rawPres=-4487 rawPres=-22924 rawPres=-32619 rawPres=-3220531 rawPres=-2690748 rawPres=-3060192 rawPres=-3926 rawPres=-4940 rawPres=-1513 rawPres=-2688 rawPres=-6399 rawPres=-7482 rawPres=-5073 rawPres=-6046 rawPres=-8062 rawPres=-5920

`Version = 2.13.1
Function GPIO Change entering XXX=yyy (yyy=255 to disable)
Primary channels input = 5 (PRI = 5, 9, 21, 25)
Secondary channels input = 255 (SEC = 1, 13, 17, 29)
Telemetry . . . . . . . . = 255 (TLM = 0, 1, 2, ..., 29)
GPS Rx . . . . . . . . . = 255 (GPS_RX = 0, 1, 2, ..., 29)
GPS Tx . . . . . . . . . = 255 (GPS_TX = 0, 1, 2, ..., 29)
Sbus OUT . . . . . . . . = 255 (SBUS_OUT= 0, 1, 2, ..., 29)
RPM . . . . . . . . . . = 255 (RPM = 0, 1, 2, ..., 29)
SDA (I2C sensors) . . . . = 10 (SDA = 2, 6, 10, 14, 18, 22, 26)
SCL (I2C sensors) . . . . = 11 (SCL = 3, 7, 11, 15, 19, 23, 27)
PWM Channels 1, 2, 3 ,4 = 255 255 255 255 (C1 / C16= 0, 1, 2, ..., 15)
PWM Channels 5, 6, 7 ,8 = 255 255 255 255
PWM Channels 9,10,11,12 = 255 255 255 255
PWM Channels 13,14,15,16 = 255 255 255 255
Voltage 1, 2, 3, 4 = 255 255 255 255 (V1 / V4 = 26, 27, 28, 29)
RGB led . . . . . . . . . = 16 (RGB = 0, 1, 2, ..., 29)
Logger . . . . . . . . . = 255 (LOG = 0, 1, 2, ..., 29)
ESC . . . . . . . . . . . = 255 (ESC_PIN= 0, 1, 2, ..., 29)
Locator CS . . . . . . . = 255 (SPI_CS = 0, 1, 2, ..., 29)
SCK . . . . . . . = 255 (SPI_SCK= 10, 14, 26)
MOSI . . . . . . = 255 (SPI_MOSI=11, 15, 27)
MISO . . . . . . = 255 (SPI_MISO=8, 12, 24, 28)
Output level High . . . . = 255 (HIGH = 0, 1, 2, ..., 29)
Output level Low . . . . = 255 (LOW = 0, 1, 2, ..., 29)

Esc type is not defined

Protocol is Sport (Frsky)
CRSF baudrate = 420000
Logger baudrate = 115200
PWM is generated at = 50 Hz
Voltage parameters:
Scales : 1.000000 , 1.000000 , 1.000000 , 1.000000
Offsets: 0.000000 , 0.000000 , 0.000000 , 0.000000
No temperature sensors are connected on V3 and V4
RPM multiplier = 1.000000
Baro sensor is detected using MS5611 at I2c adress 77
Sensitivity min = 100 (at 100) , max = 300 (at 1000)
Hysteresis = 5
Airspeed sensor is detected using XGZP....
No Vspeed compensation channel defined; oXs uses default settings
First analog to digital sensor is not detected
Second analog to digital sensor is not detected
Foreseen GPS type is Ublox (configured by oXs) :GPS is not (yet) detected
Led color is normal (not inverted)`

[mstrens]

What do you mean with "calibration"?

At power on oXs makes several (32) measurements and uses the average as offset.
So this is an automatic calibration.

[jasc76]

ok
I get now also Airspeed.
But I guess you need to show the absolute value, because I get neg values :-)

processing cmd

Cmd to execute: FV

Vspeed = 3 cm/s
Baro Rel altitude = 24 cm
Airspeed = -1235 cm/s
Compensated Vspeed = -1529 cm/s
pwmTop= 20000
rawPres=-733749 sumPa=-86.113831 count=1
rawPres=-1275134 sumPa=-152.200867 count=1
frawPres=-22982 sumPa=0.649719 count=1
v
processing cmd

Cmd to execute: FV

Vspeed = 1 cm/s
Baro Rel altitude = 30 cm
Airspeed = 28 cm/s
Compensated Vspeed = 187 cm/s
pwmTop= 20000
rawPres=-34739 sumPa=-0.785461 count=1
rawPres=-304483 sumPa=-33.713196 count=1
rawPres=-2581819 sumPa=-311.708313 count=1
fvrawPres=-3587696 sumPa=-434.496033 count=1

processing cmd

Cmd to execute: FV

Vspeed = 1 cm/s
Baro Rel altitude = 32 cm
Airspeed = -2541 cm/s
Compensated Vspeed = -1600 cm/s
pwmTop= 20000
rawPres=-3573326 sumPa=-432.741882 count=1
rawPres=-27387 sumPa=0.112000 count=1
rawPres=-27745 sumPa=0.068298 count=1
rawPres=-18979 sumPa=1.138367 count=1
rawPres=-11486 sumPa=2.053040 count=1
rawPres=-12270 sumPa=1.957336 count=1
rawPres=-11181 sumPa=2.090271 count=1

[mstrens]

I use negative values because they can help during the calibration process (to calculate offset)
Do you test with a pitot tube or just applying a pressure on one of the entry of the sensor?
With a pitot tube, you should try to invert the 2 tubes (this should invert the sign.