I need to create a RF circuit that will transmit a small amount of data, but it is time sensitive. I have been reading the tutorials and many other references…(maybe reading too much making my head hurt!) Here is how I understand it and please correct me if my reasoning is wrong.
If I use 300/400 MHz then to pass FCC, the transmitter has to shut down automatically. If this is the case then I have to take the load up time into consideration. So I think 900 MHz might be better.
I want a transmission range of around 300’ and reliable connection. I have been looking at a few different transmitters, Linx txm 916 ES, or RF Solutions ALPHA-TX915S. Any words on these or other suggestions?
What I want is I will have a few transmitters that when triggered will transmit a 2 “Word” message to the receiver. The first word will be an ID number to identify the transmitter that is sending the message and the second word will be a number to identify the type of action that the transmitter took. These transmissions are sporadic. The receiving end will need to pass these words on to a computer via a USB connection. In reading, it looks like I will need a micro-controller with USART on the transmitter circuit and a microcontroller with USART and USB on the receiver circuit. Does that sound correct.
Does this sound right? Any suggestions for the Micro Controller and Transmitter/Receiver?
I want to buy the parts and start experimenting but I want to start in the right direction.
400MHz… FCC says you can’t transmit very often - like minutes. Not enforced, but the intent is to share the frequency with others nearby.
902-928MHz in No. America - less stringent by far than the above.
Most inexpensive and easiest, for a newbie, is hardware and software you can just use.
Such as XBee which you can configure (not write code) to send sensed bits or Analog to digital converted data to a mating XBee (SERIES 1, not SERIES 2). One end can use USB. Perhaps you don’t need to write any code.
Or JeeLabs RFM12 on a board with an AVR micro - with Arduino code ready to use- if you’re proficient in that.
You don’t say what the 2 words might be; like 2 bytes? Created how? Data source?
If it’s simple enough to acquire the data to be transmitted, you might be able to use something simpler than the above.
Maybe word is the wrong term…I need to transmit 2 pieces of data. One is a number to identify which transmitter is sending the data. The other could be a number to indicate the status of the transmittter (only a few options are needed). The 2 pieces of data are created from the microprocessor in the transmitter circuit. The first piece would be hard coded and the second piece is generated based on a signal the microprocessor receives. The Xbee is not cheap! The JeeLabs is a little more reasonable. I would like to have all the circuits on one board due to space restrictions. I will research the Jbee… Any thoughts on the Linx txm 916 ES, or RF Solutions ALPHA-TX915S?
In low power low speed Wireless, cheap hardware == lots of your skills and labor to do in software what must be done, and isn’t done, in hardware.
If you lack the experience, skill, knowledge to do the software, or if you’d rather not spend weeks poring of all this, then get something like the XBee where it’s a “modem” to you.
Linx - rarely used in student/hobby world - so your ability to benefit from others’ projects is nill. With this kind of chip, you have to do the antenna design. At $13+, it is just a bit cheaper than a $21 XBee (shop around).
RF Solutions - also rarely used in student/hobby world.
I’ve developed some projects over the last 15 years using Linx products. I totally agree. Unless you want to spend money on their evaluation kit, which I refuse too, you’ll be responsible for ALL your software, which can get very time consuming and complex, esp. for a beginner. Laying out a board and setting up the hardware is not the problem. If your going much past a garage door opener project as with most products now-a-days these products often are software driven. Some of the Linx products you can use at a very simple level without software, such as a garage door opener. But, there’s no way to take full advantage of their products, even a basic controller network, without programing. Both at high level langurage for the PC and lower level programing for the on-board micro-controller. And don’t expect any support from Linx, other then the data sheets. Even though I’ve been doing this stuff for awhile, and I’m no expert, I’m still not up to snuff on it. So, ya for a beginner, go a different route.
I picked the Linx MS SERIES out of all silicon…at the time. I have a rectangular home lot of about an acre with a sprinkler system I installed myself. I didn’t want to use a cable(s), except the power, for all the valves, esp. the ones near the end of the lot. I needed something with a reliable, decent wireless range. At the time (15 years or so ago) Linx was the only one on the block with that range and had expandability capabilities. No network, just straight controlling. But in recent years a bunch of new comers have came on the scene, networking is the “in” thing, and choices have mounted. Though, I still think their product has better range then the rest, esp. XBEE. Of course your application and experience should help dictate your choice.
My first demo. project started with a garage door opener which has been running reliable for many years. Yea, it’s overkill, but for demo purposes I can get nearly a half mile range. With 8 status lines you can add many more things to turn on and off. The new stuff is of course data capable. Also backwards compatible with the older stuff.
Their MS series has since grown to include a full bi-directional (transceiver) capability and I have worked to take advantage of that added capability. So I have a little experience with this particular product but I’ve grown with it over the years in experience on the newer capabilities they offer.
Don’t expect any support from Linx other then the data sheets. But with added capability obviously have come complexity and the additional need for programming. For a beginner I’d pick something that doesn’t require so much time gaining experience in both hardware and programming.
While the IC’s are readily available, I haven’t seen any bare PC boards available except what Linx makes and I think they are mostly complete units. I made my own. With stacked, double sided, boards I can make a remote (slave), except the control relays, in LESS then two square inches without really trying to optimize board real estate.
I also made a board with a USB converter on it so I could use a PC as a master controller using a Visual Basic user interface. Don’t use the Linx USB to serial converter IC. There are several better options out there. It’s still a work in progress. I still like the product but its not for the “faint at heart”.
I still think it’s a good system, just not one for the “weak at heart”.
Two IC’s such as the Linx MT series transcoder and the Linx TRM-418-LT transceiver plus a micro controller would work. I know I’m a little out of cognatio with the Parallax crowd but I use the micro I’m familiar with programming, the Motorola MC9S08QG8 or MC9S08QG4. Not to get off the subject but yea, I’m also a Linux OS guy.
This Linx two IC solution offers what your describing, two bytes, one assigned as a ID byte and one as a custom data bit. The transcoder takes care of all the encoding and decoding via a standard, uni-directional, asynchronous serial port. Any decent micro-controller offers that capability.
Your probably a lot shaper then I am but there’s a steep learning curve to get to that stage of maybe getting them to network. Buying the evaluation kit would speed that up considerable if you want to spend the big bucks.
One caveat, I’m not familiar with all the other products on the market so familiarize yourself with all the manufactures/products first.