I see what you mean. I didn’t realize about the conversion method. They are closer now, but like you said, still a bit off.
Thank you.
@posburn is it possible to add the ability to select which channel it uses (A vs B)? My sensor has a borked channel B and the reading is like 2k. On PurpleAir map, it shows the value from A it seems like (normal reading), but in Tidbyt it is displaying the 2k value.
Hi @skurvy_pirate - the Tidbyt app averages the A and B sensors as PurpleAir recommends. I bet they check both values first to make sure they are valid before using them. I should add that to the Tidbyt app. I could check both and if one is not valid, I don’t use that one and use the other. I’ll see about adding that. Thanks for letting me know.
Also, it’s possible one of your sensors needs to be cleaned - have you read this before?
@skurvy_pirate @whoster - I’m working on an update to the PurpleAir app that fixes a few bugs I’ve found when calculating the AQI and adds a config option to select the sensor to use in the calculation. Thanks for that suggestion @skurvy_pirate!
@whoster I’ve also discovered that my code does not handle the case where a PurpleAir device only has one sensor. It always assumes an A and a B sensor are present, which can greatly affect the AQI I calculate in this case. I’m addressing that as well.
Finally, I’m looking into using the confidence score that the API returns for the device. On the PurpleAir map you can see sensors that have a low confidence value easily as they are shown with transparency. The lower the confidence, the less opaque the circle is. I thought that might help @skurvy_pirate as you could check your sensor on the map and see if it is more transparent or not.
If anyone has any feature requests or suggestions now is a good time to let me know. 
1 Like
That’s great information, posburn! Thank you so much for the update! Let us know when you have it in place and I’ll be glad to test it for you and tell you how accurate it is for the sensors I’m using.
Thanks @posburn! Yeah it appears PurpleAir map is discarding the bad value. I guess you could do something similar but might be interesting/tricky to determine when you are getting bad data from one of the sensors as you might not know if the lower or higher value is the bad value. PurpleAir might be looking at nearby sensors to help make this decision to decide which sensor is bad? My sensor has a confidence of 0 lol (rightfully so, one channel is completely off the charts). I tried blowing it out with pressurized air already but plan to open it up to try and blow it out a little better when I get a chance. Otherwise will be looking to buy a new sensor to replace.
Makes sense. I read on the PurpleAir forums somewhere they have a sensor replacement you can buy. I think it was $49 and replaces both A and B sensors and you can do it yourself. Much cheaper than buying a new PurpleAir device.
The updates for the PurpleAir app are live now. The app now handles devices with low confidence PM sensors and devices with only 1 sensor. You can also choose which PM sensor to use in the configuration options. The default is the average of the A & B sensors if both are working correctly.
A different EPA AQI formula is used and I discovered I was not using the PM values with a correction factor applied. Now the app uses the corrected values.
So, with all of that, I hope you’ll find that the AQI value the Tidbyt app shows is closer to what you might find on the PurpleAir map.
Let me know if you have any other suggestions or feedback. Thanks for your help!
1 Like
It’s possible the update to the PurpleAir app isn’t live yet. Let me know when you see the new Particle Sensor option.
@posburn I use the PurpleAir, and I shared your announcement with a PurpleAir users group on Facebook. Unfortunately, because I don’t have a Tidbyt (yet), I can’t see what your app looks like, which also means I can’t share images with anyone. The Tidbyt app seems to require pairing with a device before it will show any apps for the device. Can you share some photos of your Tidbyt showing PurpleAir data and whatnot? If the app is noteworthy, maybe that also?
Thanks for your post @ejm554 and for sharing on the PurpleAir users group! It turns out Tidbyt has an Apps page you can view in your browser (no Tidbyt required). Click ‘Live’ at the top and then search for PurpleAir and you’ll see a small animated preview of the app. There is a larger, static preview here.
You’re welcome. Thanks for building it. Now I just need to find a way to acquire one of these Tidbyts!
For those who haven’t seen the preview, I’m including a copy in this message.
is purple drawing from the same data as the EPA stations? https://aqs.epa.gov/aqsweb/documents/data_api.html
It’s not. The PurpleAir app pulls data from the PurpleAir APIs. You can take a look at purpleair.com for more info.
seems the PurpleAir app isn’t working correctly. it now wants both the API Key and the Sensor ID. How do I get the API key from the map?
1 Like
I have the same question. the PurpleAir app stopped working yesterday. I would love to see a fix.
Thank you.
@robbo980 @whoster - purpleair charges for API calls (they give you a bunch for free) - but the original dev was getting charged for the folks that were using the app. So the decision was made to require users to get their own API key for it. go here: PurpleAir Develop create an account. Create an organization, create a project & create a READ key. Then you’ll have a key to enter. The PurpleAir folks don’t have the greatest doc on how to do it, but here’s a link to the “getting started” page they have, Making API Calls with the PurpleAir API - API - PurpleAir Community
Well, hrm.
Currently all i see is a message “Specify a sensor and API key.” OK…
- got a key from PurpleAir, (big old UUID which is a secret)
- located the sensor ID from PurpleAir’s map (178415)
- reinstalled the Tidbyt app
- did a factory reset, just for fun.
(I appreciate the great app. Just looking for a sanity check!)
Chris
make sure you’ve allocated points to your project from your organization. it’s not apparent that you have to do this (purpleair has stated they are working on this to make it easier). But go into your project & do an edit. if your current project points is 0 - you can’t make any calls.
it should look something like this.
4 Likes