Ok, but will it work? About the maximum I will ever need to transmit is about 10 feet, and receive from possibly 50-75 feet in open space with lots of people in it. In the case of the 50-75 feet, the transmitter there would be a separate device with an actual bullwhip antenna. Space constraints are not really as much of an issue for that as the hand-worn modules. If I can get 10-15 feet of reliable tx/rx between two of these modules using chip antennas, I will be happy. That being said, with such a low dBi, will there be a large risk of dead spots, aka can’t link up the modules if one is on a different horizontal plane and turned a different way or something?
What is your data rate? Lower data rate = longer range (all else being equal).
I’m not really sure yet tbh. I haven’t gotten a prototype yet. It should be pretty low though. It’ll only send on demand, which is somewhat infrequent. The data consists of a single digit for a button press, in some cases the date and time, and occasionally the temperature. It’s not realtime data logging or anything. It’ll also listen for a master transceiver every 10 seconds or something to set the clock and send back data. I’m thinking under 10kbit/s will be fine.
Using a pair of the above PCB trace antennas (on the TX and RX) at a data rate of 9600bps, range is about 250 feet - with a BER of 10^-2. I don’t see how those antennas can be much more efficient than a chip antenna so I think you should be fine if you are looking at 10-20 feet range. I would do tests at up to 75-100 just to be sure though.
Have you considered using one of these [these? They are <$15 in singles and measure 9x16x2.5mm. (0.35x0.63x0.10in. - smaller than a SPLATCH antenna), operate at 915MHz, output up to +10dBm which should easily give you up to several hundred feet of range. Plus you don’t have to muck around with antenna and PCB design, etc. Also, you will not have to mess with getting FCC certification as the modules are already certified.
http://www.mouser.com/images/anaren/lrg/A1101R09A.jpg](http://www.mouser.com/ProductDetail/Anaren/A1101R09A00GM/?qs=sGAEpiMZZMu1CxYMhM6ijzzE9hicymgI)
I’ll definitely do some reading up on that wireless module you suggested. I’ll just have to do a cost/benefit on that though, cause it will save board space, but it’ll also cost more and require a redesign. Plus I’ll need to find code for the arduino, though at this particular moment I haven’t even looked into that yet. Failing that, I’ll probably go with the PCB antenna if it’s not significantly less good than a chip antenna, and cheaper. I’ll do some more research and post back. Thanks!
You do realize that if this is for commercial use (ie. you are making >5 pieces) it will require FCC certification if you are using your own design? If that is the case, then figure at least $6-10k and 3-6 months for this.
If you really want to reduce costs, replace the Arduino with a $1-2 microntroller and you will save more than going with your own RF design.
Even if I just use it as a drop in on a board? If this project is successful, I might end up making 30-40 of these total, as they come in pairs, not counting if I end up redesigning the board again. I didn’t mean I need to redesign the wireless board, just the host board it’ll be attached to.
If you use the Anaren module, you will NOT need FCC certification. With the RFM12B you will need FCC certification.
Well… crap… I guess that’s pretty much made the decision for me there, huh. No way am I messing with the FCC for what amounts to less than 2k worth of design.
As I mentioned earlier, replacing the Arduino with a $1-2 microcontroller, will save you the most money.
Like what? I’m running up against my pin limit as is on an ATMEGA328p.
static418:
Like what? I’m running up against my pin limit as is on an ATMEGA328p.
Boy, those ATmega328s sure are pricey. They have 23 I/O pins. I do not use Atmel stuff so I can only recommend going with a PIC (such as a PIC18F45K20) in a 44LQFP package which will give you 36 I/O’s. I am most familiar with 32-bit ARM MCU’s and for those I would go with an STM32F100C (in a 48LQFP) which costs less than either the Atmel or PIC with much higher performance.
I’ll try that in the future, but AVR programming is all I know at the moment. Learning a new language would totally blow the time frame for this project. I appreciate the suggestion though.
Looks like the the [ATmega32A is the same thing in a 44LQFP (32 I/Os) package.](http://www.atmel.com/dyn/products/product_card.asp?part_id=4404&category_id=163&family_id=607&subfamily_id=760)
Since that seems to be compatible in some roundabout way with the Arduino IDE, I’ll definitely have to consider that in future builds. For now though, I haven’t hit my limit with pins and the 328p is both cheaper and comes in a TQFP that I can actually solder. Since I don’t think I’ve actually specified what my project does, I probably should since that may help with advice. It’s basically a wireless mesh-able glove, with buttons, a real time clock, and between 1 and 3 shift registers depending on the model. I’m using the DS3232 i2c RTC, up to 3 daisy chained 74HC595 shift registers, and I was using the RFM12B transceiver, though I guess I should make a new thread maybe since I’m changing that? It’ll run off a boosted LiPo battery, and one hand will have buttons and a RTC, the other won’t. So I’ll have either 2 different boards or make sure I can just not add those parts.
As for microcontroller considerations, I suppose all I need really is enough I/O pins to run this stuff plus 3-4 extra at least for anything I might want to add. I also need a heap of program memory, at least probably the 2kb that the 328p offers, because I’m awful at programming and because the user selectable modes I’m implementing eat a ton of code space.
static418:
Hot gluing one on looks unprofessional. Even the backup battery for the clock will be non-removable and secured very well.
If you want to look professional, then be professional. If you are not a professional antenna designer, then find one. Just sayin’…
I am being professional. That’s why I’m researching it beforehand. As I said before, the tolerances for the antenna are huge. I just need it to look good. That’s what I’m after. It needs to look good and work. At any rate, I’ve decided to go with the other wireless module suggested earlier, which solves the antenna problem anyway.
Just a reminder: Here are the original “design specifications” for the OP’s wireless modules, taken directly from the first post:
Apparently, nothing has been built and tested, but we are getting testy about professional antenna design! That is quite an evolution.They should never need to work further apart than you can spread your arms. The highest power I would need is enough to have your arms spread and have to communicate on opposite sides of your body. The smaller I can make the RF bubble created by them, the better.
I didn’t mean to be testy. And a lot of it has been tested. I have this entire design working with the exception of the new wireless module. I’m nit-picking on the antenna design for two reasons. First, I’m trying to understand the “why” of all this. If I learn how it works, I won’t need to keep asking. The second is time. I don’t really have the time to keep redesigning this board. I need it to work the first time. That may be unrealistic, but I’ll put in as much effort as possible to try and make it that way. As such, and in keeping with the specs I need to adhere to, I can’t use a piece of wire hot glued to the board. The whole assembly needs to be surface mount, and as small as possible. Unless it involves the piece of wire. I gotta make that a sticking point. As I’ve chosen a new wireless module thanks to the information from jremington, thanks btw, the antenna should now be a moot point since it’s built into that module. And additional thanks to everyone who’s helped. I’ve gotten a lot of great info from this thread.