This is just a short set of updates for my weekend projects, meant to keep me in the habit. I’ll write up a more complete version of these projects going forward.
First of all, a new acquisition. My Anet A8 3D printer has proven to be, well, not the most reliable of gadgets. I still haven’t gotten around to fixing its heated bed, but should get to it shortly. But as it happens, a small windfall came my way, so I decided to get a Creality CR-10 which I caught on a good price for less than $400. Unlike the laser-cut, hours-to-assemble Anet A8, the Creality is mostly assembled. It has a 300mmx300mm bed, a much taller range of travel, and is constructed by aluminum extrusions that make for a nice, stiff, and easy to assemble printer. I mostly assembled it in a little less than an hour, but ran out of steam and decided to go to a movie with Carmen and then watch the Superbowl. I’m hoping to print a Benchy when I get home tonight: the only thing I have left to do is get the bed leveled.
I also spent some more time on the ISS clock. I added a new display mode that shows details of upcoming passes, including a diagram of the pass, showing its path across the sky and its maximum elevation. I also updated the epoch that the Plan 13 code was using so that it would be more accurate, and now it compares to within about a degree or so with what other, more sophisticated models have. There are still a couple of lingering glitches. Occasionally it looks for the next pass before the current pass is complete. I suspect that is because I used a number of global variables to communicate between processes, and something in the logic isn’t quite right. But as they say, any program worth writing is worth rewriting. I’ll try to get a version of the code up on github tonight, even though it’s kind of embarrassing.
Stay tuned for CR-10 print experiences and more on the ISS clock.
I haven’t posted an update here recently, but I am (mostly) living up to my New Year’s resolution to spend at least 30 minutes a day working on a project. This has taken the form of some stupid but necessary chores (like fixing the broken pull cord on my lawnmower) but has mostly taken the form of additional incremental additions and improvements to my ISS clock project. This has mostly taken the form of noting a small deficiency, and then working until that deficiency is ameliorated.
The ESP32/Arduino environment still has access to the FreeRTOS operating system below to create tasks, semaphores and queues. I decided that I would implement the program as a set of tasks of different priorities. One task’s job is to compute the current latitude, longitude, altitude and azimuth for the satellite. Another lower priority task scans forward in time, and finds the next time when the satellite rises and sets. When it finds those, it pauses until the current time is beyond the found set time, and then continues searching for the next rise/set pair. The final task runs the display, showing all the current information. If the time of the next satellite rise time (or AOS — Acquisition of Signal) is set, then the display process will give a countdown in hours/minutes/seconds.
This was all working reasonably well, except that I noticed that the time display would frequently “jump” a second, skipping from 42 seconds to 40 seconds in countdown, and sometimes even in the clock display jumping from 10 to 12 seconds for example. I didn’t think any critical path in the code would account for anywhere near that amount of delay in switching between processes, but tried reorganizing the code in various ways to be sure.
In the end, I realized that it had nothing to do with multitasking or the like. I had written code in two different places to convert an internal representation of time used by my Plan 13 satellite library into H:M:S format, and had committed the same error in both locations.
The thing that I realized is that unlike normal Unix time calls, internally my code represents the current time of day as a double which represents fraction of a day. To step the time forward by one hour, I increment that value by 1/24. I have a function whose purpose is to convert this internal representation separate hours, minutes, and seconds.
Here is a (slightly edited) version of my original code.
[sourcecode lang=”cpp”]
void
DateTime::gettime(int &h, int &m, double &s)
{
double t = TN ; // TN is the time in fractions of a day
t *= 24. ;
h = (int) t ;
t -= h ;
t *= 60 ;
m = (int) t ;
t -= m ;
t *= 60 ;
s = t ;
}
[/sourcecode]
The problem appears to be rounding interacting with the timing of the display process. Staring at this code, I’m not sure what I was thinking. I rewrote this code in the following way:
[sourcecode lang=”cpp”]
void
DateTime::gettime(int &h, int &m, double &s)
{
double t = TN ; // TN is the time in fractions of a day
int ts = (int) round(t * 24. * 60. * 60.) ;
s = ts % 60 ;
ts /= 60 ;
m = ts % 60 ;
ts /= 60 ;
h = ts % 24 ;
}
[/sourcecode]
This code works much better. I had coded a similar routine in new code which had the same error. I must admit that I’m still a little fuzzy about how the timing of the display process interacts with this rounding issue to introduce the errors that I observed, but I suspect it has to do with the fact that I inserted delays in the display process to keep that process from updating somewhere around two times a second. I think that the prediction task (which runs for about twenty seconds usually) may be starving the low priority display task just often enough to cause the rounding error to manifest.
I’ll ponder it more later.
Things that are now percolating to the top of my todo list are to understand the event handling of the NtpClientLib library. Occasionally it will toss errors from the WiFiUdp.cpp file, and error handling is not appropriate (sometimes it doesn’t set time properly). I suspect I’ll have to dig into the networking code in the library a bit deeper.
Addendum: The display on this thing is one of those tiny 0.91″ OLED displays. It’s really at the limits of what I can comfortably read, and I’d like to have more space (and potentially color). I have some small 1.8″ LCD boards, but I stumbled across the M5Stack board which appears to be available on banggood.com. It looks like a cool little box.
I ordered it from this link on banggood for about $33. Besides having an ESP32 module, it includes a case, a 320×240 2″ color LCD panel, and three buttons. The larger display size and buttons are a great fit for my ISS project. When it arrives, I’ll quickly work on a port of this code to that.
If that doesn’t work, I’ll probably work on adapting it to some of the ST7735 modules I have lying around that I ordered from icstation.com.
Stay tuned for more progress, and eventually links to the git repository for the code when I am not embarrassed by the code.
Today, I finally lost my freaking mind with respect to Comcast.
First of all, some background. I’ve have been a Comcast customer since 1999 when I moved into my house. For the most part, the service itself has been reasonably reliable and effective. I don’t have a lot of technical quibbles with them.
But their customer service makes me absolutely insane.
I am currently paying $269 a month (yeah, I know, right?) for a combination of Internet, TV, and phone (which I didn’t even want, but which was part of some “package” deal that was supposed to save me lots of money, that somehow never really materialized). I have mostly been ignoring it, but I finally decided that if I am paying nearly $3000 a year on television and Internet, I should review my priorities to reduce my bill since I pay for a lot of premium services that I probably don’t really need.
And here is where my irritation begins.
Because if you want to do that, you can’t do it online. In fact, other than determining that someone, somewhere signed me up for some package which has the label “HD XF Premier Bundle” and a somewhat mysterious “Additional Outlet Fee” for $39.00, it has no indication about what Internet speed limits can be be achieved, what channels are included or not included, and most importantly there is no way to actually determine what my options are. In fact, to make any changes to your service, that means talking to a service representative.
And here is where my absolute rage begins.
I hate losing my temper with people. I really do. I like to be easy going and polite. If someone is trying to help me, I try to help them help me. But Comcast service representatives are not there to help you. They are there to sell their package deals, which seem carefully constructed to be as opaque as humanly possible and to extract the maximum amount of money from you that they possibly can.
It’s infuriating, and today my fuse was admittedly short.
To be fair, I probably wasn’t fair. I wanted to a) review each of the charges on my bill and b) decide in each case whether the charge was appropriate, and what my options might be to change it. But the Comcast service representative literally could not do that. She insisted on trying to tell me that there was some other package, with some other price that she could sign me up for that would achieve some other price that was much cheaper. When I said that sounded better, she asked me whether I wanted to sign up for a “commitment” or not, and started explaining that if I signed up for a commitment, then I could not change my service for two years. And I am supposed to decide all of this without an actual itemization of the terms and conditions or even the services that were provided.
And I lost my freaking mind. Expletives were emitted. I was not a gentlemen. And then something that has never happened before, happened.
I had a customer service representative hang up on me.
So, I’m going to do something truly crazy: I’m ditching Comcast. Sonic.net has become available in my neighborhood, and they have more sensible packages available with Direct TV. I imagine that the service that I am going to get is a bit less speedy than Comcast, but I literally don’t care. I literally don’t care if Direct TV is better or worse than Comcast or even cheaper. I just no longer want to be a Comcast customer, and since it appears I don’t have to, I am not going to.
Voting with my feet. I’ll let you all know how it goes.
LB3RE sent me a link to this awesome HF beacon by Anthony, F4GOH and Christophe, F4GOJ that has many of the same features as my (as yet still in-progress) beacon transmitter does. And, of course, his actually exists, so it’s already infinitely more awesome than my idea.
I was particularly interested in his very simple power amplifier using 4 ganged BS170s. I’m likely to be operating mostly on 30m, so I think I could probably get buy with a single harmonic filter, and I am not imagining that I need all the relay switching, but there is some good information to be mined in there.
I was working on some additional software to power my nascent WSPR project. I’ve been thinking that rather than using an Arduino, it would be better to use the Teensy, so I’ve been experimenting a lot with the Teensy LC. My idea was to wire up my Ultimate GPS and an I2C based DS3231, and then write a sketch that powers up the GPS, attains a fix, and then uses the time to set the time on the DS3231. It then will periodically wake up the GPS and check the time as reported by the DS3231 against the GPS.
But I’m having some difficulty. The GPS part works just fine, but when I try to do the first write to the DS3231 to set the time, it occasionally hangs. The way these libraries are written, the writes never time out, and the exchange grinds to a halt.
I’m not sure what’s going on here. Could be a bug/issue in the library, or something having to do with the Teensy Wire library, or the pull-ups. The rise times seem very slow.
I’ll keep playing around to figure out what the deal is.
Addendum:This seems relevent but the code is only for real Arduinos, and probably needs some tweaks to work with the Teensy. I am curious as to whether the delay itself may be enough to help.
Previously, I wrote about a project I called the Big Box O’ RF. I’ve shifted goals a bit, and done some experimentation, and have changed some of my goals and approach.
First of all, I’ve changed the goal a bit. Instead of being a piece of test equipment, I’m actually more interested in using it to implement a beacon transmitter. It’s been quite some time since I have done any QRSS (slow speed Morse) or WSPR (Weak Signal Propagation Reporter) but I still find it to be a pretty interesting thing to do. What I’ve wanted to have for a while was a dedicated beacon transmitter that didn’t require the cooperation of my laptop and FT-817 to send out a modest signal. It seems to me that this totally doable mostly with parts I have on hand.
Goals:
Output power between 250mw and 500mw
Controlled by an inexpensive microcontroller. While the Arduino would be an obvious choice, the Teensy LC or Teensy 3.1 are as easy to program, and offer some interesting improvements for similar cost.
Able to integrate multiple methods to keep accurate type of time. Initial prototype will probably use the Ultimate GPS I’ve been playing with. Alternatives include clock boards based upon the DS1307 or DS3231, or synchronization via Wifi/SNTP (almost certainly using the ESP8266).
Able to support multiple modes: at least WSPR, DFCW, and Slow Feld.
LCD panel to display information. Text based interface supplied via USB, allowing you to change message, frequency, timing, etc…
RF generated by my AD9850 module.
I’ve been tinkering with most of the modules independently, making sure I can interface with each of them. They all seem to work fairly well. As soon as I find an appropriate box, I’ll start getting them put together. I’ve built a harmonic filter for 30m (where I plan to do most of my operation). I need to work on the amplifier chain, as well as a little transmatch (I don’t want to dedicate one of my antenna tuners to this operation either).
One of the things that I really like about the Teensy LC (besides its low price) is that it has three hardware serial ports. Hardware serial ports are just nicer than the SoftwareSerial ports that you see on the ordinary Arduino platform. While the latest support for SoftwareSerial ports on digital pins work reasonably well at low baud rates, they aren’t especially good or reliable at higher baud rates. The Adafruit UltimateGPS I have supports data output at 10Hz, which requires serial rates of 115200, which isn’t especially reliable.
But I’m still inexperienced with the Teensy. To test my understanding, I wrote this little program for the Teensy LC, after hooking my GPS up to pins 0/1 as RX/TX. Note: the Serial object does not route to any of these three outputs: the Serial object is a distinct USB object that is not mapped directly to digital pins.
This was also an attempt to test the TinyGPS library with the Teensy LC. It worked the very first time I got it to compile.
I’m definitely leaning toward using the Teensy (either the cheaper LC version, or the more expensive but more faster/more capable 3.1, which includes FIFOs for serial ports) on my WSPR project.
[sourcecode lang=”cpp”]
// __
// / /____ ___ ___ ___ __ _________ ____ ___
// / __/ -_) -_) _ \(_-</ // /___/ _ `/ _ \(_-<
// \__/\__/\__/_//_/___/\_, / \_, / .__/___/
// /___/ /___/_/
//
// On the Teensy LC, there are three hardware supported serial ports.
//
// Port Rx Tx
// ——-+–+–+
// Serial1| 0| 1|
// ——-+–+–+
// Serial2| 9|10|
// ——-+–+–+
// Serial3| 7| 8|
// ——-+–+–+
//
// It appears (as yet unverified) that these are distinct from the serial
// port which is connected to the Serial object. This program is designed
// to test that theory.
I hooked up my new DS3231 clock module to an Arduino that was being fed with the one pulse per second input from a locked GPS, and counted the number of pulses from each. In 3170 seconds, the clock module generated 103874565 pulses, for an average pulse per second of 32768.0015773 pulses per second. That’s really good, only about 2 seconds per year. Of course this was a short term test, under relatively stable temperature conditions, but still, I’m highly impressed. I’m thinking that using this to drive my WSPR radio beacon is likely to work out very well.
Greetings readers. I’m hopefully wishing there is still more than one.
This weekend was the Bay Area Maker Faire 2015, the 10th incarnation of an event which has become increasingly (even frighteningly) popular. I’m tempted to channel Yogi Berra, who said “Nobody goes there. It’s way too crowded.” Anyway, I got out of my house around 9:00AM, with the plan of parking at one of the offsite parking lots and shuttling in. It took me about an hour to get to the Oracle lot on 10 Twin Dolphin Drive, and there were already probably six or eight busses lined up, but probably a thousand people lined up as well. As it happens, it took slightly more than an hour to make it onto a shuttle, drive in and enter the gates. Bleh. Not the most fun, but I had a good nights sleep the night before, so I was mostly in good spirits as I entered the park.
It was very crowded. I was by myself, so I just started wandering. When I go to these things, I am mainly looking for three things:
Projects that inspire new projects.
Cool new products, especially inexpensive dev boards and gadgets for future projects.
Cool artwork that I haven’t seen before.
Sadly, I didn’t see a ton of projects that made me think of new projects, but there were a couple. I had a nice chat with Ben Krasnow who brought some low-tech versions of his excellent rheoscopic coffee table, which were just plastic cells that rotated on a lazy susan. You’ve probably seen identical gadgets in science museums. Fluid flow is always interesting. He said the instructions were already on the Make Magazine site, but I forgot to copy the url, and didn’t find it. He also said it would be in the print edition sometime soon.
I had a nice chat with Erin Tomson of Modulo Labs LLC. She’s a former Pixar colleague, who has gone off and created Modulo, a set of pluggable programmable modules that can be used to assemble modules in a tiny, secure network, without the hassle of routing jumper wires on breadboards. (In fact, a system like this would have prevented a lost hour of my time tonight, I’ll tell that story below.) It’s a very slick little system, and I’d like to see something like this take off. I can particularly see this as useful in education.
Check out her Kickstarter video.
I particularly like optical gadgets like telescopes and microscopes. My buddies Rich and Dave from the Chabot Telescope Makers Workshop were there, grinding away and answering questions about telescopes. Nice to catch up with them. They said that quite a few people came up to them and asked “So, you guys sell telescopes?” Sigh. This is the Maker Faire. If you are in the North Bay and want to learn how to build a telescope, click on the link above, and think about attending one of their free workshops (every Friday!).
I like projects which reuse camera phones, and this microscope project seemed pretty cool. They had a little gadget that allowed you to swap out three different lenses to get different magnifications. Their system seemed pretty cool, but the basic idea is pretty simple (in fact, it’s basically a version of Antonie van Leeuwenhoek’s first microscopes, but instead of holding it close to your eye, it’s held close to your cell phone, which can use nifty features like zoom and exposure adjustments, and can of course record video and stills. I should design such a gadget myself.
I also had a nice chat with Alan Yates who was demonstrating some “Lighthouse” technology that he’s been working on at Valve. The basic idea is to create a set of “beacons” that can be scattered around an environment, and a sensor that can (for instance) be mounted on a VR headset and can be used to figure out the position and orientation of the headset with high accuracy and low latency. I don’t have a link for this work yet (did I miss it, Alan?) but when I do, I’ll try to update it.
That was kind of it. I did poke my nose into various people experimenting with aquaponics, which I find interesting. I had a brief chat with the creators of Chip, the $9 computer currently on Kickstarter (I hope to have more information on that soon, stay tuned.) I didn’t spend much time in the “Dark Room”, the noise and flashing gives me a headache. I did spend some time looking at the various gardening and bee keeping exhibits.
And, I did pick up some new gadgets. Here’s a short video of my purchases, along with some links to the various items mentioned.
A Spark.io Particle Photon Kit Spark.io has changed their name to Particle, and then did a deal with Sparkfun to build additional add ons and distribute the Photon. I don’t know a lot about the Photon yet, expect some posts about it in the future.
A little wireless keyboard from dfrobot.com. Hooked it up to my Raspberry Pi in my living room, and it seems to work pretty well. DFRobot appears to have their own line of Arduino clones, including ones that do Bluetooth Low Energy at fairly reasonable prices. Might be worth checking out.
And that’s about it. If anyone thinks I missed something super cool, drop me a comment below and I’ll check it out.
Today, I had a bunch of chores to do, but I did start to play around with my AD9850 project a bit more. Since I spent so much time driving around yesterday, I had lots of time to think, and realized that the code the determined the tuning word (the 32 bit value used to select the frequency of the oscillator) was probably going to not work properly, since it used floating point arithmetic, and that probably didn’t have sufficient precision to do the calculation the way that I had coded. Indeed, when I got home, I hooked up and Arduino and found that I was not getting the sub-Hz spacing that I requested. I played around with the math a little bit, and got it working better, and then set it up and started it going. I had the output of the AD9850 going into my oscilloscope, so I could monitor the waveform.
And it was glitchy. Intermittent. Not working properly. Had I made a programming mistake?
I spent the better part of 45 minutes trying to understand how I had broken the program. Nothing made sense. I was cranky. I decided to step back and go buy some cat litter than I had forgotten, and give it a rest.
And of course when I got back, I stared at the board again. And it was immediately obvious. I had the AD9850 module on a breadboard, with all the RESET/CLOCK/LOAD/DATA lines going to the Arduino. And… that was it…
There was no common GND. I had somehow tugged out that little jumper wire. Without a common ground, it was surprising that there was any communications between the module and the Arduino.
Plugged it back in and voila. All works. Sigh. An hour of my life, wasted.
Yesterday, I mentioned the idea of using the cheap ESP8266 as a clock source for a WSPR beacon transmitter. My initial idea was to basically write code for the Arduino that connected to a remote NTP server, formulate UDP packages… sounds like a pain. But then I found that there was alternative software I could upload to the ESP8266 that would implement the NTP client on the ESP8266 module, and then simply fetch it with an “AT” style command.
So, I downloaded the firmware, and gave it a shot.
I rebooted, and then told it to connect to my local wifi network, and then told it to start the NTP client with the following commands…
AT+CWJAP="ssid","password"
OK
AT+CIPNTP=0
And it works! I can get this connected to the Arduino and write up a simple sketch, and it should be able to update the time really easily. This is cheaper and probably easier than using a GPS as a time source. Very cool.
Yesterday I finally found a copy of the code that I wrote years ago to figure out the tone sequence for messages used by the Weak Signal Propation Reporter system. To avoid losing it again, I decided to put both the C versions and the Python versions on my github page so that even if my servers go down I’ll have the code archived somewhere. If you have need of the code, feel free to use it (it would be nice if you gave an attribution in any derivative works that you distribute, but I won’t go so far as to insist).
When I got home, I found myself thinking about using the AD9850 as a WSPR beacon, using an Arduino (or similar) to generate the tone sequence, telling the AD9850 to switch to those frequencies, and generate the appropriate RF. This was basically a meld of two programs: the genwspr.c code that I listed above, and a simple sketch that can be used to set the AD9850 to different frequencies. It seemed very simple, so I sat down and started tinkering.
I began by copying the genwspr.c program into a new wspr.ino sketch. It pretty much would compile as is (after I added the necessary dummy setup() and loop() entry points needed by the Arduino) but it did not generate the same code sequence as the code did when I ran it on my desktop. A moment’s thought revealed the likely cause: “int” values are only 16 bits on the AVR. It actually took me a bit of time to get the types sorted out (maybe 30 minutes), mostly because I didn’t remember that I should use (1UL< <n) instead of just (1<<n) to get the needed 32 bit values.
Once I got that sorted out, I extracted the needed “setFrequency” routines from an AD9850 sketch, and created a loop that would send the different frequencies at the right time. The four tones needed by WSPR are 12000/8192 (or about 1.465 Hz) apart and are 8192 / 12000 seconds in duration. My initial code simply calculated the frequency for the the given message entry, sent the appropriate tuning word to the AD9850, and then called delay(8192/12) (delay uses microseconds). Because that didn’t take into account the time spent calculating and setting the tuning word, the overall message was a bit long (actually only 22ms long) so instead I did a delay(8192/12-1), and then a delayMicroseconds(22000/162). That put it right at the 110.592 seconds that are specified. (I know it’s silly, the clock in the Arduino could easily be off, but I thought it would be good to be tidy. If you had source to an accurate 1PPS source, you could do a better job of this).
I was a tiny bit concerned that the tuning resolution of the AD9850 was insufficient, but consulting the datasheet, the nominal resolution is about 0.029 Hz. That should be fine. I’ll dig out my SDR-IQ this weekend and try to do some workbench reception tests over the next few days.
The next bit you need to make a functioning beacon is to ensure that the transmissions start one second after even minutes. That requires some accurate time keeping. My initial idea was to hook up an old Parallax PMB-648 GPS module that I had lying around. During slots where it wasn’t transmitting, it could use the time signal from the GPS to ensure that the clock had not drifted. I hadn’t played with this module in a while (it’s listed as obsolete on the Parallax page) so I hooked it up to the Arduino, wrote a simple sketch to read data from it, and let it run.
Frown. It’s just not sensitive enough to get a lock while inside my house. I thought about alternatives for mounting it. Grumble. Didn’t like that idea. External antenna? Newer module? Grumble.
Perhaps a different approach was needed. I considered the various wireless modules that I had lying around. Perhaps I could use the esp8266 modules (which are really cheap) to fetch the time with NTP, and then the Arduino could use that to trigger the transmissions.
Hooking the ESP8266 to the Arduino is not quite as straightforward as the GPS because the Arduino that I use is 5V, and the ESP8266 is a 3.3v device. I have some Sparkfun level converter boards around, but it turns out that you really only need to be careful about the TX from the Arduino. The circuit below uses a little 3.3V Zener diode to drop the voltage to avoid blowing the URXD on the ESP8266. I think I have some 3.3V zeners in my box somewhere. The circuit shows a separate 3.3V low drop out regulator because the ESP8266 can be quite power hungry, and the regulator on your traditional Uno can only supply about 50ma. I believe the Redboard has a better regulator, the MICREL MIC5205 LDO can supply 150ma, so that should be fine. If I can find the Zeners, it should be easy to breadboard.
My idea was to use the ESP8266 to send out NTP packets, parse the results… but a little googling revealed a better way. There is alternative firmware for the ESP8266 that adds support for NTP directly via AT commands. If you send the AT command below, you’ll get the time back:
AT+CIPNTP?
Time: 22:22:42 12/02/2014 GMT+02
That seems awesome. The idea will be that when the Arduino is reset, it will bring up the network and try to get the time and will figure out when the next time slot begins for transmission. When that slots begins, it can decide to either transmit, or wait until the next slot. Easy-peasy.
When I get the completed sketch up, I’ll add it to my github respository.
I tinkered together a circuit for a buffer amplifier that I thought would be good to use with the AD9850 DDS board I have. In particular, for the purpose of this exercise, I was trying to preserve the nice sine-wave nature of the DDS input, and present it at the output into a 50 ohm load. I dug around and ended up creating this circuit in LTSpice.
(I didn’t do the design, it was from my notes, but I failed to crib where it originally came from.)
I know it is is ridiculous to look at this from the standpoint of efficiency, but this feedback amp is astonishingly inefficient. Overall power draw averages at 470mw, with only 2.6mw of power actually delivered into the 50 ohm load. That seems pretty ridiculous in terms of efficiency.
Surely there must be a better way (power wise) to preserve the original waveform over a large range of possible output frequencies, yes? Or maybe not. I feel like understanding this is one of those teaching moments for me.
As I’ve mentioned over the last few months, I have piles of different development boards, and lots of little display modules and the like. I’ve been thinking of doing a simple radio project, aimed at helping further experimentation with QRP (low-power) radio homebrewing. Inspired by Pete and Bill over at the Soldersmoke Podcast, I thought that I might use a dev board to build a gadget which I am calling:
The Big Box O’ RF
The idea is to take an Arduino (or maybe Teensy?), and connect a couple of different peripherals to it that can generate RF. I have both an AD9850 DDS module:
And one of Adafruit’s Si5351 boards, which are cool because they can generate three different outputs at once, under I2C control:
I also have one of Jason’s (NT7S) little Si5351 kits that I could assemble:
And of course I have a bunch of I2C display peripherals, some rotary encoders, and various power jacks. All I really need would be a nice aluminum box, and I could assemble a general purpose signal source/VFO that I could use in experiments.
Sounds pretty cool, yes?
Well, I have a few details to work out:
I’m envisioning a front panel which has a bunch of panel mount connectors that I can attach coax pigtails to route RF to my various project. (Probably 4, one for the AD9850, and three for outputs from the Si5351). The (semi) obvious choice would be SMA female panel connectors, and use pigtails to inject the RF into various other projects. Does anyone have any recommendations for where to get reasonably inexpensive SMA male-male pigtails? Is there a better (read cheaper) alternative that could be used? I’ve used Type F or even RCA jacks before, is that stupid?
Inside the box, would you use RG174 or RG316 to carry RF signals from the board outputs to the panel mounts? Any hints on shielding?
Should I make a buffer amplifier for the outputs? Or low pass filter modules (switchable?)
This project doesn’t need to be perfect, but it would be nice if it was good enough to serve as test equipment that I would want to keep on my desk. Anybody have any ideas?
Addendum: This box built by Bob, WV2YAU seems close to what I have in mind:
I was originally licensed under the callsign KF6KYI (Kenwood-Yaesu-Icom, or what I prefer, Kiss Your Iguana) but when I upgraded to Extra a few years back, I dug around and was lucky enough to snag the callsign K6HX (missed out on getting the highly desirable K6TT, which would have been AWESOME). I never really gave it much thought. I remember looking up the history of the call, and finding that it was previously held by something called the “Lew Stoner Memorial DX Club”, with Donald Stoner, W6TNS listed as the club trustee. Both his call and the club call (along with a second one called the Lew Stoner Memorial DX Club East W8IMS) had expired, so I hypothesized that this gentleman had become a silent key, and nobody had stepped forward to claim his call or renew the club calls.
Tonight, I dug a little deeper, and found something interesting that I did not know.
No doubt some of you are familiar with Don. He is perhaps most famous for being the guy who first dreamed of the OSCAR: which stood for Orbiting Satellite Carrying Amateur Radio. He laid out a vision for the program in a February, 1961 article for QST magazine (if you are a member of the ARRL, you can download a copy). In it, he lays out the vision of a satellite beacon, and a later satellite repeater that could be operated and worked by radio amateurs on the 2m band. It’s a very cool article, and of course now 50+ years later, amateurs achieved all he dreamed of and more. In it, he mentions that he would publish the circuit for a beacon transmitter that could be built by amateurs for “less than $15”, but as near as I can tell, that article was never published.
I was not able to find any references to “Lew Stoner” or to any activities by the DX Club which bears his name. Does anyone else know any more information?
AMSAT is excited to announce that we have accepted an opportunity to participate in a potential rideshare as a hosted payload on a geostationary satellite planned for launch in 2017. An amateur radio payload, operating in the Amateur Satellite Service, will fly on a spacecraft which Millennium Space Systems (MSS) of El Segundo, CA is contracted to design, launch, and operate for the US government based on their Aquila M8 Series Satellite Structure.
This would be very exciting. The only satellites I’ve worked have really worked with any regularity have been the FM satellites in low earth orbit. I’d love to have an opportunity to develop a station to work a bird in geostationary orbit. I’ll be watching this closely, and probably kicking in some donations to AMSAT-NA to grease the skids.
