Hook an antenna to your Propeller, and listen to the radio! (New shortwave prog
Phil Pilgrim (PhiPi)
Posts: 23,514
Okay, the title's a bit of a come-on, since it's not a very good radio; but it's an AM radio, nonetheless, with digital tuning to boot. Moreover, it can be built without any additional active components. If you have a Propeller Demo Board, a resistor, cap, inductor, wire antenna, and a decent ground are all you need.
THEORY
Now that I've got your attention, here's the theory behind it. Most consumer radios on the market are superheterodynes. In such receivers, the incoming RF signal is "mixed" with a sinewave coming from a tunable local oscillator (LO). Mixing is basically analog multiplication, which produces, in addition to the original RF and oscillator signals, signals which are at both the sum and difference frequencies of the two. The output of the mixer is filtered to a single, fixed, "intermediate frequency" (IF) and then amplified. In AM (amplitude modulation) broadcast radios, which tune from 550KHz to 1600KHz, the IF is usually at 455KHz. So, by varying the frequency of the local oscillator from 1005KHz to 2055KHz, one can obtain a 455KHz difference signal from the mixer for the entire broadcast band. The output of the IF amplifier is then introduced to a "detector", which rectifies and low-pass filters the IF signal to produce an audio waveform.
A receiver similar to the superheterodyne is the direct conversion receiver. In such a receiver the "intermediate frequency" is zero. In other words, the LO is tuned to the exact frequency you want to listen to, and the difference signal is simply the detected audio, which can then be lowpass filtered and amplified. But there's a catch: the local oscillator must not only have the same frequency as the desired signal, it must also have the same phase. To understand this, suppose the incoming RF carrier and the LO were 90° out of phase with each other. When multiplied together, these two signals would effectively cancel each other out, and you'd hear nothing. When they're in phase, the positive swings would multiply, returning positive results, and the negative swings would multiply, also returning positive results. But getting the LO to lock onto an incoming carrier can be tricky — especially if that carrier is weak.
One way around this is to have two LOs, 90° out of phase with each other, and two mixers. The idea is, what one LO oscillator misses by having the wrong phase, the other will catch. In fact, the outputs from the two mixers can be combined in such a way that the actual LO phases are irrelevant, so long as they're 90° apart. The formula for doing so is:
····Audio Amplitude = sqrt(I2 + Q2),
where I is the output of one mixer (from the "In-phase" LO), and Q is the output of the other mixer (from the "Quadrature-phase" LO).
Well, that's enough theory to lay the groundwork for the Propeller receiver. I've really glossed over a lot of stuff, but this is a forum post, not a book, and I want to get to the actual hardware and software.
APPLICATION
The use of a Propeller counter as the basis for an analog-to-digital converter (ADC) is now well-established. So why not simply attach an antenna to the input of one of these ADCs and see what comes out? Basically, that's what I've done. Here's a schematic:
The antenna (a wire strung across the ceiling of my shop) is connected, through an inductor to both digital ground and earth ground. I used a 330uH power inductor I found in my junkbox. It actually worked better than the ferrite antenna scavenged from a cheap transistor radio. A bunch of enameled wire wound on a plastic sewing machine bobbin worked almost as well, too. I'm sure Beau Schwabe (i.e "He Who Understands Inductors and Knows What to Do with Them") can shed a lot more light on the choice of inductors and why one is needed here. I just grabbed what I had until I found something that worked. My "earth ground" consists of the ground clip from my scope attached to the ground stud on the Demo Board. My scope input return ground and its AC protective ground are connected together, thence back to the breaker box and to a metal grounding rod. (By the way, I live in a fringe area for AM reception. If you live in a city with strong AM transmitters, you may not have to go to all this trouble.)
The antenna also connects, through a capacitor, to pin A3 of the Propeller. This is the "analog" input terminal. The feedback comes from A4 through a 470K 0805 SMD resistor, which I soldered between pins A3 and A4 right on the chip itself. I've omitted the usual filter caps to Vdd and Vss (Gnd), choosing instead to let the inherent input capacitance of A3 do the filtering. This keeps both the input impedance and frequency response of the ADC high, which is necessary for detecting weak RF signals. During positive swings of an incoming signal, A4 will be sending more 0s than 1s to counterbalance it; during negative swings, more 1s than 0s. One counter can do this, set up in the "positive-with-feedback" special analog mode. Unlike the usual ADC usage, though, we're never going to read this counter again. It's just that string of 1s and 0s fed back from A4 that we're interested in.
I love the Propeller's counters! I don't know if Chip knew what all could be done with them when he designed them, or if he just had an inkling that, with the right set of features, almost anything could be accomplished. In any event, the counters make ideal local oscillators and mixers! The oscillator part is pretty easy: just configure two counters as numerically-controlled oscillators (NCOs) in quadrature with each other. The frequency will be the frequency of the station you want to tune in. So, if I want to receive KIXI 880 in Seattle, I set up both counters to output 880KHz square waves, 90° out of phase with each other (i.e. PHSB = PHSA + $4000_0000).
Now comes the magic part: the mixers. The counters can be configured to count up whenever two inputs satisfy a Boolean conditional. The Boolean equation can be anything you want: AND, OR, NAND, NOR, XOR, you name it. I used XOR. Each "mixer" counter gets two inputs: the feedback from A4 and one of the LO outputs. If the LO output is low when A4 is feeding back 1s, predominantly (i.e. when the antenna signal is low), the counter will count up at a fast clip. Likewise, if LO is high when A4 is feeding back 0s, predominantly, the counter will, again, count up at a fast clip. In other words, the counter will count up faster when an incoming RF signal is in phase with the LO than when it's not. Moreover, the rate at which it counts up will be proportional to the amplitude of that signal. So, to read the amplitude of a signal in phase with the LO, one need only zero the mixer counter, wait awhile, then read it to see how far up it counted. On average, there will be as many increments during the sample period as non-increments, so the mean (average) count will be half the number of system clocks occurring during the same period. Any signal that's out of phase with LO, or of a different frequency, will contribute as many increments as non-increments, thus having no effect on driving the net count away from the mean.
Therefore, after each sample period, we can subtract the actual count from the mean count to get the instaneous amplitude of the signal. By doing this for both the I mixer and Q mixer, squaring the individual amplitudes, adding them, and taking the square root, we get the signal's amplitude, which can then be fed to the audio output: another counter in DUTY mode, feeding a lowpass filter. (I used A10 on the Demo board, which has the filtering hardware already in place.)
The length of the sample period will affect two things: the audio frequency response and the signal-to-noise ratio. Like most things in life, each of these two desirable qualities increases at the expense of the other, so you have to strike a balance. I got the most pleasing results with a 16KHz sample rate, which yields an 8KHz audio bandwidth. This is about as good as AM radio audio can get anyway, since the stations are spaced 10KHz apart. You can lower the sampling rate to get less static, but the audio starts to sound more "boomy".
SUMMARY
To summarize, the receiver uses six counters (spread over four cogs), as follows: (1) ADC (actually just a digitizing RF amplifier), (2) Local Oscillators in quadrature, (2) Mixers, and (1) Audio Output. Here's a block diagram:
The counters do virtually all the work. There's not a lot of code required, outside of setting up the counters, reading them, and shuffling data between them via the hub. The attached program is configured as a scanner for the AM broadcast band. It increments continuously by 10KHz steps from 550KHz to 1600Khz, pausing at each frequency for three seconds, which is long enough to tell if something's there. It displays the frequency on a TV monitor, via tv_wtext (included). I've also used it for LF reception below the broadcast band with some minor success. As I stated in the intro, it's not a very good receiver — in fact it sounds pretty crappy and noisy. If, like me, you live in a fringe area, you may be disappointed by its performance. But, even then, it does illustrate the capabilities of those amazing Propeller counters. And that, really, was the main point.
-Phil
Update: Owing to advice received from Beau Schwabe, based on his own testing, I've changed some component values. The inductor is now 500uH; the feedback resistor, 10M; the coupling cap, 0.047uF; and the antenna, a 2-meter-long vertical wire. The attached schematic reflects these changes, which did lead to an improvement in performance.
Also, I've corrected a bug in the program's square routine. The bug should have had no effect on the small values involved, but could cause trouble if adapted for other uses.
In a later post (17 Aug 08), I show how to wind the required inductor using readily-available parts. There's also a photo of the complete setup, with a detailed look at the feedback resistor.
Post Edited (Phil Pilgrim (PhiPi)) : 6/11/2010 11:11:36 PM GMT
THEORY
Now that I've got your attention, here's the theory behind it. Most consumer radios on the market are superheterodynes. In such receivers, the incoming RF signal is "mixed" with a sinewave coming from a tunable local oscillator (LO). Mixing is basically analog multiplication, which produces, in addition to the original RF and oscillator signals, signals which are at both the sum and difference frequencies of the two. The output of the mixer is filtered to a single, fixed, "intermediate frequency" (IF) and then amplified. In AM (amplitude modulation) broadcast radios, which tune from 550KHz to 1600KHz, the IF is usually at 455KHz. So, by varying the frequency of the local oscillator from 1005KHz to 2055KHz, one can obtain a 455KHz difference signal from the mixer for the entire broadcast band. The output of the IF amplifier is then introduced to a "detector", which rectifies and low-pass filters the IF signal to produce an audio waveform.
A receiver similar to the superheterodyne is the direct conversion receiver. In such a receiver the "intermediate frequency" is zero. In other words, the LO is tuned to the exact frequency you want to listen to, and the difference signal is simply the detected audio, which can then be lowpass filtered and amplified. But there's a catch: the local oscillator must not only have the same frequency as the desired signal, it must also have the same phase. To understand this, suppose the incoming RF carrier and the LO were 90° out of phase with each other. When multiplied together, these two signals would effectively cancel each other out, and you'd hear nothing. When they're in phase, the positive swings would multiply, returning positive results, and the negative swings would multiply, also returning positive results. But getting the LO to lock onto an incoming carrier can be tricky — especially if that carrier is weak.
One way around this is to have two LOs, 90° out of phase with each other, and two mixers. The idea is, what one LO oscillator misses by having the wrong phase, the other will catch. In fact, the outputs from the two mixers can be combined in such a way that the actual LO phases are irrelevant, so long as they're 90° apart. The formula for doing so is:
····Audio Amplitude = sqrt(I2 + Q2),
where I is the output of one mixer (from the "In-phase" LO), and Q is the output of the other mixer (from the "Quadrature-phase" LO).
Well, that's enough theory to lay the groundwork for the Propeller receiver. I've really glossed over a lot of stuff, but this is a forum post, not a book, and I want to get to the actual hardware and software.
APPLICATION
The use of a Propeller counter as the basis for an analog-to-digital converter (ADC) is now well-established. So why not simply attach an antenna to the input of one of these ADCs and see what comes out? Basically, that's what I've done. Here's a schematic:
The antenna (a wire strung across the ceiling of my shop) is connected, through an inductor to both digital ground and earth ground. I used a 330uH power inductor I found in my junkbox. It actually worked better than the ferrite antenna scavenged from a cheap transistor radio. A bunch of enameled wire wound on a plastic sewing machine bobbin worked almost as well, too. I'm sure Beau Schwabe (i.e "He Who Understands Inductors and Knows What to Do with Them") can shed a lot more light on the choice of inductors and why one is needed here. I just grabbed what I had until I found something that worked. My "earth ground" consists of the ground clip from my scope attached to the ground stud on the Demo Board. My scope input return ground and its AC protective ground are connected together, thence back to the breaker box and to a metal grounding rod. (By the way, I live in a fringe area for AM reception. If you live in a city with strong AM transmitters, you may not have to go to all this trouble.)
The antenna also connects, through a capacitor, to pin A3 of the Propeller. This is the "analog" input terminal. The feedback comes from A4 through a 470K 0805 SMD resistor, which I soldered between pins A3 and A4 right on the chip itself. I've omitted the usual filter caps to Vdd and Vss (Gnd), choosing instead to let the inherent input capacitance of A3 do the filtering. This keeps both the input impedance and frequency response of the ADC high, which is necessary for detecting weak RF signals. During positive swings of an incoming signal, A4 will be sending more 0s than 1s to counterbalance it; during negative swings, more 1s than 0s. One counter can do this, set up in the "positive-with-feedback" special analog mode. Unlike the usual ADC usage, though, we're never going to read this counter again. It's just that string of 1s and 0s fed back from A4 that we're interested in.
I love the Propeller's counters! I don't know if Chip knew what all could be done with them when he designed them, or if he just had an inkling that, with the right set of features, almost anything could be accomplished. In any event, the counters make ideal local oscillators and mixers! The oscillator part is pretty easy: just configure two counters as numerically-controlled oscillators (NCOs) in quadrature with each other. The frequency will be the frequency of the station you want to tune in. So, if I want to receive KIXI 880 in Seattle, I set up both counters to output 880KHz square waves, 90° out of phase with each other (i.e. PHSB = PHSA + $4000_0000).
Now comes the magic part: the mixers. The counters can be configured to count up whenever two inputs satisfy a Boolean conditional. The Boolean equation can be anything you want: AND, OR, NAND, NOR, XOR, you name it. I used XOR. Each "mixer" counter gets two inputs: the feedback from A4 and one of the LO outputs. If the LO output is low when A4 is feeding back 1s, predominantly (i.e. when the antenna signal is low), the counter will count up at a fast clip. Likewise, if LO is high when A4 is feeding back 0s, predominantly, the counter will, again, count up at a fast clip. In other words, the counter will count up faster when an incoming RF signal is in phase with the LO than when it's not. Moreover, the rate at which it counts up will be proportional to the amplitude of that signal. So, to read the amplitude of a signal in phase with the LO, one need only zero the mixer counter, wait awhile, then read it to see how far up it counted. On average, there will be as many increments during the sample period as non-increments, so the mean (average) count will be half the number of system clocks occurring during the same period. Any signal that's out of phase with LO, or of a different frequency, will contribute as many increments as non-increments, thus having no effect on driving the net count away from the mean.
Therefore, after each sample period, we can subtract the actual count from the mean count to get the instaneous amplitude of the signal. By doing this for both the I mixer and Q mixer, squaring the individual amplitudes, adding them, and taking the square root, we get the signal's amplitude, which can then be fed to the audio output: another counter in DUTY mode, feeding a lowpass filter. (I used A10 on the Demo board, which has the filtering hardware already in place.)
The length of the sample period will affect two things: the audio frequency response and the signal-to-noise ratio. Like most things in life, each of these two desirable qualities increases at the expense of the other, so you have to strike a balance. I got the most pleasing results with a 16KHz sample rate, which yields an 8KHz audio bandwidth. This is about as good as AM radio audio can get anyway, since the stations are spaced 10KHz apart. You can lower the sampling rate to get less static, but the audio starts to sound more "boomy".
SUMMARY
To summarize, the receiver uses six counters (spread over four cogs), as follows: (1) ADC (actually just a digitizing RF amplifier), (2) Local Oscillators in quadrature, (2) Mixers, and (1) Audio Output. Here's a block diagram:
The counters do virtually all the work. There's not a lot of code required, outside of setting up the counters, reading them, and shuffling data between them via the hub. The attached program is configured as a scanner for the AM broadcast band. It increments continuously by 10KHz steps from 550KHz to 1600Khz, pausing at each frequency for three seconds, which is long enough to tell if something's there. It displays the frequency on a TV monitor, via tv_wtext (included). I've also used it for LF reception below the broadcast band with some minor success. As I stated in the intro, it's not a very good receiver — in fact it sounds pretty crappy and noisy. If, like me, you live in a fringe area, you may be disappointed by its performance. But, even then, it does illustrate the capabilities of those amazing Propeller counters. And that, really, was the main point.
-Phil
Update: Owing to advice received from Beau Schwabe, based on his own testing, I've changed some component values. The inductor is now 500uH; the feedback resistor, 10M; the coupling cap, 0.047uF; and the antenna, a 2-meter-long vertical wire. The attached schematic reflects these changes, which did lead to an improvement in performance.
Also, I've corrected a bug in the program's square routine. The bug should have had no effect on the small values involved, but could cause trouble if adapted for other uses.
In a later post (17 Aug 08), I show how to wind the required inductor using readily-available parts. There's also a photo of the complete setup, with a detailed look at the feedback resistor.
Post Edited (Phil Pilgrim (PhiPi)) : 6/11/2010 11:11:36 PM GMT
600 x 372 - 14K
453 x 454 - 5K
Comments
We experimented with the Propeller on the Technical University of Budapest. Unfortunately, the synthesiser of the propeller is very noisy.
Now I ordered an AD9951 DDS chip (sample) from Analog Devices.
Would it be possible to produce right radio reception with the DDS and a 90 degree phase shifter according to his opinion?
Leslie
edit:
I haven't done enough to have the noise yet but I hope I think of a way to stop the noise.
Also thanks for reminding me about the other chip just in case it is needed.
Post Edited (VIRAND) : 8/14/2008 8:09:43 AM GMT
I planned a logo last year to a similar project. I asked in e-mail the Parallax's officers, that I am allowed to use this logo for the project.
They were glad that somebody deals with this topic very much. Allowed the usage of the logo!
Let you make use of it for this work if he believes it in that manner.
Leslie
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Rgds, David
At first thought I'm not so sure you'll be able to input the I/Q output from your 9951 to the propeller and have it work as a local oscillator in Phil's technique, the pins have to be sampled and I think this may introduce phase noise (jitter). However, there's nothing to prevent you from using the 9951 to mix externally using a Quadrature Synchronous Detector (QSD), or "Tayloe Mixer" as it's often called. The resultant baseband I/Q would be applied to the propeller via A/D converters, then the propeller can perform the DSP and output demodulated audio data to a D/A, etc.
There's a board and a kit of parts available for your 9951, it even has a quadrature synchronous detector and generator on-board already (good to about 70 MHz), look here:
www.wb6dhw.com
At the same site is a new 9912 controller board. There's a group dealing with these DDS controllers (and more) here:
groups.yahoo.com/group/dds_controller/
You might want to consider Silicon Labs' [noparse]/noparse][url=http://www.silabs.com]www.silabs.com[/url Si570 or Si571 programmable VXO/VCXO instead of the 9951. It is simple to deal with, programs over I2C, has superb phase noise performance and no significant spurious products (unlike the 9951 DDS). However there is no direct I/Q output from the Si570/571, but you can use a simple circuit using two flip-flops to generate I/Q clock output at Fout/4; see the attached drawing.
There is a board and a link for a group buy for the Si570/Si571 at the WB6DHW site mentioned above as well. For best performance, I recommend you use the LVDS version of the Si570 and then convert to CMOS with a Fairchild FIN2002 LVDS/CMOS translator. This is not to say the CMOS version of the Si570 is poor, the LVDS version is only slightly better, and most CMOS versions available to buy have +/-50ppm stability over full temperature range while the LVDS version is +/-20ppm.
There's more information available on the Si570 (including an alternative controller board) at the following group. You may also buy Si570's, controller boards etc. at this group:
groups.yahoo.com/group/softrock40/
Good Luck, David
I say thank you for the hint!
My first idea was a radio receiver (with I/Q demodulator) with the internal synthesiser of the Propeller. The inner synthesiser a lot imply additional noise. Anyway distinguished, but not radio onto an aim it was planned.
My second idea: an AD9951 generates the stable sinus oscillator signal. This signal is going onto a phase-shifter, in the output the quarter of the frequency and 90 degre phase shift. A mixer would get here, and the IQ sign onto the A/D converter. The digital output of the mixer (and A/D converter) circuit gets into the Propeller.
Effectively the propeller only a I/Q demodulator with FFT. Beside this controls the AD9951 DDS chip.
I think, it would be possible to achieve very clear radio reception with this solution in USB/LSB/CW/FM and other modes.
Leslie
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
Very cool! I too live in a fringe area, but I have a decent antenna set up, along with a tapped coil/cap rig for tuning. I'll give this a shot later.
Jonathan
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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
Your article is to be commended - great block diagram, schematic and theory of operation. This is a great educational project!
I remember building crystal sets in primary school - some fitted in matchboxes and some in shoe boxes. They were all great fun and learning experiences - this will be too - and keep kids out of trouble to boot!
Yes, your diagram is close, I think you get the idea. The QSD is external to the propeller as are the A/D and D/A. You will likely need a low pass filter after the D/A. You have four inputs to the QSD from your four-phase shifter. For a digital QSD, you can use only two 90 degree quadrature square wave inputs at the receive frequency. The dual flip-flop I/Q clock generator circuit in my last post does this from a source that's four times the receive frequency.
Study the Fairchild FST3253 data sheet for-example keeping in-mind that you are putting quadrature waveforms into the clock pins as per a schematic like the one attached to this message, make a timing diagram and follow how the switch commutes. The schematic attached is for an actual direct-conversion SDR kit you can buy for around $45 USD (see the softrock URL in my previous post in this thread). The schematic uses the Fairchild FST3253 with the flip-flop clock generator and Si570 for the local oscillator (CMOS version included in kit).
I don't want to hijack Phil's thread with a general discussion on SDR hardware. I sent you a Personal Message (PM) on this forum with my email address should you wish to discuss this further.
Best Regards, David in Jakarta
Neat project!! ... and thanks for the comment "He Who Understands Inductors and Knows What to Do with Them"
It's funny, that while I was on vacation on the coast of Lake Michigan, I was working in Parallel apparently with what you were doing, but you beat me to it. lol
I knew what needed to be done, but did not get my head around a solution in code... Nice work!
Without going into a huge amount of detail... since the 330uH is by itself and not in parallel with an external capacitor to form an LC tank circuit (excluding the inductors self-capacitance) we will look at the impedance based on the frequency.
For the frequency range of 550kHz to 1600kHz the impedance of the 330uH inductor varies from 1.14K to 3.32K
reference:
http://www.cvs1.uklinux.net/cgi-bin/calculators/ind_imp.cgi
The Length of the Antenna also makes a difference and contributes an LC component to the impedance value above to form an RLC tank.
You can get much better results and use a much smaller antenna if you use an RF transformer (two closely coupled coils or a single tapped coil) with a Capacitor to match the resonant frequency to something like 1100kHz (<-- approximate middle of the AM dial) and use that in place of your 330uH coil. The impedance of the antenna should also be matched to the RF transformer.
Edit: Actually a 63pF capacitor in parallel with the 330uF inductor would be "tuned" to about 1100kHz but there wouldn't be a good way to couple your antenna to it unless you could wind a few (2-5) turns of wire around the outside of the inductor... one end tied to ground, and the other tied to your antenna.· At first I would try a variable capacitor that is within·63pF +/- 10 pF at least, but you may find a fixed value that works well also.· In this case we would not necessarily want a high 'Q' value for the coil, and or the cap, so a·5 to 10·Ohm resistor in series with the capacitor might also benefit.· What happens with a high 'Q' is that it becomes·a narrow band tuner, and you may loose other stations.· To be able to tune the other channels digitally, we want a little bit of padding here, so a wider band·tuner is more desirable.
I built your circuit, and used a 500uH coil instead of a 330uH (1.73K to 5.03K impedance) ... I also used a 10Meg resistor for the ADC instead of the 470K resistor. This helps
to provide less loading on the antenna from the feedback I/O pin, allowing weaker signals to be picked up.
With 22 gage solid wire, I used a 6-foot piece of it for my antenna. The attached wav file is the result from a radio station a little more than 9 miles from my home.
Other useful references:
http://www.consultrsr.com/resources/eis/induct5.htm
http://www.powerstream.com/Wire_Size.htm
http://www.daycounter.com/Calculators/Whip-Antenna-Design-Calculator.phtml
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 8/15/2008 5:02:55 PM GMT
One thing I'd like to come up with is an easy-to-fabricate coil (or transformer) with your recommended values, made solely from hardware store and/or Radio Shack materials. I have a real aversion to winding coils that likely harkens back to childhood fumblings with fine enameled wire and empty toilet paper spools. I'm sure I'm not alone in this, so making this part easier will make the project more approachable for those who are more comfortable with digital design and programming.
-Phil
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'Still some PropSTICK Kit bare PCBs left!
Complain about coil winding when you have some 2mm ID, bobbinless coils wound from 0.02mm (~1/1000") wire under your belt (and under the desk and behind the sofa) [noparse]:)[/noparse]
Graham
About the only electronic components I have with me at the moment are a home made prop board and an LC tank (Ferrite rod, coil, capacitor) ripped out of a dead DCF77 radio controlled clock. So, will it be possible to tune this thing down to 77.5KHz and create a propeller time standard receiver ?
Sadly I have no means of building this at my current location.
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For me, the past is not over yet.
-Phil
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'Still some PropSTICK Kit bare PCBs left!
Magnetic actuator for a 2.4g IR controlled model aircraft.
Graham
One can spend a lifetime running 'hello world' routines and blinking lights, but that has never been what Parallax wanted to facillitate.
The message here is that with a few simple tools, anyone can do far more than what a text book or tutorial teaches you.
The Propeller really allows you to explore outside the box of conventional digital wisdom. And it certainly·is all about exploring new uncharted territories. Thanks.
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It's sunny and warm here. It is always sunny and warm here.... (unless a typhoon blows through).
Tropically, G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
Post Edited (Kramer) : 8/15/2008 10:38:05 AM GMT
Salvage an AM transistor radio that has a speaker or try opening up an AM/FM clock-radio and I bet you'll find a ferrite rod or bar transformer/coil in there. Problem is you don't know what the relative permeability of the ferrite material is. No problem, just wind a bunch of turns on the thing and measure the inductance. The relative permeability is found using the attached equation which I scraped from this good page on ferrite antennas:
www.c-maxgroup.com/tech/antenna.php#01d
Air wound (paper tube) coils still have their place. All materials are at-hand usually. A toilet paper roll or some-such plus scavenge some wire from a dead wall-wart power supply transformer or an audio transformer from a dead dial-up modem. Radio Shack sells assorted magnet wire, Catalog #: 278-1345. Or just use the nice thin wire on a salvaged ferrite antenna and wind it on a paper tube, now you don't need to measure the ferrite relative permeability.
A nice tool for calculating air-wound as well as toroidal inductors is miniRing Core-Calculator. Download it here, it is completely free:
www.dl5swb.de
The link below has some good info on the ferrite transformer/coils you find in radios and how to modify them:
www.hard-core-dx.com/nordicdx/antenna/loop/amloop.html
You can buy ferrite rods with windings on them at the link below. But there's no technical information. In-fact I found these rods in other places as well but again, no technical information. Perhaps a deep search will turn else something up.
www.scitoyscatalog.com
I couldn't find a ferrite rod antenna on the Radio Shack site.
Regards, David
-Parsko
ps- Great project for a young baseball fan that's into electronics (a combination we need more of in this world of grotesquely publicized Olympics!)
I've already started looking through my shop for parts...
Question: what would it take to adjust to different frequencies?
Say aircraft (IIUC, it's close to AM) or even better police frequency.
Wouldn't this just be a matter of code?
OBC
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"One thing I'd like to come up with is an easy-to-fabricate coil (or transformer) with your recommended values, made solely from hardware store and/or Radio Shack materials."
See the·"Edit" to my original post.
If you are using a different value inductor, then use this ... http://www.deephaven.co.uk/lc.html·... to determine what parallel capacitor to use to approximate 1100kHz.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Also, you apparently have an inductance meter at your disposal. I suspect such an item is rare among most Propeller users — myself included. But this is something I'll bet could easily be fabricated using a Propeller and a few passive components. 'Any ideas along these lines?
-Phil
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'Still some PropSTICK Kit bare PCBs left!
Post Edited (Phil Pilgrim (PhiPi)) : 8/15/2008 8:29:54 PM GMT
Nice work and a very smart idea. Thank you for sharing with the community.
I am feeling something like a Propeller based DC77 receiver behind the lines [noparse]:)[/noparse] [noparse]:)[/noparse]
Regards,
Attila
-Phil
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'Still some PropSTICK Kit bare PCBs left!
"...Also, you apparently have an inductance meter at your disposal. I suspect such an item is rare among most Propeller users — myself included..."
What I have in the way of an inductance meter are a few·precision value inductors that are less than 1% tolerance that I can apply against an unknown inductor value using a method similar to what is described below...
Determine an unknown inductor based on results from a known inductor:
"...But this is something I'll bet could easily be fabricated using a Propeller and a few passive components. 'Any ideas along these lines?..."
An attempt at this with the Propeller was the Bode plotter, but because it was not technically a "Bode Plot" and there was a bit of grief over the reference, the topic was buried.· Here is a link... http://forums.parallax.com/showthread.php?p=579380
A true "Bode Plot" would show the ratio between the input and the output in a logarithmic format... What I did·only shows the ratio between Vdd and the output after a voltage divider.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Not sure if any of these has any audio modulation that you might actually hear. Just a pulse in the carrier level every second.
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For me, the past is not over yet.
-Phil
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'Still some PropSTICK Kit bare PCBs left!