In astronomy, laser frequency combs are horribly expensive (~$0.5M), but fantastic for calibrating high precision spectrographs. It would be interesting to see if this method could be tuned for that application (namely, shifting to the visible), such to enable cheaper spectrographs.
Visible will always be expensive because it’s very niche and low volume. So the techniques here are only practical economically for the large volumes of light sources required for communications. This won’t extend to the visible unless there’s a similarly large market.
The cheapest way I’d think to generate a visible frequency comb would be to frequency double the IR comb laser using a nonlinear crystal like BBO.
Also here the accuracy is relative and not absolute which is fine for communications. The absolute accuracy of the comb may not good enough for spectroscopy in the visible.
Fog is condensed water droplets suspended in the air. Radiant heat , especially if it's optically focused, could remove them in the area where the PM sensor is looking.
I've been running multiple Sensirion SPS30 PM sensors for years, and I'm honestly amazed how well they've held up. Particularly with respect to, within their spec'd error, how new/unused SPS30s report similar values to my heavily used ones.
Curious if there are any maintenance requirements for the bosch sensor.
Do you actually do anything with the data you collect?
As someone who manages commercial building automation system installations, I have never understood the obsession that HN has with residential IAQ sensors. The number will go up if you cook, burn a candle, use a hairdryer, or if there’s wildfire smoke outside and you have a ducted HVAC installation with an outdoor air intake.
In a commercial BAS, IAQ sensors (CO/NO to be more specific) are used to turn on exhaust and make-up air fans to increase the air quality in a space, but in every single thread about IAQ monitoring on HN, nobody ever seems to use the sensor readings to automate their HVAC equipment to do anything. In fact, almost all commercial BAS systems have zero IAQ sensors (especially in offices), the vast majority of them are use for turning on exhaust fans and make-up air units in buildings where cars are driving inside, like a parking ramp or drive-in warehouse.
I guess my question is, why collect this information and do nothing with it? Maybe you actually do something with it, or you monitor local outdoor air quality as a hobby. I’m asking a more general audience than you specifically.
Lastly, ensuring your house is positively pressurized by paying a testing and balancing contractor to come over and adjust your HVAC system will do more to keep out particulate matter than measuring it ever will.
I use co2 measurements in my home to do just what you're describing here - automate control of a DIY fresh air intake (through a custom built filter box/fan enclosure w/ 5" merv 14 filter).
It's rather dumb at the moment, but when number gets too high, it kicks on for 1 hour and if it's back below threshold it shuts off. There's also a human presence detector that will "pause" it for 5 minutes since it's in my kitchen window.
It's built out of cardboard (laminated, with wheat paste) as a proof of concept/tinker with design and placement of things and also serves as a platform for the cats to nap in the window.
This, mainly, helps from bringing in all the outside humidity during the summer and the bitter cold during the winter. Otherwise, prior, I'd just keep an exhaust fan running all the time (eating the losses on air conditioning/heat) but we'd end up closing the window when it was super hot/cold and then the iaq would get terrible.
Lots and lots of people are automating their various systems due to monitoring these values. An application I've seen lots of is to just kick on the hvac systems fans when the aq drops below a particular threshold in one room or another.
> Lastly, ensuring your house is positively pressurized by paying a testing and balancing contractor to come over and adjust your HVAC system will do more to keep out particulate matter than measuring it ever will.
Sadly, it took me a while to figure out that having this window fan in my kitchen on "exhaust" rather than "intake" was creating a negative pressure environment and that was.. not optimal.
> I use co2 measurements in my home to do just what you're describing here - automate control of a DIY fresh air intake (through a custom built filter box/fan enclosure w/ 5" merv 14 filter).
That’s awesome! A cardboard POC that actually works is a cool project.
> Sadly, it took me a while to figure out that having this window fan in my kitchen on "exhaust" rather than "intake" was creating a negative pressure environment and that was.. not optimal.
Maintaining positive pressure is tricky, one thing that can help is monitoring outdoor air pressure and duct static pressure in the supply duct and controlling fans/dampers to maintain positive pressure by keeping indoor higher than outdoor.
I bought an Awair device in 2020 when my wife and I were working from home full time in the same room, out of curiosity as to whether our office area air was accumulating lots of CO2 during the workday (turns out this is not really an issue in drafty 120 year old houses).
In the time since I’ve found it helpful for: confirming my DIY air purifier was effective during wildfire smoke periods, having a reminder to open the windows generally when the air gets stale and particularly after cooking, learning that cracking a window for makeup air for the range hood makes it much more effective, getting better about trimming candle wicks and snuffing them instead of blowing them out, getting a sense of our actual temp and humidity comfort ranges and how they differ from thermostat settings, and realizing that induction really might be preferable to gas whenever we’re looking to buy a stove in the future.
I used to run https://www.open-seneca.org/. But, personally, it's nice to know the PM value whilst cooking, before going on a run, etc. Permits you to take informed decisions.
We've colocated many SPS30s with government reference stations, and the low cost sensor have always performed relatively well. But, more importantly for my use case, they are exceptionally inter-comparable.
Yes, and it is already happening in professional astronomy. For example, the "Antarctic Tianmu Plan" [0] have shown that you can successfully capture non-trailed images without using tracking mounts by using drift-scanning CCDs—basically letting the sky move across your sensor while the detector is read out at the same rate.
You can, but dark noise is a problem with this technique as your SNR per bucket ends up being low. The purpose of long exposures with tracking is to maximise your SNR.
Also, it helps significantly to be in Antarctica, where the relative movement is much slower than it is at lower latitudes — and to have multiple telescopes - and low noise CCDs, in a cold, dry environment.
what about computational methods? i have always wondered how stacking many short exposures without tracking compares to deconvolution of a single long exposure. it seems that there is software able to do this by taking into account both motion blur and the PSF of the imaging system:
The problem is that the noise can swamp the signal. Another example of this would be doing astrophotography during the day. The sun doesn't block anything, it just makes the sky glow with "noise". Theoretically it has exactly as much signal from space as it does at night, but because the sun adds so much noise it's completely lost.
> "because the sun adds so much noise it's completely lost."
Do you mean that it would be conceptually possible to image planets or even deep-sky objects during the day with incredibly efficient denoising software? (I am a noob in astronomy)
I would be, yes. As early as the 1950’s, several avionics companies made daylight-capable star trackers (for jam-resistant long-distance airplane navigation) using chopper techniques. Those trackers were mostly mechanical, except for electronics to demodulate the star signal from the single pixel sensor.
I suspect diffusion models can shine at denoising single shot deep sky images. Will be attempting when I find bandwidth. I do a lot of deep sky landscape photography (IG: @dheeranet) and I want to do them in one go instead of stacking ground (untracked) and sky (tracked) separately.
I really like the VS Code extension for sqliteview.app - [0]. It also offers an edit feature for a reasonable price, in my opinion. I'm curious if there are any competing editor alternatives.
