Cheap, slow, through-wall RF? - Page 1
Forum section: electronics / projects

author: bronson
author_rank: Regular Contributor
timestamp: April 25, 2014, 11:20:18 pm
content: Or, does anyone know what 915 MHz technique the $25.00 LaCrosse weather station uses? Its range, data rate, and power usage are perfect for my needs. To figure out which RF chipset they use, I bought one and opened it up... and saw two COB blobs, nothing else. Drat.Why: I want to scatter some small sensors (temp, pir, beam break) around the house and shop. Every few minutes or hours (any time something interesting happens) they will report their reading to to home base. Each burst of traffic is 4 to 8 bytes: 2 byte ID, 2+ byte reading. Figure I'd use an ATTiny in each sensor, maybe a Raspberry Pi as the base station, pretty much anything would work.I'm not seeing a good way to implement the RF. BTLE is close but has range issues. Most sub-1-GHz chipsets I've found are relatively expensive ($8+) and have way too much bandwidth. I want less!TI's CC100 seems closest but still a little expensive for what I want. There's gotta be something like it, but less integrated and cheaper?Thanks for any hints.

author: calexanian
author_rank: Super Contributor
timestamp: April 26, 2014, 12:42:42 am
content: Most of them use Micrel. TI now has some of them.. here are many 915 rf module companies making them on the cheap. I have many 433 TX/RX pairs from a former product. We bought them in 1K qty for like 2.15 each for the transmitter (TX is always cheaper) and 3.75 for the receiver. We changed the design to Linx technologies. They are a more expensive better product, but essentially the same thing. I think digikey carries them. As for the cheaper ones, you can find them online for just above nothing. Don't expect to pass FCC with them right out of the box though. For projects they work fine.

author: bronson
author_rank: Regular Contributor
timestamp: April 26, 2014, 08:22:17 am
content: Thanks calexanian. The Micrels look interesting but still more expensive than I'd think (2x$2.50 RF chips don't leave a lot of BOM room for a $25.00 product). Linx looks really sweet but, yeah, pretty luxury.I just ran across the TI CC430... If it lets me ditch the ATTiny (and it looks like it can), then it actually fits pretty well. Now I need to wade through all this crazy TI documentation to figure out which dev kit to order...

author: calexanian
author_rank: Super Contributor
timestamp: April 26, 2014, 05:05:46 pm
content: Many of the cheap manufactures use Laipac Technologies. They suck, but they are cheap! In production volume they are dirt cheap.

author: lgbeno
author_rank: Frequent Contributor
timestamp: April 26, 2014, 05:21:24 pm
content: I'm on the 43oh forum too where this sort of topic is discussed a lot. Cc430 is a cool part and would accomplish what you need. Like all things, in low volume you'll end up paying $3-$6. People there always talk about panstamp.Another option is Nordic nRF24 there are dirt cheap modules out there. It's 2.4GHz but could would through to house I think. There are great libraries for Arduino and energia too.Another option is hopeRF that's probably the closest that you will get to LaCrosse.Also if you search for gnu radio projects receiving and decoding LaCrosse packets with an RTL SDR there are projects like that as well.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 26, 2014, 05:24:03 pm
content: I recently completed a project (wireless tally lights for a multi-camera TV studio) and used Moteino modules from LowPower Labs. They are very tiny boards with the equivalent of an Arduino Uno microcontroller along with HopeRF RFM69 transceivers in 434Mhz (universal), 868Mhz (EU), 915Mhz (US, Australia, etc.) bands. They are US$20 each, but they provide the entire controller/interface/communication all in an easy to use integrated package. I'm buying more of them. Great stuff, IMHO.http://lowpowerlab.com/moteino/

author: calexanian
author_rank: Super Contributor
timestamp: April 26, 2014, 06:25:29 pm
content: Laipac.. They are cheap.. that's about it.http://www.laipac.com/gps_rf_components.htmThere was also another company run by a guy named Frank Lin. He was from Hong Kong, or Taiwan and they did assembly in mainland. He makes all of the key fob designs for the car manufacturers.. I cant find his card unfortunately and his company is impossible to find without it. They actually intentionally hide a little bit. They have the TI-Micrel hookup. Also he is plugged into TSMC somehow.

author: Gribo
author_rank: Frequent Contributor
timestamp: April 27, 2014, 06:30:07 pm
content: The CC1101 is not really a narrow band transceiver (~50KHz minimum RX bandwidth), The CC1120 has better performance at low data rates, also it has a higher price.You should also consider Nordic semi and Energy micro (Silicon labs now) both have a line of transceivers for such applications.

author: bronson
author_rank: Regular Contributor
timestamp: April 28, 2014, 06:20:28 am
content: Thanks to everyone for the suggestions. I'll be ordering the CC430s tomorrow in the hope that I can have a 1-chip board, no module needed. (looks like Nordic might offer that too)If that doesn't go well, I'm coming back here to figure out plan B.

author: calexanian
author_rank: Super Contributor
timestamp: April 28, 2014, 07:03:02 pm
content: Yeah, the TI chips are pretty Smec. What kind of quantity are you looking at? If you just need a few modules and cal live in a different ISM band i can send you a few of what I have laying around to play with..

author: lewis
author_rank: Frequent Contributor
timestamp: April 28, 2014, 07:26:00 pm
content: Take a look at the ALPHA-TRX-433 from RF solutions. Also sold as the RFM12B from Hope RF. They're 433MHz, which might work better through walls than 915MHz, but the FCC limits you on how much/often you can transmit at 433. You can get them in 315, 433, 868 and 915MHz too. Real easy to use, FM, ~100m LOS with even a shitty antenna, and they're cheap!Page 27 of this is very useful for global ISM bands:http://www.ti.com/lit/sg/slya020a/slya020a.pdfTransmitters and receivers:http://www.rfsolutions.co.uk/acatalog/Alpha_Transmitter___Receiver_Modules.htmlTransceivers:http://www.rfsolutions.co.uk/acatalog/Alpha_Transceiver_Modules.htmlRFM12B:https://www.google.co.uk/search?q=rfm12b&oq=rfm12b&aqs=chrome..69i57j0l5.1754j0j7&sourceid=chrome&es_sm=122&ie=UTF-8