Newsgroups: sci.electronics Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!think.com!mintaka!gaak!fpm From: fpm@gaak.lcs.mit.edu (Fred Mikkelsen) Subject: Re: Wireless Modem (RF data transfer units) -- I got one! Message-ID: <1991Apr1.082241.4084@mintaka.lcs.mit.edu> Summary: Ming Electronics products Keywords: wireless modem fm radio data Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius) Organization: MIT Laboratory for Computer Science References: <413@mixcom.COM> <1991Mar29.070109.11684@markets.amix.com> <9029@mentor.cc.purdue.edu> Distribution: usa Date: Mon, 1 Apr 91 08:22:41 GMT Lines: 81 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.edu