Monday, July 17, 2017

Replacing Dead Capacitors in Consumer Electronics


Be warned, this video starts a little slow, but once I get around to it, I go into very fine detail on how to spec out replacement capacitors to buy to replace failing ones in your equipment. Today's patient was a Netgear FS116 Ethernet switch.

Links to most of the needed equipment is listed in my Getting Started in Electronics post.

Thursday, July 6, 2017

Working a Professional Fireworks Show

Since this last "weekend" was the 4th of July, fireworks were happening... pretty much everywhere. This is the story of what I did with my Monday/Tuesday.

This wasn't the first time I've worked a professional show. I actually worked one last year, then promptly never got around to writing about it, so sorry about that, but the main question people ask there is how did I get into working professional fireworks shows once a year?

The answer is pretty simple: I answered the phone.
Me: "Hello?"
Laura (friend who happens to be a licensed pyro): "Kenneth. I know you like to do crazy stuff. My friend needs more hands to work a fireworks show. Would you be interested?"
Me: "Yes. yes. Matter of fact, yes I would. Dear god, yes. Yes."

Fast forward to this year, and she hadn't heard anything too terrible about my performance last year, so she invited me to work the City of Cupertino show with her this year, which is what I'm detailing here.
Monday (day before show), 10AM: The box truck arrives on site. This truck is carrying the racks of tubes for the shells, but not the actual fireworks.
 The first day is pretty much all just hard labor. Each of these plywood + 2x4 racks holds five 3" HDPE guns, and they all need to go from the box truck to the lawn.
A few packets of the show plan are floated around showing how many racks needed to be in each of the nine clusters (A-H) and how they should be grouped (set of three, pairs, etc).
 Once put in vaguely the right location, all the racks need to be nailed together so they don't fall over when the shells fire. I'll freely admit that I'm certainly not a pyrotechnics expert yet, but I was pretty quick to get on-board with the desire for the shells to go up first, and then explode.
While nailing them together, we also accounted for the expected wind direction with a bit of a general tilt to the right and the desire to give the shells some level of spread, so notice how we mounted them with some angle spread in each block.
After lots and lots of nailing, it was time to clean out the guns so they'd be ready to get loaded the next day. The last show who used these inevitably left all sorts of debris in the gun which we don't want below our fireworks, so it's a matter of checking each tube and cleaning it out.
After a hard five hours, we were pretty much ready for the fireworks the next morning and called it a day.

Show day, 10AM: The product arrives in another box truck. 860 pounds of glorious 1.3G explosives.

Due to the limited size of the field we were firing this show in, the show was limited to 3" shells, so they weren't going to be going particularly high, but we were making up for it in shear quantity. 950 loose shells, plus another 150 in "cakes," which are 25 shell clusters that just fire one after another, generally as the final crescendo to and during the finale.
We now had 11 hours to unpack all the fireworks, sort out which guns in which clusters each one was loaded in, and set them all up to get launched during the ~20 minute show. The cakes are real easy since they come pre-packaged, but we've got 950 loose shells that need to be laid out.

Before loading them in the guns, we place them on top of each gun for the inevitable shuffling of shells when we come up short of one kind and have a long string of the same kind or color in one of the blocks which would be visually boring. Swapping some of these for some of those in the next block, etc etc.

Notice how each shell is pre-wired for both electronic firing  via wire (which is what this show is using) and manual firing via the quick match fuse.
Quick-match is neat stuff. It's gun powder infused cord, which on its own burns relatively slowly (kind of like how everyone expects "fuses" to burn), but once you wrap it in a paper/tape wrapping to contain the burning gun powder, it becomes a propagating explosion, which runs down the quick-match at several hundred feet per second. When you want to manually set off a shell, route this stuff out the top of the gun, light the few inches of unwrapped fuse, DUCK, and it almost immediately goes up. Last year, I helped fire a show entirely manually, which literally meant that when the show started, the operator handed me a 20 minute road flare, and told me to start on one end of the row and while waving the flare around try to only launch one shell at a time.
 This show was instead an electric fired show, so we were using the electric squib wired to each shell.
This consists of fine gauge zipcord and what looks like a match head which has a resistive element in it to set it off when you pass enough current through it.
So now we've got ourselves a bit of a problem. We have 950 shells with electric squibs, and we need to wire all of them back to one place to be able to fire them all off. Thankfully they're all getting fired off in groups of two, or three, or more, so we can wire each group in series, but we're still talking about a LOT of wires.
For the larger 5-10 shell clusters, we don't bother wiring a squib to each shell, but actually splice them together using quick-match and one or two squibs at the end.
 So we need to wire all the shells. This is done off of an address sheet where each channel on each breakout box is listed with how many of which type of shell should be attached to it.
So we wire, and wire, and wire. Thankfully, others on the team were smart enough to bring pop-ups, so we were able to do this in shade, which was important, since this was the vast majority of the day.
And wiring and wiring and wiring... Seriously, I meant it when I said a LOT of wires. This is just one of the breakout boards. Each breakout has 45 channels, which are simple spring clips, and best I understand they all share 5 common ground returns through 50 pin Centronics connectors to the trunk lines back to the firing panel. Some of my Twitter followers rightfully so gave me a hard time for falling short of my usual wire management standard here, but it helps when you know that you're literally going to be blowing it up in a few hours and then frantically shoving it in trash cans.
After running the trunk lines back to the firing panel, we can do a continuity check on all the shells to make sure between the series wire splices, spring clips, breakout boxes, trunk lines, and the firing panel we don't have any opens.

Of course, we had several opens (see channel 3 in the photo above), so it was several iterations of checking the panel, noting down the open channels, turning off the panel, running out and finding the broken wires, fixing them, then clearing the field, then checking the panel, and figuring out which other wires we broke during the last round, etc. etc.
So this takes us up right to the show. To start the show, we light off one, then a second shell, to get everyone's attention and then show where the fireworks are going to be coming from. We then give everyone a minute or two to get themselves settled in and facing the right direction, before starting the electronics and running the show.

Yes. That is a photo of my hand, with a road flare. I was picked to set off the two starter shells, so I got to walk out into the middle of a lawn, filled with explosives wired to go off, light a road flare, and touch it to the first two fuses.

You know, when I put it like that... it really makes you ponder the life decisions that have gotten you to the place where you stand...
Then again, it was a pretty good view...

So then the show is over, and we need to go clean up the little mess we've made in the middle of some grounds keeper's pride and joy setting off 1100 explosives.
 Fire up the lights, and the hunt is on!
The hunt for the duds. We put a lot of effort into making sure that all the fireworks went off during the show, since that's pretty much the whole point of a fireworks show - it going up and being entertaining. Now it is time to find the shells which didn't entirely subscribe to this same objective for this evening and hadn't felt compelled to launch themselves into the air and the whole blowing up thing.

Poke a stick into each tube, check to see that it's empty, and pour out the shells that are still left and collected them in a pile. I know. Very technical.

Of course, getting another truck out here which is placarded and licensed to transport 1.3G explosives for just the six duds we had would be a bit of a waste of time, particularly when we've got 950 perfectly good launching tubes already set up, a fire marshal who's being a good sport, and 15 pyros who came to set off some fireworks.

Remember how each shell is both wired for electronic and manual firing? This is when the manual fuse comes in handy for setting off these six duds. This is also where I was handed a second flare and sent out to fire off another six shells manually. I mean, I don't mind, but I'm starting to suspect there's some not-in-their-20s self-preservation impulse for everyone else that kept resulting in me being the only volunteer for the manual shots...

Have you ever wondered why shows set off a few fireworks about a half hour after the show ends? This is why. They were just missed during the show and the operator really doesn't want to have to carry them home.
So it's now about 10:30PM, the fire marshal and our licensed operator have agreed that the explosives are all gone, and it's now a frantic rush back onto the field with hammers to dismantle the carefully nailed together racks and load them all back into the box truck. This takes us to just shy of 1AM, at which point it's some hearty hand shakes, hugs, and a wave farewell until next year.

Sunday, June 25, 2017

YouTube Channel IoT View Counter

I've wanted an Internet connected read-out for some time now, inspired by the awesome shadow box IoT projects Becky Stern has been doing (weather, YouTube subscribers). I'm certainly not to the same level of packaging as her yet, but I've got a functional display working with a Hazzah and an eBay seven segment display module.


Bill of Materials:

I soldered the Hazzah and display onto a piece of perf board I had laying around, which didn't work so well since the display was longer than the grid of the perf board.

I programmed the ESP8266 through the Arduino environment, which means you need to install the Arduino IDE, install the ESP8266 board module following their instructions, and install the YouTube API library through the library manager.

You'll also need to generate a Google API key for yourself, which you can do following the instructions on the YouTube API library's README.

The CHANNEL_ID macro is the random characters at the end of the URL for any channel of interest. For example, for my channel you'd want the part in bold:

The hardware is relatively simple: solder the provided headers onto the Hazzah, and connect the five needed lines from the Hazzah to the MAX7219 display:
  • Hazzah - MAX7219
  • V+ - Vcc
  • GND - GND
  • Pin 12 - CS
  • Pin 13 - DIN
  • Pin 14 - CLK

If you wire up the chip select, clock, and data lines differently, you should only need to change the macros at the top of the source code to correctly reflect your setup.

Of course, the possibilities here for packaging this display better are endless, as is using either the ESP8266 and/or these $2 displays to display any other information than YouTube channel view counts. The fact that these displays are chainable even makes it possible to make large multi-line displays with them.

Tuesday, April 18, 2017

Mastr 3 UHF Low Pass Filter Testing

Last year, I got a good deal ($50) on a pallet of Mastr 3 repeaters. They were all T band (490MHz) and more or less clapped out, but I figured it would be a good learning experience (and I got a nice tear-down video out of it).  Being way off the amateur band and wrought with problems, most of the electronics have been of little use to me and has been little more than a learning opportunity, but one piece I see myself being able to use elsewhere is the final low-pass filters from the power amplifiers (Part number 19D902856G9).
I've built low pass filters before, but wouldn't trust my own constructions to actually being put in use for where you need these filters the most on VHF/UHF, which is on repeater systems. Repeaters tend to be key-down for long periods of time, so power handling in the filters is important, and since they're remote if something goes wrong there's no one there to notice and getting to it to service it is generally inconvenient.  Since these low-pass filters off the Mastr 3s are already designed for high power (90W) continuous duty, they're perfect for my repeater applications (Usually 10W-25W) with the one exception that they're tuned for 470-512MHz, where all the repeaters I tend to build are in the 440-470MHz range.

That being said, 440-470 is lower than 470-512, so it's conceivable that the impedance in the pass-band might still be acceptable, and then the only downside is that I wouldn't enjoy quite as much filtering of the second harmonic than if the filter was really designed for 440-470MHz.
One thing I found interesting about the filter design was that it isn't symmetric! It's a 7th order LC filter, but the capacitors to ground only reduce in value on one side and not the other! My best guess as to why this is the case is that the engineers designing this filter knew that the output of the power amplifier wasn't perfectly 50ohms resistive, so they added a little reactance here to better match the amplifier.

To muddy the waters, the schematic and the physical unit I took apart don't agree on which port has the lower capacitance, and I wasn't careful enough when disassembling the amplifiers to say which port was actually connected where. I also enjoy that this model of the filter has black boxes instead of the inductance values filled in like on the other LPFs in the spec sheet; I'm not the only one fudging the documentation at times!

In any case, I just want to check the pass-band behavior of these in the lower 440-470MHz range, and see if these are something worth keeping or not. To the ungodly expensive vector network analyzer!
So on the top we've got the S21 plot going through the filter, so you can see the flat, low insertion loss, region on the left for the desired signals, and then the filter starts rolling off as you go higher in frequency, to the point where, on the right side of the plot, 900MHz is attenuated 45dB. The two markers 1 and 2 are at the two limits of my frequencies of interest, so you can see how the filter stays flat for much longer than I need before starting to roll off, so that 900MHz attenuation number could be better.

On the bottom, we see smith charts for the J1 and J2 ports (way zoomed in to see the detail around the center), so there's certainly an asymmetry to the filter, but both ports are decently close to 50 ohms so this isn't a game stopper. In an ideal world these filters would be a dot at the middle of the smith charts, which would be 50Ω + 0jΩ (50 ohms resistance plus zero ohms reactance), but they start wandering off into the wilderness as you go higher in frequency, which makes sense since the whole point of a low pass filter is that the insertion loss goes up with frequency, so the impedance usually does weird things (you can design flat impedance diplex filters if you care, but we really don't here)
So now lets zoom into the pass band we're interested in and check the SWR to sanity check that this filter is an acceptable match for my transmitters at my lower frequencies. Annnnd they are! This filter actually happens to bottom out its SWR curve right at 470MHz, so this filter is going to be great for my part 90 stuff, and still find for amateur stuff with an SWR of <1 .20="" 90="" a="" amateurs="" for="" gear="" have="" lower="" nbsp="" of="" p="" part="" radio="" standard="" than="" thumb:="" ule="">
Notice that this check was pretty valid, since the SWR starts sliding upwards at lower frequencies. I probably should have done a sweep further down in frequency to demonstrate how bad it can get once you wander outside the band the filter was designed for, but these measurements were being taken on borrowed time on the company VNA.

Great. In any case, now lets take it apart!
Ten screws reveal about what is expected, four inductors and three capacitors to ground.
Of course, at UHF the needed inductance is about one turn, so these are pretty minimalist inductors! The capacitors are a little odd; I haven't seen these sorts of clad mica capacitor before, but they're designed to handle the high RF current seen in a filter like this without needing to be huge for the power dissipation from using a normal termination instead of these heavy wrap-around metal bits. The rated working voltage for these capacitors is just 100V, which was a bit surprising to me, but makes sense once you consider that this is a 50Ω 90W system.
My favorite part of the die-cast shield is the little cutouts in the walls leaving a gap where the strip line passes underneath the dividers between stages. I don't know if those are designed for a critical dimension or just "tiny gaps."

In any case, I've now got a pile of these great LPFs for various repeater projects. They're usable as-is, but I can always go in there and tweak inductor/capacitor values if I want to use the chassis for something else (or actually tweak them down to my frequencies of interest).

Tuesday, March 7, 2017

Podcast Interviews on APRS

When it comes to amateur radio, APRS is pretty near and dear to my heart. I did my masters thesis on it, and I'm now the maintainer of Aprx, which is one of the most popular digipeater software packages.

I recently started talking to Cale, K4CDN, and have recorded a pair of podcast episodes for HamRadio360 on APRS. Enjoy:

  1. All About APRS with W6KWF
  2. APRS Follow-up (Listener Q&A)

Tuesday, January 17, 2017

APRS Symbol Look Up Table

Click to Enlarge
In APRS, symbols on the map are encoded as two ASCII characters. The first character selects the table (primary or secondary) and the second character selects the symbol from that table. (The table selector can also be used as a alphanumberic overlay on top of the secondary table)

The symbol list is available online here, but I've always wanted an easy-to-use graphic with the symbol codes and the icons right next to each other. I finally broke down this week and created the image you see above based on Hessu's great APRS vector symbol set. Click on the table to see it in full resolution.

To use this table, simply find the icon you want to use, read off the symbol code above it, and use "/[symbol code]" if it's in the middle square and "\[symbol code]" if it's in the bottom square.

Sunday, January 1, 2017

2016 Retrospective

It's the end of the year, so I figured I'd do a general life recap and wax on what I'm looking at in 2017.

First and foremost, I changed jobs this year. I'm now an electrical engineer at Lam Research in the etch engineering group, where I'm working on their wafer plasma etchers used in semiconductor fabrication. This is particularly fun because I got this job through one of my Cal Poly Amateur Radio Club cohorts, so I get to see him nearly every day (thanks Sean!). It's an interesting group to work in since wafer processing spans a wide breath of fields including power systems, vacuum tech, RF power, embedded controls, etc. Most of my workload is related to my experience in RF systems, so designing RF filters, but the Lam Etch Engineering group is organized in such a way that I enjoy a high level of diversity in the problems I get assigned to, so I'm not concerned about ever getting pigeon-holed into just working on RF.

My group at Lam has been growing very quickly this year. Even just since I started we've hired three more EEs and looking for a few more. If you're in the bay area and looking for a job feel free to shoot me an email if you're interested.

My personal hobbies have continued to be involved and time consuming. My previous new year's resolution was to get back into public speaking and give four talks to radio clubs. I only ended up developing two new talks this year, but there was enough interest in them to take them on tour and give the same talks several times so I think it mostly counts as a success:
I've been having fun building and deploying radio repeaters. On the bench side, I've been putting together a collection of videos on repeater building [1][2][3][4]. Online information on repeaters is tough to come by, and I don't feel like I've even made a dent yet, so plenty more repeater videos are yet to come. On the repeater deployment side, I got to spin up several of my personal repeaters at events like the Wildflower Triathlon under my commercial radio license and at the Bay Area Maker Faire on the amateur repeater test pair.

In addition to working communications for the Wildflower Triathlon for TriCalifornia, I got talked into volunteering for several other of TriCal's events. A dedicated communications team isn't needed for their other events, so I instead got to work on the course team placing cones and traffic control around the race courses for the Pacific Grove Triathlon, the SF Triathlon at Alcatraz, and the Giant Race. Getting to drop traffic cones off the back of a moving box truck is a kick.

Sadly, TriCalifornia recently announced that they're not hosting any of their own events in 2017, so my event support in 2017 is going to need to be more diverse.

I've been having fun climbing towers for the Salinas Valley Repeater Group this year. They're a good group of guys with an impressive repeater network set up covering the bay area down to Fresno. I love tower climbing since it's a good day of exercise on top of a great excuse to get tours of radio sites.

In the category of "crazy adventures I never got around to writing about," one of my friends this year called me up at the last minute in the end of June:
"Hey Kenneth, I know you like to go on crazy adventures. You want to help one of my friends put on a commercial fireworks in Ft Bragg?"
Yes. Yes I do.

It ended up being a full day experience of get up at 5am, drive up to Ft Bragg, spend the afternoon unloading 650lb of fireworks and the corresponding gun racks out of a box truck, and then firing the show before crashing in a motel. The fun part about these "hand-fired" shows is that we don't use a mile and a half of electronic matches to light off the shells but I get handed a 20 min road flare at the beginning of the show and get to run around using the road flare to light off the fireworks.


So now for the question on what I want to try and do in 2017. My tradition of trying to pick up a new hobby every year started getting more difficult recently mainly because my hobbies (repeaters, beer brewing, tower climbing, etc) all tend to be so equipment intensive that my apartment is starting to get ridiculous with all my stuff.

I think I was on to something good with the 2016 "public speaking" objective, so I think I'm going to go on a similar vein this year and try and get four magazine articles out the door. I've been complaining about how disappointing the amateur radio magazines have been long enough that I just need to put up and start delivering the content I want to read. The ARRL also pays pretty decent money for accepted content too, so that's a nice perk that this year's hobby might actually be cash positive for once. We'll see at the end of the year as to how I do.

Here's to another year, and I hope all of your objectives and achievements find you in good health as well!