Slashdot Mirror
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.
If you're into electronics at all you would be crazy not to be a regular Circuit Cellar magazine reader. They have the kinds of articles perfect for the hardware/software hacker. In issue #113 from December 1999 they had a feature article on a Poisson network.
Basically it's a one-way RF network where each sensor (doesn't really matter what kind) has a cheap RF transmitter and a uC. They're using a Poisson distribution to create pseudo-random transmission intervals for each sensor, so that the likehood of collisions is minimized, since there's no network master, only a receiver that aggregates all valid transmissions it receives. The nice thing is that the per-node cost can be extremely low, depending on what kind of sensor you have.
Email me if you want some more details or some help on getting your hands on the article.
"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."
Sounds like a few modifications to a cheap guitar wireless unit would do it. They even got some close-outs at Nady.
AdFuel
Instead of designing and building a complex digital telemetry system, why not use some old analog technology? Many early telemetry systems were analog. The sensors were connected to VCOs (voltage controlled oscillators), and the VCOs were mixed together and used to modulate a FM transmitter. This was a simple, cheap and reliable package. The data acquisition station had a FM receiver, its audio was fed to a bank of FM discriminators, one discriminator for each VCO. The outputs of the disciminators were connected to a stripchart and/or a set of ADCs for computer processing. This works great for systems with a small number of parameters that need to be collected. The output of the FM receiver can be recorded on an ordinary analog magnetic tape recorder for archival storage and analysis. For some sample frequency plans, this page has tables listing the standard frequencies used in IRIG (Inter-Range Instrumentation Group) FDM (frequency division multiplex) systems.
Mea navis aericumbens anguillis abundat
the only link i found of interest was a packet radio modem kit for ibm pc's.
see packet radio modem kit it's $59 for one end.
I know they have "ming kits" too, but they do not appear to be on the web page. geez, i wish someone in st. louis would learn php or something.
Treatment, not tyranny. End the drug war and free our American POWs.
See my user info for links.
you need to be a ham and have tx and rx to use packet i think...
Treatment, not tyranny. End the drug war and free our American POWs.
See my user info for links.
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.
niode stands for Network Input Output Device for Ethernet. Basily you have a 10baseT, 10base2, or 10base5 port on one side and a DIDO port on the other. You communicate to it via a standard ethernet network and UDP packets. In fact If you need wireless just add a wireless ethernet converter ($$$) and its wireless. Multiples no problem just have to give each unit its own IP address... Currently I have most of the basic functions done (ethernet config, ARP, PING, and basic UDP packet handling) just need to finish up the code that takes the data from the packets and does some thing usefull. About 3 more good days of work and it could be done but need to actual work on it... URL is http://members.home.net/wireb/niode/niode/index.ht ml best of all they will be cheap. I am expecing the part cost to be under $50 for everything when done. Yes I know the page is not up to date (will get to it some day too busy working on the project right now.)
If you want to go several hundred feet, transmit RS-232 with a laser pointer.
Notice that X10.Com, and other sources, have "wireless audio" devices. You can feed the output from a modem to an audio transmitter. You need a modem which will transmit even though it does not receive a carrier from the other end. If the modem also has a two-wire or four-wire "leased line" mode then it also is easier to interface -- if you have to emulate a phone circuit then you'll need a half-dozen more components. And you'll need a data rate fast enough for your data...
Connect a four-wire leased line modem to it and you have a two-way data link. (Many modems have "leased line" mode, but a four-wire has separate audio wires for send and receive -- you can convert a phone modem to four-wire by building a phone-to-audio converter, which might be as simple as plugging in a telephone and battery)
...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...
---
pb Reply or e-mail; don't vaguely moderate.
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.)
would use a UHF sender and reciever.
It doesn't require line of sight, so its not like Infra-red, and you could probably get disant bandwidth (9600 baud)
you could most likely get the parts from a disected UHF remote-control.
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
Feel free to contact me on ICQ 34034928 if necessary. My listed e-mail is a fake
"You should read my new book: Humility, and how I attained it with 343 Illustrated Pictures of the Author."
You can make pretty cool robots/remote sensors/positronic brains with BASIC stamps gotten from radio shack. You can write a little diddy that takes the sensor data and streams it to an I/O port. Modulating the data collected for tansmission can be done in lots of ways. You can modulate the data and then just transmit it. The PC on the other end demods the signals and captures the datastream. Plug the stamp's I/O pins into a little AM or FM transmitter. Don't bother about duplex communication unless you ABSOLUTELY need it. BASIC stamps have pretty limited memory which means interactive programs aren't going to be very easy to make if at all. I've never heard of any major protocol ported to a microcontroller. I suppose the best method would be to build a mini-RF modem and modulate the data on the controller then stream it to the transmitter.
I'm a loner Dottie, a Rebel.
I like this, but I would skip the phone/modem part (number one, the phone is going to cost a bit more than $20 - probably closer to $40). Instead, use a couple of walkie-talkies. Cheap kids toy kind - or more expensive (less interference) family radio kind.
You only need one transmitting, and the other receiving. Set up a tone generator on the trans part, supplying high/low/mark tones (three tones, to indicate start, data, stop bits). The receiver's speaker output could go into the computer's sound card. Record and analyse the waveform data to get your data stream.
Now you may be wondering "How the heck do you do multiple channels with this idea?"
The answer to that? Round-robin.
Say you have three sensors, each with a walkie-talkie attached (a fourth walkie-talkie is at the "base station" PC). Two walkie-talkies are in "listen" mode, one is transmitting. The "base station" walkie-talkie listens all the time, and records all the sound (via the sound card in the PC). When one sensor walkie-talkie finishes, the mark tone for the next sensor walkie-talkie in the round-robin is sounded, causing that walkie-talkie to switch into transmit mode, and the first to receive. These mark tones are unique frequencies for each walkie-talkie in the round-robin (so, you would need a tone generator and decoder for each walkie-talkie sensor system - use a 555 for the tone generator, and a 567 for the decoder).
A kludge? Yep.
One other possibility is to just have them all transmitting at once - the signals will overlap - and then doing some hard-core waveform analysis on everything (maybe you could put a carrier tone on each). Or, you might be able to retune a bunch of walkie-talkie pairs, then select each pair at the base station PC via the parallel port (and an analog switch IC), feeding each walkie-talkie output in fashion to the PC sound card input...
You would probably get the same kind of line-of-sight distance as the AC's solution, more with the family radios. Shouldn't cost more than $40 per sensor on the low end (plus some blood, sweat, and tears to wire everything up and code the software interface).
I support the EFF - do you?
Reason is the Path to God - Anon
Try National Instruments FieldPoint system. It's a rugged distributed I/O system with wireless, serial, ethernet and Fieldbus options.
:-)
Look at the Fieldpoint section on NI's site
Yeap, you guessed it, I work for National Instruments
Seriously though, there are some very interesting options with the NI gear.
You might try these cheap 300MHz Transmitters and Recievers (also available from Digikey.com for a higher price). You can read about EE476 students using them in a customized RC truck here.
thad
I love Mondays. On a Monday, anything is possible.
you could try these guys. i think they have something called "ming kits" that let you write parallel data in and rcv parallel data on the far side.
they have stores in denver, san diego, st. louis.
if you need details via phone or email i'd try to hit up the san diego store first, i think they have an old navy fart working there who knows the most about their radio kits.
a one-way link will probably set you back like $100 just for parts, but i'm guessing.
Treatment, not tyranny. End the drug war and free our American POWs.
See my user info for links.
Actually, and interesting thing....my friend MattH does a radio show online (an on the radio) and last year we did spots that included On-the-scene reporting (for instance...outside for the weather and such) we actually used FRS radios. We used a small, 2 channel mixer, and it worked really well. I would be outside with one radio, and he would be inside with the other. I would talk through the radio, from whatever location I was at (up to 2 miles away) and he would recieve it all on the computer and stream it using shoutcast and winamp. It was sorta interesting and could certainly work. It would also be fairly cheap...50 bucks for a coupla FRS radios (which almost everyone has nowadays) and 75 for a cheap mixer (or run it straight into your line-in jack).
The anti-salmon