Author: Jack

TEAPOT: The electronically actuated pneumatically operated transmitter

the electronically actuated pneumatically operated transmitterA couple days ago, before the NAQP-CW, Pete K6BFA mentioned that before the start of the contest, some Boy Scouts would come over to the club station to talk about learning morse code. This wasn’t about working towards a radio or electronics merit badge: they wanted to learn the code for team competitions in which they are required to send messages to each other in the field using whistles.

Before they came over, we thought about how people learn code, and figured that for their purposes, they could use traditional tools for learning morse code (like the LCWO site, MorseResource, and various programs for PC or smart phone), but they’d be best served by practicing with actual whistles.

This got the gears turning, and more out of curiosity than practicality, I decided to make an electronic whistle blower that could be driven by audio output from any of these practice tools. I had thought through a similar problem in developing the androidomatic keyer, although unlike the androidomatic keyer that was meant to operate without external power (other than the audio signal itself), for this project it was reasonable to use a nominally 12V power source since the contraption would require some kind of air compressor that would have similar power requirements.

The most exotic component in the keyer (aside from the whistle, which is also not typically found in my projects) is a normally closed 12V solenoid valve (Adafruit, #996). This is a brass valve, which is listed as a fluid-control valve, but seems to work just fine for air.  The valve has 1/2″ threads on each side, and I had no problem finding connectors for it at my local hardware store. Per a chart on the Adafruit website, the solenoid draws 3A at 12V. The website also recommends putting a 1N4001 snubber diode across the solenoid leads, so that’s just what I did.

The solenoid is driven by a vox circuit built around a 4558 (741c equivalent) op amp via a STP16NF06 N-channel power mosfet (incidentally, the same one that is used in the Texas Topper QRP amplifier). The top of the MOSFET sticks out of my box because I threw the whole thing together quickly the morning of the contest and didn’t want to bend the transistor down. Also, I wasn’t sure how much heat it would need to dissipate, so I gave it some breathing room.

Compressed air is provided by a 12V air mattress inflator — a glorified waffle fan. These are usually bundled with air mattresses or rafts, but I bought this one as a replacement at Walmart for about $12. The rest of the assembly is a matter of plumbing. I obtained some 1/2″ plastic connectors and modified one to fit onto the pump, and with some careful glue-gunning, embedded a whistle in the other. Originally, I inserted a T-joint and played around with improvised pressure relief valves and/or a balloon to serve as a capacitance vessel because I was worried that the abrupt shut off of flow would strain the compressor. I guess there is enough leakage in the pump itself that this is not a problem, though, because it works fine to simply connect the pump to the solenoid valve. The pump comes with instructions that it should not be used continuously for more than about 15 minutes without some cool-down period. That seemed fine for my application, which is deafening after a few minutes.

I had supposed that morse code sent by whistle would need to be slower than we’re used to hearing on the radio, but as you can see in the demo, the solenoid has no problem keying at a 20 words per minute. I assume that people could achieve a similar effect by tonguing the whistle like a recorder.

We had a good session with the scouts, and the TEAPOT was a hit, leading to a brief discussion of electronic projects, robotics and flame throwers. After our session on morse code, they  popped into the radio room, where the club had already started the NAQP contest, so they also got to see morse code being used to communicate.

Significant Other Update: Logic Board

For a few months, I’ve been playing working on a design for a QRP accessory as a way of becoming familiar with both the arduino platform and homebrewing technique. The basic idea was to put everything except a transceiver in one box, so I couldn’t leave anything behind when operating in the field. I wrote up a design overview when I started, and it is more or less up to date. The schematic isn’t necessarily finalized, but I’ve also posted the most recent version.

The first item I built was a relay board, with latching relays to route the signal through a bank of capacitors and inductors arranged in an L-network, configurable on the fly for low or high-Z. The prototype built on vector board  has nice blinky lights to help me visualize how the relays are switching. I’ve also built a power module and RF module (which senses SWR and reads frequency) on copper clad board.

Over the  New Year’s holiday break, I laid out the logic board, which contains the microprocessor (an ATmega368), a real time clock, LCD display, a piezo buzzer, some buttons, and connectors for paddle input and keyer output. The logic board also sports a USB interface to make my life simpler — I don’t think that will show up in the “final” version, which I envision being laid out as two PCBs: one for control, one for relays.  In the prototype, the two boards are joined by a ten-conductor ribbon cable (with RF connections through shielded cable, not added yet).

The two blank areas on the logic board are where the power module and RF module will be pasted in this prototype. For now, I’m leaving them off and concentrating on the programming aspect of the project. I’ve got some ideas about the global operation of the device and its menu structure, but before I really start any detailed coding, I’d like to look through a few similar projects. An obvious place to start is the full-featured CW keyer described by K3NG at http://radioartisan.wordpress.com/.  I can’t imagine putting all those features into this project, but I think I’ll learn a lot from reading through the code.

Significant Other Power Supply

Initially, I hadn’t given the power supply for the Significant Other project too much thought: I was more focused on the microcontroller, relays, and so on. After going for maximum efficiency with these components, though, it began to annoy me that it would be very wasteful to use an LM7805 regulator to bring lead acid battery voltage (13.8V) down to something that all the chips and relays could use (5V). The LM7805 tosses out the difference in heat, and while at the low currents that I need that doesn’t amount to much power — certainly, not enough to require heat sinks — it goes against the grain of QRP. If you have to haul a battery up a mountain, you’d like it to last as long as it can.

So, I started looking at more efficient (and lighter) means of powering the unit. The design I selected allows for two options. First, two AA batteries will fit inside the unit. Building them into the case assures that I can’t forget them. One of the goals of the SO project is to avoid unpleasant surprises while setting up the station in some remote location.  Since the unit draws so little current, I’d hope that a pair of AA batteries would last quite a while in field use.

Since radios are made to work from 13.8V sources, this is the other acceptable power input. The unit will be built with dual powerpole connectors, so that even if the battery has a single powerpole, it can be plugged into the unit, which effectively replicates the plug, so the radio can also be plugged into the unit. Even if the radio is greedy and pulls power from the battery causing the voltage to sag, the power regulator should cope with anything down to about 7.5V. If the lead acid battery gets that low, it’s probably toast anyhow.

Getting 5V from a 3V source requires a switching power supply, which could be a problem for a radio project since the switching happens at frequencies in the hundreds of kilohertz range. The LT1302-5 chip that I used in this project does not oscillate at a specific frequency, but is variable, and has the potential to produce RFI over a broad range of frequencies.

I followed the datasheet for the 1302 and built a “typical” supply using available parts. Layout is fairly critical, and I did my best to port their suggested PC board layout to manhattan construction. I didn’t have a 20k resistor, so I went with a 22k. I didn’t have any particularly low ESR electrolytics, so I used ones regular ones, etc. It seemed to work anyhow.

For testing purposes, I ran the power supply with a small load next to my FT-187nd, which was connected to a dummy load with cable that was unshielded for several centimeters. Within the ham bands, the only places I heard hash were on 160m and 80m, and even there, it only seemed to be around a couple frequencies. I had originally built the supply with a 10uH commercial inductor wound on a solid core. To limit EMI, I tried replacing this with an equivalent value hand-wound toroid (45 turns of 28Ga on a T50-2). This brought the noise level way down, and I couldn’t hear it when the antenna run was a couple cm away from the toroid. I suppose I could put the power supply in its own metal compartment, but it’s probably enough to just keep the RF path away from it in the layout.

Getting the right combination of bypass and charge-holding capacitors and discharge resistors is a bit empiric, and I’m not sure I did an optimal job, but I got out the voltage that I wanted. When connected to the oscilloscope, I noticed a periodic ~50mV spike that I thought could be a problem down the line for the microprocessor, so I borrowed a low pass filter from a similar project, the power supply in the Norcal 2030. I again had to substitute a bit — I think the filter inductors came out of an old TV. With that filter in place, the voltage is completely smooth as far as I can measure.

The two power supplies are connected by wire “OR”ing them together. The LT1302 senses 5V distal to a Schottky diode, but putting a diode after the higher power supply means that the voltage prior to its diode must be about 5.3 volts. To get that value, I used an LM317 and selected specific resistor values for its feedback network. The LM317 needs a small load to stabilize, so for the prototype, I threw in an indicator LED that lets me know when the high voltage supply is in use.

When the high power supply is active, it pulls up the LT1302 shutdown pin, which turns off the up-conversion. Without all that switching action, the voltage on the toroid side of the diode should be that of the AA batteries. This means that with the higher power supply active, the diode in the lower power supply is reverse biased and no current flows through it. This should mean that the unit can hot-switch between onboard and external power.

The prototype was a little smooshed because I had originally intended to only build the LT1302 circuit on that piece of copper clad board, and then I added the filter, and finally the 13.8V supply.

The real test of this supply will be whether it makes the other components happy.

IF Comp 2012 – Kicker

The kind of kicker with which I am more familiar: from the board game Cosmic EncounterI don’t think that it’s a spoiler to reveal that this is a simulation game, not only of American football, but of what it is like to play the kicker position.

I am bringing a lot of emotional baggage to this review, so in the interest of full disclosure, I should mention that I lived in Buffalo, New York from 1988 to 1997. You can’t live in Buffalo without being a fan of the Buffalo Bills, and you can’t be a fan of the Buffalo Bills without suffering.  In particular, during the period that I was there, the Bills went to the Superbowl four times in a row. And lost four times in a row.

Despite sitting through too many games to count, consuming the yearly output of the sun in suicidally hot Duff’s Wings, nearly freezing to the aluminium benches in Rich Stadium in -40 degree weather, and knowing all the stats on every player during that period, I don’t know the first thing about football… except that Scott Norwood missed the final kick in Superbowl XXV, and to this day, if there is just one thing that I and everyone else who still lives in Buffalo can remember about football, it is that one 47-yard field goal that went sailing to the side of the uprights and cost Buffalo their one true chance at victory.

So, when this story relates that kickers are held in low esteem by their teammates and everyone else in society, I can believe it.

Enough about me… onto the game itself.

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IF Comp 2012 – Sunday Afternoon

Solar flare photographed by sky lab; public domainUnfortunately, I played J’Dal and Sunday Afternoon about a week ago and didn’t write about them immediately, so details probably haven’t stuck with me, but I did make some notes as I went along.

Sunday Afternoon is well written and executed and has a familiar feel to it, so I wouldn’t be surprised to find out that the mystery writer is someone whose previous works I have enjoyed. Or, I might be totally wrong in my guess, so I’ll hold back on publicly guessing the author’s identity.

I put a spoiler break here.

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IF Comp 2012 – Sealed Room

It took some experimentation for me to get this ALAN game to run on my Mac running OS X Mountain Lion. Spatterlight 0.5 exited with an error code. I was also not successful using an older version of Gargoyle under Parallels/Windows XP. The game did work just fine, however, when I downloaded the most recent version of Gargoyle for Mac (http://code.google.com/p/garglk/downloads/list).

If you are expecting an escape-the-room game, this isn’t one in the traditional sense. There is a single room, and there is a way out, but the bulk of this game involves conversation. Unfortunately, the conversation system is limited and the game play is very linear.

More after the cut

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IF Comp 2012 – Murphy’s Law

This is the story of an unlucky, overworked, and mentally exhausted salesman, who is just a single installment shy of paying off a mortgage. The story begins in an apartment scenario, where he needs to write that check, and at first I thought that this might be a three move game. When that turned out not to be the case, I assumed that this would be a game in which minor errors would snowball towards a calamitous end. That’s not quite what happened either.

More after the spoiler cut

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IF Comp 2012 – Irvine Quik and the Search for the Fish of Traglea

It is worth making a special effort to play Irvine Quik and the Search for the Fish of Traglea. For me, it meant downloading the Adrift 4 player and running it under Parallels on my Mac. This story is on par with the best of the parser-based games that I’ve played in this year’s IFcomp, although humor doesn’t always work across broad audience, and this might not suit everyone’s taste. In this story, your back story is impossible,the characters you encounter are strange and your mission ridiculous, but somehow it all works.

All joking aside, there is a lot of structure to this piece. There is a quick bit of exposition at the start: enough to set the tone, but not screen dumps of back story. The game is broken into five chapters, which play seamlessly if you run through them in sequence, but could allow a player to skip around, for instance, to replay a specific chapter.

More after the spoiler break

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