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Remote Telemetry With Your PC?
hyacinthus asks: "For some projects I'm working on, I'd like a system for acquiring data (as from the output of an instrumentation amplifier) from a module that would be separate from a PC, a maximum distance of perhaps several hundred feet at most, and the use of cable or wire is not an option. My bandwidth requirements are very small--perhaps a hundred 12-bit samples per second would do it. I would like the data acquisition module to be as small as possible. And I'd like the possibility of acquiring data from more than one module, rather like a multiple-channel data acquisition system." Are there any radio-based PC products that can be adapted to suit this sort of task?
"Commercial data acquisition products for personal computers all tend to be rather spendy, and none that I've seen make any provision for wireless telemetry. I've been considering designing and building something, probably using one of the commercial available USB development kits (see, for example, ActiveWire's USB board). But I'm no electrical engineer (a few digital design classes and some self-teaching from Horowitz and Hill, and that's it), so I'd like to ask if there's anything out there which does what I want."
There's a bunch of solutions out there if you want to be a little crafty, and most of it is just limited by how much you want to spend and how reliable you need the data transfer to be (as you can guess.. the two are linked :).
A couple people have suggested a laser link. I built a small one for experimenting using a UART and some of the schematics from the book Lasers, -Ray Guns & Light Cannons ISBN: 0-07-045035-8. (Someone better buy it because I had to dig through two years of crap to find it! :) I got the lasers from some surplus place cheap. It worked well at 2400 baud or something like that, I was trying to build a circuit to act as a wireless point-to-point link to get high speed internet just slightly off campus (e.g. through my lab window to a buddy across the street :). It worked well, although I ran out of time to finish it. Think I was planning on selling them to build cheap point-to-point links at the time, or something. Hard to aim, though. Anyhow.
Another way is through wireless modules like the folks at Lynx Technologies or Parallax Inc. The parallax ones are of better quality right out of the box, and they'll sell to individuals, the former was nasty to me when I wanted to order some samples.
YET another way is through using Ham Radio and packet. You can get an all - in - one unit from Kenwood called the TH-D7A that is a small handheld with a 9600 baud TNC built into it. It's truely plug-and-play. Extremely expensive at $550cdn a pop, I know, I have one. You also need to be liscened to operate at these frequencies, and most/all places won't sell you one without your callsign or liscence. These work VERY well.
That said, one of those options will be the best for you. IR is out as it doesn't work worth a damn in direct sunlight, even laser detectors have a bit of a problem with sun. Sun is a great source of optical noise :). If I was needing something mission critical and a long distance, your best choice is the kenwood/packet option, or maybe the parallax modules. They hook right up to a serial port.
Alternately, you could just get a cheap 486 notebook and get a 802.11 card, and wire the whole thing to a big-ass car battery (find one that takes 12V, and make sure to put a fuse on it!). That might be cheaper in the long run, and will provide a lot of bandwidth.
Hope that helps.
..don't panic
This is all well and good for a hobbyist. In fact, there's quite a bit of Linux software for doing instrumentation this way.
If your application is professional or you want dead accuracy, please do not do this. How calibrated is that input amp? How about noise? What if you have to manually calibrate?
If you must use a laptop, NI sells some cool PCMCIA cards for this sort of use. Expect to pay for it, though.
That said, I'll have to mention that any x86 is probably overkill. I'd likely use a PIC and some choice Analog Devices chips. They are dirt cheap, and would be much easier to make immune to noise. You can control the whole design, which is a good thing. The less bloat, the less chance of interference.
For extremely critical apps, you'd probably end up doing some expensive testing, but you'd end up doing that for anything off-the-shelf anyway.
As for the data transport, if the speed isn't critical, you could do this. Just pick a frequency that you can use freely and make sure that nothing else around will interfere with the signal.
There are also a lot of other ways to do it. Radio is cheap to do, and more fault-tolerant than IR.
Look around, you might find something else.
http://www.ramseyelectronics.com
They have micro telemetry/control transmitters and receivers good for a few hundred feet (maybe a bit more). They're probably not the only source for these particular units, but since I just saw them in the new catalog, I thought I'd mention it.
Part numbers RXD-433, TXE-433.
...is a large, spinning mirror, and a tracking device...
...and we could vaporize a human target from space!
Yeah, *sure*, that's why you want it. We believe you...
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pb Reply or e-mail; don't vaguely moderate.
I just have to ask: why does the PC have to be so far away? Are these experiments dealing with strong electromagnetic phenomenon? If so, then I'd understand, but otherwise, several hundred feet would seem paranoid.
"Ancillary does not mean you get to rule the world." --U.S. Circuit Judge Harry Edwards, speaking to the FCC's lawyer
Unfortunately they are a little expensive at about $1200 per radio.
I've used a Cat-5 cable as a serial cable for distances over 800 feet. This was for 9600BPS, connecting to a router. It worked great, and I never had any problems. I think you really only need 3 wires for serial (that's all I had connected), so you could get a few serial lines in one CAT5 cable. That's the cheapest/easiest route I can think of; but I'm sure that there are wireless solutions. HAM guys will tell you about the 2400BAUD wireless packet radio stuff; this would work I'm sure, but it's cost is a little higher than just a cat5 cable!
Cheers!
-Eric
If InfraRed does not have the range, and line of site is possible, you could look into making a simple laser diode/receiver that hooks into the serial port for data transmission.
Anyone have any schematics? An old Popular Electronics hacked up two laser pointers to make a simple wireless transmitter/receiver for voice (the microphone modulated the amplifier feeding the laser I think). Anyone up to modifying it for 9600 baud data?
Dan
dan_linder.at.yahoo.com@somewhere.else
(Remove the "@somewhere.else" and replace ".at." with "@" to e-mail me.)
I'm not too sure that I understand exactly what you want, but I'll give this a shot. From what I gather, you have X number of instrumentation installations spread around a local site. You want to collect the data from all of them with one central unit, and then dump the data to a PC. I would do one of the following...
:)
:)
:)
1) Set up an RTU data recording device and attach it to each sensor collection point. Depending on the type of sensors you use (0-2.5V. 4-20 mA, RS-232 "smart sensors", etc...), you should be able to find a relatively inexpensive Datalogger/RTU that fits the bill. If it is to be located in a harsh environment (outdoors, cold, etc.), make sure you have a board and enclosure suitably rated for such conditions (you can find severe environment units from www.lakewood.com).
Next, get an RS-232 -> Ethernet device. ZWorld had a spiffy programmable one that can be found at http://www.zworld.com/emseries.html.
Finally, get an 802.11 wireless device and connect it to the ethernet output of the RS-232 -> Ethernet "modem".
The nice thing about this setup is that you don't need any crazy serial input boards or wireless RS-232 devices. Everything comes in through a nice packet switched TCP/IP network. This is a blessing for keeping the end user software simple and stable.
2) One other possible solution is to do all of the above, but with one change. Instead of the RS-232 -> Ethernet device and the 802.11 connections, simply attach a Mobitex, CDMA, or CDPD wireless device to the RTU's. Granted this has some more cost associated with the mothly fees, but most carriers have lower cost "data only" packages without all of the crappy consumer features that you have no need for. And again, this has the benefit of a packet switched connection. As well, if your sensors are REALLY far apart, this might be the most economical solution in the long run due to the extra cost of "repeaters" and such. Plus, most of these types of devices already have the capability to connect to RS-232 components without extra hardware. And, if you're lucky, you can get the whole package in a 99 dollar heavily subsidized digital phone from your favorite carrier
Just my humble opinion, from a humble man who has done these things before
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