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AGP30, issues with CO2 VOC sensor

Started by Winfield Hill November 14, 2019
 Has anyone here used the Sensirion AGP30,
 a tiny I2C sensor for CO2 and VOC gases?
 It takes about 60mA to heat a hot plate,
 and it needs at least 15 seconds to start
 reading data.  But ours is experiencing
 shutoffs after 1.8 seconds when we run it
 from a Feather, but not if we run it from
 a Raspberry Pi.  Both controllers feed the
 PCB with 3.3 volts, where its regulated
 down to 1.8 volts with an TPS71718.  We
 communicate with the IC fine in both cases,
 and get the readings, but they're wrong if
 the hot-plate won't stay on for 15-seconds.


-- 
 Thanks,
    - Win
Winfield Hill wrote...
> > Has anyone here used the Sensirion AGP30, > a tiny I2C sensor for CO2 and VOC gases? > It takes about 60mA to heat a hot plate, > and it needs at least 15 seconds to start > reading data. But ours is experiencing > shutoffs after 1.8 seconds when we run it > from a Feather, but not if we run it from > a Raspberry Pi. Both controllers feed the > PCB with 3.3 volts, where its regulated > down to 1.8 volts with an TPS71718. We > communicate with the IC fine in both cases, > and get the readings, but they're wrong if > the hot-plate won't stay on for 15-seconds.
OK, nevermind, we figured it out, the sensor was OK. We've been flashing a bright LED every 5 seconds, as a heartbeat, visible in sunlight, and this was resetting the sensor. -- Thanks, - Win
Also, note that you need a baseline calibration in clean air, or it cannot detect “dirty” air

Cheers 

Klaus
Klaus Kragelund wrote...
> > Also, note that you need a baseline calibration in > clean air, or it cannot detect dirty air.
Yes, we're saving and bringing back the cal values. May I ask, how important is the humidity correction? It's a painful to do the absolute humidity conversion formula in an ARM M0 processor, without floating point. -- Thanks, - Win
On Friday, 15 November 2019 23:37:26 UTC+1, Winfield Hill  wrote:
> Klaus Kragelund wrote... > > > > Also, note that you need a baseline calibration in > > clean air, or it cannot detect dirty air. > > Yes, we're saving and bringing back the cal values. > May I ask, how important is the humidity correction? > It's a painful to do the absolute humidity conversion > formula in an ARM M0 processor, without floating point. >
I did not dig into the humidity effects on this sensor. Not much is written about the compensations, so I guess the effect is minor Cheers Klaus
On Fri, 15 Nov 2019 14:37:14 -0800, Winfield Hill wrote:

> It's a painful to do the absolute humidity conversion formula in an ARM > M0 processor, without floating point.
Just table-lookup it to death? You should have a lot of flash for detailed data, no?
Przemek Klosowski wrote...
> > On Fri, 15 Nov 2019 14:37:14 -0800, Winfield Hill wrote: > >> It's a painful to do the absolute humidity conversion >> formula in an ARM M0 processor, without floating point. > > Just table-lookup it to death? You should have a lot > of flash for detailed data, no?
Alan Stern, the Institute mathematician, who did all the programming for the beehive monitor, including the 14-sensor TH-stick, which includes the AGP30, tells me the floating-point libraries work just fine, but it's just slower. We do have the time, but maybe with all the huge masses of code he's written, he's running out of motivation to add more complication. -- Thanks, - Win
Winfield Hill <winfieldhill@yahoo.com> wrote in 
news:qstf07012rc@drn.newsguy.com:

> Przemek Klosowski wrote... >> >> On Fri, 15 Nov 2019 14:37:14 -0800, Winfield Hill wrote: >> >>> It's a painful to do the absolute humidity conversion >>> formula in an ARM M0 processor, without floating point. >> >> Just table-lookup it to death? You should have a lot >> of flash for detailed data, no? > > Alan Stern, the Institute mathematician, who did all > the programming for the beehive monitor, including > the 14-sensor TH-stick, which includes the AGP30, > tells me the floating-point libraries work just fine, > but it's just slower. We do have the time, but maybe > with all the huge masses of code he's written, he's > running out of motivation to add more complication. > >
Add more cores.
DecadentLinuxUserNumeroUno@decadence.org wrote...
> > Add more cores.
We're only using an ARM M0, and could chose an M4, etc., if we had placed the controller on the mobo. But the PCB didn't have room; we needed the extra space obtained by using an Adafruit Feather. -- Thanks, - Win
Winfield Hill <winfieldhill@yahoo.com> wrote in 
news:qstken01bnc@drn.newsguy.com:

> -- >
Use one of these to drive it... <https://www.solid-run.com/nxp-family/hummingboard/>