jjwwjj@mixcom.COM (Robotic Systems) (03/27/91)
I don't know if my last message got out properly, so I am asking again: Does anyone have suggestions for a cheap, easy to build (ie. 10 chips or less) wireless modem? I need atleast 300 bps and a 50 meter range. I saw some talk here a week or so ago about a chipset from TI for FM communications. Could the poster please comment? Thanks in advance.
jeff@markets.amix.com (Jeff Crilly N6ZFX) (03/29/91)
In article <413@mixcom.COM> jjwwjj@mixcom.COM (Robotic Systems) writes: >I don't know if my last message got out properly, so I am asking again: > >Does anyone have suggestions for a cheap, easy to build (ie. 10 chips or less) >wireless modem? I need atleast 300 bps and a 50 meter range. > Cheap approach: find a low cost used 300 baud accoustic coupler or maybe a commodore modem (though the latter is a parallel bus). Hook this guy to the FM stereo transmitter described in other articles. Also hook up a FM receiver to it. Do the same at the other location. Use one channel of the stereo FM transmitter/receiver for each direction; or just use a seperate frequency for each direction. Make sure you also use protocol on the data. No doubt its not going to be error free. Let us know if it works. Jeff Crilly (N6ZFX) AMIX Corporation 2345 Yale Street Palo Alto, CA 94306 jeff@markets.amix.com, {uunet,sun}!markets!jeff, N6ZFX@N6IIU.#NOCAL.CA.USA
lairdkb@mentor.cc.purdue.edu (Kyler Laird) (03/29/91)
Electronics 1 2 3 sells a nifty RF trans/recv pair that can transfer 12 bits (8 ID code, 4 data). They use an encoder/decoder paird that they also sell. These units have a serial DATA IN/OUT line and demultiplexed address and data in/out lines. I _think_ that you could take the encoder and decoder out of the circuit and use the data lines for your own use. The schematic for the encoder and decoder shows an oscillator on each, but I can't find a speed rating. I doubt that 300bps would be a problem. Both units are board level and small (~1.5" x 4" - recv, 1.5" x 2" - trans ???). TX-88 RF Transmitter - uses a 'standard' 12V transmitter battery RE-01 RF Receiver - accepts one of 4096 (12 bits) codes RE-99 RF Receiver - accepts one of 256 (8 bits) codes, returns 4 bits data Since you would be bypassing the decoder section, the receivers are essentially identical. It's a shame that there isn't one that just returns all 12 bits for you to play with. Manufacturer: Ming Engineering & Products, Inc. 977 S. Meridian Ave. Alhambra, CA 91803 Voice: (818) 570-0058 FAX: (818) 576-8748 Dealer: Electronics 1 2 3 (division of Ming E&P, Inc) 977 S. Meridian Ave. Alhambra, CA 91803 Order: (800) 669-4406 Voice: (818) 261-4065 FAX: (818) 576-8748 Prices: transmitter $ 9.95 receiver $19.95 pair $29.95 These things look handy! I'm planning on getting at least one pair. They look like they'd be good for all sorts of digital communication. I'm interested in anyone's experience with them. Good luck! --kyler
fpm@gaak.lcs.mit.edu (Fred Mikkelsen) (04/01/91)
Kyler Laird writes:
Electronics 1 2 3 sells a nifty RF trans/recv pair that can transfer 12 bits
(8 ID code, 4 data). They use an encoder/decoder pair that they also sell.
These units have a serial DATA IN/OUT line and demultiplexed address and data
in/out lines.
TX-88 RF Transmitter - uses a 'standard' 12V transmitter battery
RE-01 RF Receiver - accepts one of 4096 (12 bits) codes
RE-99 RF Receiver -accepts one of 256 (8 bits) codes, returns 4 bits data
Since you would be bypassing the decoder section, the receivers are essentially
identical. It's a shame that there isn't one that just returns all 12 bits for
you to play with.
Manufacturer: Ming Engineering & Products, Inc.
977 S. Meridian Ave.
Alhambra, CA 91803
Voice: (818) 570-0058
FAX: (818) 576-8748
Dealer: Electronics 1 2 3 (division of Ming E&P, Inc)
977 S. Meridian Ave.
Alhambra, CA 91803
Order: (800) 669-4406
Voice: (818) 261-4065
FAX: (818) 576-8748
Prices: transmitter $ 9.95
receiver $19.95
pair $29.95
These things look handy! I'm planning on getting at least one pair. They
look like they'd be good for all sorts of digital communication. I'm
interested in anyone's experience with them.
Good luck!
--kyler
All Kyler's information is correct, except that there isn't a serial data
in or out capability. I ordered 3 each receivers and xmitters, they arrived
promptly, and they perform as advertised, BUT:
The documentation is ABOMINABLE. It's incomplete and partly (and obviously)
wrong. I called Ming up ready to flame someone to a crisp, but they explained
how to use the units and were duly apologetic about the docs; I relented. If
you have to call them, ask for John--he knows the product really well.
Key points:
I don't know the range. At least 50 feet through wood-frame structures,
anyway.
The transmitter will operate well on a 9volt transistor battery and draws
about 25 ma. The receiver takes 5volts.
I don't think Ming's encoder/decoder chips are very useful--what we're more
likely to want is digital data in and out. Fortunately this is easy to arrange
with just a TTL signal (driving an NPN base via 47Kohm) at the transmit end,
and TTL-compatible out. I've tried this with an oscillator driving the
transmitter and got over 9KHz before losing the signal, so my guess is the
baud rate could be 4.8K with reasonable hope of success. Transmission is
done simply by gating a high-frequency oscillator on and off.
The receiver is not happy with either "dead air" or a continuously transmitted
signal. A transmission every 0.25 seconds prevents problems.
The units operate on 300MHz. They claim to be kosher with the FCC "but this
has not been verified". What else is 300M used for, anyway?
The transmitting antenna is just a loop on the PC board about 3/4" by 1/2".
I'm impressed! Receiver antenna is 3 feet of wire.
John Purbrick
fpm@gaak.lcs.mit.edunagle@well.sf.ca.us (John Nagle) (04/03/91)
I think you've got a garage door opener. John Nagle