Due to high demand expect some shipping delays at this time, orders may not ship for 3-4 business days.
0

Expected output from BME688?
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Expected output from BME688?

by Technodad on Sun Jul 04, 2021 3:52 pm

I have a BME688 hooked up to a Funhouse via i2c. The temperature and humidity data seems OK, but calling bme680.gas returns 12946860 ohm, and hasn’t changed over the past 24 hrs. (Code is from https://learn.adafruit.com/adafruit-bme680-humidity-temperature-barometic-pressure-voc-gas/python-circuitpython#full-example-code-2997980-18, tweaked for the alternate i2c address.)

What’s a reasonable resistance value? Do I have a code problem, bad chip, something else?

Technodad
 
Posts: 9
Joined: Sat Jun 06, 2015 10:52 am

Re: Expected output from BME688?

by tannewt on Wed Jul 07, 2021 9:58 pm

What exact product do you have? It sounds like the library for the BME680 isn't fully compatible with the BME688.

tannewt
 
Posts: 2754
Joined: Thu Oct 06, 2016 8:48 pm

Re: Expected output from BME688?

by Technodad on Wed Jul 07, 2021 11:02 pm

I have the Adafruit BME688 STEMMA QT Product ID: 5046. It’s connected to the FunHouse by the 50mm STEMMA QT cable. The library was the BME680 library from the Adafruit site - I don’t believe there is a separate 688 library.

It’s possible that there is a difference in initialization or timing, but I’d expect more reports of problems.

I plan to do some testing from a Pi tomorrow, hopefully both CircuitPython and Node-RED.

Technodad
 
Posts: 9
Joined: Sat Jun 06, 2015 10:52 am

Re: Expected output from BME688?

by tannewt on Thu Jul 08, 2021 1:19 pm

Thanks for the details. I don't have one of these myself so let me find one of our support folks who do. Thanks for your patience!

tannewt
 
Posts: 2754
Joined: Thu Oct 06, 2016 8:48 pm

Re: Expected output from BME688?

by Technodad on Fri Jul 09, 2021 3:05 pm

I’ve put together a test program in CircuitPython in a Pi, and I’m seeing the same data coming from the sensor as on the code running on the FunHouse. The MBE688 is communicating with the program, and the temperature, pressure, and RH readings seem correct and responsive. The gas resistance however is stuck at 12946860 Ohms.

4C71181F-538F-47B0-9C2F-FA852FB89592.jpeg
4C71181F-538F-47B0-9C2F-FA852FB89592.jpeg (507.25 KiB) Viewed 195 times


I’ll give Node-Red a try, in case this is a library problem, but I’m increasingly coming to the conclusion I have a duff sensor.

Technodad
 
Posts: 9
Joined: Sat Jun 06, 2015 10:52 am

Re: Expected output from BME688?

by Technodad on Sat Jul 10, 2021 2:58 pm

I’ll give Node-Red a try, in case this is a library problem, but I’m increasingly coming to the conclusion I have a duff sensor.


Well it turns out that someone had already contributed a Node-Red node for the BME680https://flows.nodered.org/node/node-red-contrib-bme680-rpi, based on the Pimoroni BME680 library https://learn.pimoroni.com/tutorial/sandyj/getting-started-with-bme680-breakout. This saved me from having to use i2c directly, and made the test trivial. Unfortunately, the results were the same - the Gas sensor is stuck at 13MOhm, the same shown by the CircuitPython test.

As the sensor has now been tested in two different frameworks, I'm assuming it was DOA. On the plus side, I learned a lot!

Screen Shot 2021-07-10 at 2.03.49 PM.png
Screen Shot 2021-07-10 at 2.03.49 PM.png (182.36 KiB) Viewed 182 times

Technodad
 
Posts: 9
Joined: Sat Jun 06, 2015 10:52 am

Re: Expected output from BME688?

by adafruit_support_carter on Mon Jul 12, 2021 7:19 pm

This may be due to differences between the BME680 and BME688 specific to reading the gas resistance.

From the BME680 datasheet:
bme680_gas.jpg
bme680_gas.jpg (43.01 KiB) Viewed 152 times


From the BME688 datasheet:
bme688_gas.jpg
bme688_gas.jpg (47.07 KiB) Viewed 152 times


That would explain why the Node Red library did not work either. I'd suggest opening a new issue in the library repo:
https://github.com/adafruit/Adafruit_Ci ... 680/issues

adafruit_support_carter
 
Posts: 22293
Joined: Tue Nov 29, 2016 2:45 pm

Re: Expected output from BME688?

by Technodad on Thu Jul 15, 2021 9:00 am

Thanks, @adafruit_support_carter - glad to hear it might not be a dead sensor. Opened issue #42 on the library.

Technodad
 
Posts: 9
Joined: Sat Jun 06, 2015 10:52 am

Re: Expected output from BME688?

by adafruit_support_carter on Wed Dec 08, 2021 12:13 pm

Sorry this took so long. There was some discussion about best way to integrate the updates that sort of stalled. The fix is now merged and available in the 3.4.0 release:
https://github.com/adafruit/Adafruit_Ci ... /tag/3.4.0

adafruit_support_carter
 
Posts: 22293
Joined: Tue Nov 29, 2016 2:45 pm

Please be positive and constructive with your questions and comments.