Side Projects – Air Quality Sensor

As we have all been acutely aware the past few weeks, the air quality in the Bay Area has been abysmal at times due to the various wildfires. The smoke blanketing the area was the product of 10,000 buildings, and the nearly 100 people that perished. This was not just ordinary wood fire smoke. It was full of all kinds of nasty particulates, carcinogens, and burned over areas that previously contained radioactive waste. Not good. You could go to sites like to see what is going on regionally. But what about in your area specifically? Or even in your home? There are actually very few sensors in South County. One solution is which is a network of personally or corporate sponsored sensors. But they are again, expensive, around $250 or more with shipping.

There are certain benefits to these more expensive sensors. They typically have additional data like temperature, barometric pressure, and humidity. They also use dual sensors in a parity configuration to help ensure accuracy. But what if you don’t really need all that?

So why not build your own? For about $70 and a couple hours of your time, you can assemble the components and get a fairly good quality particulate sensor up and running for your home or office. You can get output that looks similar to this:

Current N6DZK air quality: PM1.0: 3ug/m3, PM2.5: 6ug/m3, PM10: 9ug/m3, PM2.5 AQI index 25 (good)

Electric Imp is a company that enables IOT (Internet of Things). They are based here in the Bay Area, and naturally were also impacted by the air quality crisis at the time. I have built projects with their products before. They have proven to be extremely reliable, with one project having been online for several years now. Over on their blog, their CEO and co-founder, Hugo Fiennes, published a post on how to build your own AQI sensor using their card, and a little development breakout board, and a sensor from Amazon.  So, why not? I ordered up the parts, and 3 days later assembled them together, ran the provided code, and had a working sensor telling me how dirty my home office air really is (turns out it was actually not that bad).

Follow the directions on the blog post. It is not much to look at, but it does get the job done for a fraction of the cost of commercial versions. And you can then alter the web page to look like anything you wish. It is cloud hosted, no local server to run or deal with. And Electric Imp has proven to be a robust, reliable, long term solution.

There are some intermediary steps that someone new to Electric Imp will have to complete prior to getting your sensor online. You will need to create an account, download the app to your phone that programs the Imp device to get on your home WiFi, and a few other minor steps. But Imp devices are remarkably easy to get up and running.



Category: DIY

Get on 40 meters SSB voice for $59
The BitX40 “you finish it” kit for $59

On tonight’s net, I mentioned that you can get on 40 meters for under $60, and without the need to be a virtuoso on the soldering iron or know tons about radios.  Say hello to the BitX40, an almost completely-finished 7 watt transceiver.  All you need to do is supply a box or case of some sort to put it in, a battery, and an antenna.  Everything else is already there for you.  To finish it, you solder on wires to a few controls, the battery (or 12 volt power supply), the antenna connector, and you’re ready to get on the air.

The BitX series of radios have an interesting back story.  A ham in India named Ashhar Farhan, VU2ESE, was concerned about how low the number of hams there were in his country, as well as other third-world countries.  After pondering this issue for a bit, he decided that one of the greatest problems a prospective ham faced was the high cost of even used ham equipment there.  He set out to make a 20 meter voice transceiver that used less than $20 in materials.  Thus was born the BitX20 about 10 years ago.  He cut costs in some very innovative ways.  For example, instead of the relatively-expensive ferrite toroids that are often used in radios, he substituted fiber or metal washers and wound his coils on them instead.  He decided to limit the power output to less than 10 watts so that a very common power MOSFET transistor could be used.  He also designed a novel main VFO tuning system made from a plastic drinking straw and a coil of wire.  I have one of these original (slightly improved) kits.

About 6 months ago, Ashar decided to try and help employ women in India to make a radio that might sell in higher quantities if he made it easier to build, but still supplied a quality product.  He created the BitX40, and founded a new small business to support it.  This is what I have in a my hands today, and I have to say that it is a very high-quality product, and he’s made it very easy to complete.

Gone is the drinking straw VFO, replaced by a very cool “Radiuino” board.  It is a very hackable Arduino that drives a 2-line LCD display and a DDS chip that outputs a highly-accurate, clean RF signal.  This one item alone increases the “fun factor” quite a bit, and helps contribute to a feeling that you are using a high-quality product that you yourself completed and mounted in your own custom housing.  Mount the display face and knobs to a plastic or metal ammo can and throw in a small battery pack, or put it in a cigar box (do they still have those?), or make your own custom wood enclosure.  It’s all up to you.

I suggest you give this cutie a try.  It’s not very intimidating, you’ll be very pleased with the results, and you’ll be helping some folks in India become more self-supporting.  You can find his website and ordering info here:



Ham Radio 360 Podcast features local hams

George, KJ6VU, has a great podcast and accompanying web page with some interesting gear and DIY projects going on. They are presently doing a group build of a 1-30 MHz antenna analyzer based on the Arduino platform. Have a look and/or listen at


I mentioned this on tonight’s tech net at 9 PM.  While you are perusing that website, have a look around at a few other very interesting things.  For instance, see George’s presentation from this year’s Dayton Hamvention, where he introduced the very handy portable end-fed antennas from his new company called PackTenna.


The presentation does a very good job of showing you how to wind some simple baluns (actually they are un-un’s) to get your 50 ohm feedline matched to the very high impedances of either a resonant, end-fed dipole, or a random-length end-fed antenna.  Or…you could buy one ready-made from PackTenna for $89.  If you go to and look around, be sure to read the QST magazine “test drive” of his antennas.  Highly recommended.

Amazon = Radio Shack + Frys + Halted + everyone else

This is probably old news for some of you, but if you miss having Radio Shack around, Amazon is the new Radio Shack, including all the other electronics parts stores rolled into one.

If you are a regular Amazon buyer, you’ve probably noticed that the Chinese “quick and dirty” module and parts suppliers that started out on eBay have all opened stores on Amazon now as well.  Being on Amazon generally means that they have to live up to a higher standard, if that kind of thing kept you from clicking the “Buy it Now!” button on eBay, but I’ve never gotten ripped off by any of them on eBay either.

Anyway, these guys offer just about anything imaginable for the Ham, DIY’er, or even an RF engineer like me.  I’m truly amazed at all the parts and pre-made modules you can buy from them.  If you have an Amazon Prime membership, which I highly recommend, you can buy just about anything and find it on your doorstep a day or two later, often without tax or shipping charges.

The prices are almost always way better than Radio Shack’s ever were.  Here’s just one example:  I needed to buy a 2.1 x 5.5 mm coaxial power plug–the type that you often see on the end of the “wall wart” power supplies.  Looking on Amazon, I had tons of choices, including whether or not I wanted some with wires already soldered on them and ready to go.  I finally chose these:

Coaxial power plugs with pigtails

So, for less than $.60 apiece, I got 10 plugs with wires already attached.  No tax charged, and free two-day shipping.  Can’t beat that!  Stock up for your next project!


Category: DIY

DIY Bluetooth Powered Speakers

Bluetooth BoomBox


There are dozens of videos on YouTube showing how to build your own Bluetooth speakers or boom boxes.  A number of them have ready-made Bluetooth radios and audio amps in common.  These Bluetooth and audio amp modules are interesting because they are quite cheap (most under $20–see this one on Amazon as an example), fully built and tested, and easy to interface to.  You could probably build one of these without even knowing how to solder!  It’s a simple matter to fit one of these small BT/amp boards into a box with speakers you’d mount yourself, or even retrofitted into an old plastic-fantastic boom box you have laying around, or maybe purchase for next-to-nothing at a Goodwill store.  All you really need is the housing and the pair of speakers.  Everything else can go!

For those of you that are old enough, remember the little transmitters you could buy or build that output a fairly unstable signal somewhere on the 88 to 108 MHz FM broadcast band?  They were often called FM or wireless mikes.  Plug one in, and tune in to it on of your FM radios you happened to have around the house.  They worked sort-of OK, but were never very good, and the 9V battery usually went dead in a few hours’ use.  In the Bay Area, you also had lots of trouble finding a fairly open radio channel to use.  The whole system was, as the British say, kind of fiddly.  It was more of a science experiment than anything else..

With Bluetooth, it’s so much easier, and the sound is just light-years ahead of the old analog FM stuff!  Most of us carry smart phones with Bluetooth built into them already, so it’s almost trivial to play the music or podcasts on your phone through your car stereo system or an inexpensive set of Bluetooth tabletop speakers.  Most of the cheaper BT speakers don’t have such great sound, though.  They tend to be small and tinny-sounding, but that’s not Bluetooth’s fault.

Anyway, here are several links to folks that have built their own Bluetooth speaker systems.  Maybe they’ll inspire you to roll your own:

DIY Bluetooth Speaker

Overnight Sensation Bluetooth Speakers

DIY Bluetooth Speaker: Super Easy

DIY V5.0 Boombox, Bluetooth

DIY How to Make the Best Bluetooth Speaker EVER!


Here’s an under-$20 BT dongle that plugs in to any 3.5 mm jack, giving you instant Bluetooth audio for a home stereo system or maybe even a car stereo.  This is sold by Parts Express (good company–lots of speakers and speaker kits as well), but there are many similar and cheaper units on Amazon as well:

Add Bluetooth to amplifiers, receivers, car stereos, computers, iPod docks


Emergency Power

2016-06-30 23.27.51The big one just hit. An accident just took out a utility pole. You forgot to pay your electric bill? All the things in your life that require go-go juice just became inert. But it doesn’t have to be that way. A few minutes on Amazon, and a couple trips to some of our favorite places to shop, and you can have plenty of electricity for lighting, communications, and charging your other devices. Read on to build one for yourself. Continue reading “Emergency Power”

Category: DIY