Thomas Käfer
I just stumbled upon your community while searching for gas sensors that are available to be bought by a "private customer" that only wants to have one or two pieces of each sensor, and not a hundred.
I have planned to use an "Arduino Leonardo" to measure the analog output signals of some gas sensors, send the readings via a (software defined) serial port to an openwrt running Linksys router and on (or via) that store the data somewhere for further processing.
Now the Arduino and the Linksys are not really a problem, the router I have lying around and I was able to aquire the Arduino for 15€ somewhere on the net.
My problem are the gas sensors. I ordered there: http://www.futurlec.com/Gas_Sensors.shtml since the prices seemed good, but that was a few months ago and in the meantime I canceled the order and got my money back since they where not able to deliver.
So if I found your community earlier maybe I could have "bought" one of your eggs through the kickstarter campaign. I also found somewhere here in the google group archive a post linking there: http://wickeddevice.com/index.php?main_page=product_info&cPath=28&products_id=108 but they say they show me a label "sold out". (And also 175$ is quite a lot money for me, especially if it only is able to read NO2, CO, temperature and humidity, and no smoke, no CO2, no VOCs)
So could you tell me good sources for gas sensors? It would be quite easy for me to get temperature and humidity sensors from a local reseller called "Conrad" here in Vienna, Austria, but I was not yet able to find a good source for gas sensors. Please help me out, thanks!
Gustavo Olivares
I've used Sparkfun and Adafruit to get small quantities of sensors ... have a look at this:
https://bitbucket.org/guolivar/pacman/wiki/Home
/El Gus
Victor Aprea
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kae...@gmail.com
2012/12/30 Victor Aprea <victor...@wickeddevice.com>:
> Do bear in mind that these sensors do require some maintenance to operate
> correctly, and that is the purpose for the Egg Shield, which is also
> avaiable from our store here. The shield comes all three sensors installed
> as well as the expansion headers that will provide access to add-on modules
> through the EggBus interface.
require maintenance"?
In my simple mind I imagined using the sensors by just wiring them up
and then measuring an analog voltage somewhere and depending on the
temperature and humidity readings from the same time these values can
then be interpreted as gas concentrations. Okey I've read that many
gas-sensors do need a "burn-in" phase of up to 48 hours, but from what
I understood this just means that they need to be connected to power
for that amount of time before the readings become accurate. Please
enlighten me.
Kind Regards,
Thomas K.
Victor Aprea
The sensors typically have an embedded heating element that should be controlled to within a certain range of output power in order for the surface temperature / chemistry to exhibit the resistance and gas selectivity described in the datasheets. The resistances of the sensors also tends to vary over quite a large range, so a "software-selectable" voltage divider on the sensing element helps deal with that. The Egg Shield has all that circuitry and software running on it to deal with these complexities. The hardware is described in detail here if you'd like to read further.
Cheers,
Vic
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Gustavo Olivares
Vic is right. The sensors usually require some kind of "babysitting" but the level of care depends on how "reliable" you want your data.
The AQE shield would be my recommendation to have something that will work and have a community behind.
Having said that, there are simpler (and less consistent) sensors out there (Parallax comes to mind) that are just "three wires" (gnd-vcc-sign/alrm). On the dust front, as far as I know, the Shinyei sensor is the simplest to use but the Sharp one is the smallest and cheapest. In the PACMAN I used those from Parallax and the Sharp dust sensor.
Keep posting your progress!
/El Gus
Thomas Käfer
Am Dienstag, 1. Januar 2013 03:01:48 UTC+1 schrieb Gustavo Olivares:
> Hi Thomas,
>
> Vic is right. The sensors usually require some kind of "babysitting" but the level of care depends on how "reliable" you want your data.
> The AQE shield would be my recommendation to have something that will work and have a community behind.
I understand, so the range of the resitance of the sensors is to big for a static wiring, but needs dynamic switching between different wirings.
The power source for the sensors heating I would have planned to use those "Current source" chips that deliver a constant current, and adjust the voltage as needed (within a range) Do you think that would work?
The problem that I have with the AQE-Shield, is that I would like to meassure a broader range of variables.
Gustavo Olivares
Vic would be better suited to answer in more detail but what I can say is that the shield can take more sensors communicating using the EggBus.
HOWEVER, some sensors (like the Shinyei dust sensor) require only 1 digital pin (plus power and ground) to work so it would not be too hard to connect it directly to your microcontroller if you're in a hurry and can't wait for the "Dust add-on" that's in the works.
Regards.