Forums

WLAN card to generate pulsed RF?

Started by Joerg October 26, 2006
Hello Nico,

>> >>>>AFAIR I got over 50bps out of it but the flyback transformer in the >>>>monitor was screaming so bad that I stopped. Don't know what an >>>>LCD could do though. >>> >>> >>>Probably less. You can forget blinking the cold cathode lamp - the >>>invertor is probably too slow to drive in all cases. I guess assuming > > > The inverter can be driven on/off at several 10s of Hz, but it takes > several 10s of ms for the driver to reach full output. >
Yes, but I'd rather not flick the inverter unless I know exactly how it is designed. PWM circuits often exhibit some bizarre pathologies and some lamps might not like this mode either.
> >>>a 30 Hz refresh rate will be conservative enough, and with some more >>>conservativism you go down to the 10 bpS, which I am sure can >>>be doubled if you tweak all of the above and some more :-), but >>>that will be about all, I guess. >>> >> >>There is no easy access to the CCFL generator. But many LCD can probably >>be cycled at 30 Hz because that is the frame repetition rate of US >>television. > > > That depends entirely on the speed of the LCD screen. Latency of TFT > lies somewhere between 4 to 10ms. The latency number specified for TFT > screens is the sum of the time required to go from black to white and > from white to black. A screen rated for 8ms may have a white->black > time of 2ms and a black->white time of 6ms. > > With OpenGL it is possible to update the screen buffer on vertical > blanks. Since almost every TFT screen is driven at 50Hz, you could > make the display flash completely at a rate of 25Hz (40ms period). A > good Windows programmer should be able to program something like this > in a few days. >
Thanks, Nico. That is excellent information. It wouldn't be necessary to swing between the extremes, a good photo receiver circuit could work with 25% modulation or even less. -- Regards, Joerg http://www.analogconsultants.com
Hello Robert,


[ ... ]

> >>>What is that you have that continues to require the DOS box that can't >>>be replaced with Win32 command line code? >> >>Any program that is supplied as binary (.com or .exe), since the >>original company might not exist anymore. > > Certainly that's the usual case (or something homegrown and not moved > to 32 bit). That's usually the case for one or two point > installations, but the poster I was responding to claimed this made > Win64 unusable for their entire office and lab. > > So the question remains, why can't they move to a Win32 app? In many > cases the reason is either inertia (haven't upgrade my copy of > SuperWhatsit since 1994) or misconception (Command Prompt = DOS Box), > in which case it's not a real limitation. >
There are some SuperWhatsits that simply cannot be upgraded. Mostly this happens when a university group that produced excellent work and useful routines has disbanded. Either because they moved on to something new or because the professor retired. Academia isn't exactly known to maintain older things like we do in industry. Example: "FilterDesign" from Prof.Mildenberger, Wiesbaden, Germany. He retired and now they even took down his web page. It's a great and rather indispensable program when you have to design wave digital filters. The PC switches to full screen DOS to use it. Besides routines from TI there isn't much else. Those routines are also hardcore DOS, including one that was released this September. Bottomline is that if MS drops DOS this business will not upgrade anymore for a long time and then possibly migrate to another OS. Why should we upgrade if that reduces productivity? -- Regards, Joerg http://www.analogconsultants.com
Hello Vasile,

> >>The scenario I imagine is this: >> >>a. The target device is equipped with a simple and not very sensitive >>receiver and AM detector for 2.45GHz ISM (WLAN range). This runs into a >>comparator port of the uC. Much simpler than Bluetooth and all that, >>plus lots of laptops don't have Bluetooth. > > This is perfect possible with any transciever having an analog RSSI > output (like MAX2820 to MAX2829 or a digital RSSI output like Chipcon > devices) *IF* woud be used in a clean RF environement (near and on the > 2.41-2.48Ghz ISM band there are a lot of licensed and unlicensed > activities: WIBRO, WIMAX, WIFI, WIBREE, Bluethooth, Zigbee, etc) >
RSSI is one option. Sometimes the chip that includes it costs too much. Then I use transistors. But at 2.45GHz a chip might be the better deal. Still single source, usually, and that is always detrimental from a business perspective.
> >>b. The user receives one executable file containing the new firmware, >>code to initialize the WLAN port and code to run that port in a simple >>(but legal) AM on/off mode. This executable would now be started. > > Again, only IF the executable will be received clean and the CRC will > be OK. > Much doubt will be like this on long distance. >
It's not long distance. The target device would be right next to the laptop.
> > >>c. The user is instructed to press a magic button combination which sets >>the target device into re-flash mode, upon which it waits for a data >>stream from the WLAN card. > > Ohh, software... without a good hardware means zero. >
That's why we only design the good stuff :-)
> > >>d. The user must place the target device within a couple of feet of the >>WLAN equipped laptop until a LED flashes, indicating that it has >>detected the presence of a sufficiently strong pulsed carrier somewhere >>around 2.45GHz. > > > Like someone said, a microwave owen or a Zigbee transmitter very close > to your receiver :) >
It's in the field. Not much around it, plus the field strength two feet from the laptop will swamp almost any other source. The user is, of course, not supposed to do this next to a microwave while heating a bag of Redenbacher's popcorn in there :-)
> >>e. A serial on/off data stream is constantly pouring out of the WLAN >>port of the PC. A bootloader in the target device looks for a passcode >>and when it finds that it loads the data stream that follows. >> >>f. The target device stops at an end-of-file token, does sufficient >>integrity checking on what it has received and then leaves re-flash >>mode. It's now ready to use with the new firmware. >> > > So, why bootloading over the WIFI ? >
Because you will neither need any cables nor any accessory to the laptop. Wifi is mostly already built in. -- Regards, Joerg http://www.analogconsultants.com
Hello Paul,

>> >>>The scenario I imagine is this: >>> >>>a. The target device is equipped with a simple and not very sensitive >>>receiver and AM detector for 2.45GHz ISM (WLAN range). This runs into a >>>comparator port of the uC. Much simpler than Bluetooth and all that, >>>plus lots of laptops don't have Bluetooth. >> >> >> This is perfect possible with any transciever having an analog RSSI >>output (like MAX2820 to MAX2829 or a digital RSSI output like Chipcon >>devices) *IF* woud be used in a clean RF environement (near and on the >>2.41-2.48Ghz ISM band there are a lot of licensed and unlicensed >>activities: WIBRO, WIMAX, WIFI, WIBREE, Bluethooth, Zigbee, etc) > > > Yes indeed. > > Any application running in the license exempt bands that also are ISM > bands, such as 13.5 Mhz, 27 MHz, 2.45 MHz (and 900 MHz in the US) > should be designed to be idiot proof. Anything can happen on these > bands. >
Absolutely. There needs to be a simple "Re-flash successful" and "Re-flash failed" signal, nothing else. Plus the option to just leave the target there for a minute until the "Re-flash successful" light has finally come on.
> When using applications running on a licensed frequency, you can > always request the licensing authority to handle the interference > problems. >
Good luck with that one. Tried it a few times. You are usually dealing with huge bureaucracies there. "Speed" can take on a very different meaning. -- Regards, Joerg http://www.analogconsultants.com
"Didi" <dp@tgi-sci.com> wrote in message 
news:1161902599.701518.7240@k70g2000cwa.googlegroups.com...
> Hi Joerg, > >> The advantage is that it doesn't need a hole, just a translucent section >> in the enclosure. > > I agree, this is a significant advantage. Probably the way to go if you > have > to be waterproof - you will still be able to make 10 bpS easily, which > at your > 1 - 2 K is still adequate (vs. the 300 bpS of Kansas City). > The main disadvantage I see is the necessity to write some modulation > software for Windows (yuck).
Could always use an ipod screen. Make a "music video" that has the correct modulation. Alex
On 2006-10-26, Joerg <notthisjoergsch@removethispacbell.net> wrote:

> That would require filtering but could be done. At least it's better > than using audio because that would be really annoying to others.
only if it's audible, I'm sure the speakers in most laptops will go to 22KHz without much effort.... -- Bye. Jasen
On 2006-10-26, Joerg <notthisjoergsch@removethispacbell.net> wrote:
> Hello Nico, > >> >>>The only other option I could think of (and I have done that before) is >>>to provide a photodiode and let the LCD screen flash. However, that is >>>really slow and can annoy others who have to work close to that laptop. >> >> >> Why not use the audio output of the laptop? Every laptop has one and >> it is very easy to program. If you get really nifty, you can >> distribute your firmware as an mp3 file. >> >> Still, I think USB really is the sensible way to go for these sort of >> things. USB to serial adapter chips are commonly available and small >> (like the CP2101). Cabling is not an issue if you use standard >> (miniature) USB sockets. Drivers can be made available from your >> website. >> > > Either one needs cables. People forget to take them along, they can be > damaged, connectors become dirty, it could be raining or snowing etc. > The audio port on laptops is a 3.5mm audio jack. Those are IMHO rather > unreliable. USB is bulky and expensive.
audio needs a microphone built into the device and a demodulator, no cabling. Bye. Jasen
On 2006-10-26, Joerg <notthisjoergsch@removethispacbell.net> wrote:
> Hello Nico, > > Not really since the field strength two feet from a laptop will be > vastly higher than even a router in the next room. Unless it happens to > be right behind the wall but then the user would know that or have to be > educated about stuff like that. For an AM protocol to work quite well > you wouldn't need much more than 6dB of SNR above other WLAN participants.
yeah! If the data was encoded in the lengths of the wifi bursts and the gaps between them were arbitrary (which they neccesarily would be) it might be able to work.
> > >> ... If you re-program your WLAN adapter to >> output other patterns that usual, you'll be building a WLAN jammer. >> > > Definitely not. Even if legal it would be unethical. First, there are > about ten WLAN "channels" in most countries and you'd only block one. > Second, you don't even have to block that one channel. The card could > send really brief bursts and the duty cycle could be kept to a few > percent. Then you would be less of a burden to other users than a kid > that downloads the latest and greatest iTunes song or YouTube movie. > Whatever they find funny about those movies... > > Keep in mind that the typical uC in a small target device contains only > 1-2k of code. It doesn't take a whole lot of channel capacity to scoot > that over. You could be done in under one second if needed. That's > hardly a jammer ;-) >
-- Bye. Jasen
On 2006-10-27, Joerg <notthisjoergsch@removethispacbell.net> wrote:
> Hello James, > >> >>>Bluetooth is indeed too complicated. Speed is not an issue as it can be >>>even slower than 2400bd. Much slower if needed. But simplicity is >> >> [...] >> >>>Irda would have been nice but this seems to not really have caught on. >>>None of the laptops I have checked had it. And even there it would >> >> [...] >> >> I think you probably could send at least a few dozen bits per second >> via the keyboard num-lock/caps-lock/scroll-lock LED's. I don't know >> what the API is like in Windows; under Linux, see man setleds >> and/or source of same. setleds works on virtual term's, not xterms. >> For xterms, see code at >> http://www.lugod.org/mailinglists/archives/vox-tech/2005-07/msg00097.html >> > > Now that's an idea. Except that on some laptops (like the Dell here in > the office) these LEDs are rather dim.
or lcds ... -- Bye. Jasen
Hello Jasen,

> >>That would require filtering but could be done. At least it's better >>than using audio because that would be really annoying to others. > > only if it's audible, I'm sure the speakers in most laptops will go to > 22KHz without much effort.... >
But I am not sure the electronics will. AFAIK 22kHz would be really close to the Nyquist limit of lower end sound chips. Also, 22kHz could drive animals such as dogs nuts. We have a little beeper (called ultrasound but it's really only around 25kHz). While our rottie could care less because he is quite noise tolerant a terrier that was visiting almost fell off the stairs when it sounded. -- Regards, Joerg http://www.analogconsultants.com