Hey guys, fairly new here to DIY/MCU/Make-ness. I’ve started with Arduino, got a coupla cool projects planned, schematic’d, and pseudo-coded. Now I’ve got something really cool that I am DEFINITELY going to need some assistance with.
I’m sure someone’s done this before, so if anyone knows of anything, a point in the right direction would be awesome. Here’s the concept:
For Valentine’s Day, I want to make my girlfriend and I a set of jewelry, a necklace for her, and a bracelet for myself. Both items will have some sort of MCU (Probably an ATiny), a wireless transceiver, and an LED. The idea is that the closer in proximity the two are together, the brighter the LED shines. (Insert “aww” here, then read on).
The LED shining is the easy part. What I want to know is, is there an easy, semi-affordable way to implement this kind of ‘distance sensing’ via any of the wireless options SparkFun has available? I’m looking to Nordic, but having never used it before, it’s obviously intimidating. Does Nordic (or FM, etc.) have something similar to Wi-Fi’s “Signal Strength” that I can use for this? Thanks guys.
I am not familiar with the Nordic, but the XBee V1 (which SFE carries) definitely has an RX-strength indicator. Sadly, the module is too large for any kind of jewelry use (about 1" sq), but the capability is there. You need to use the module in API mode (versus transparent mode) to get the signal strength. I would expect that other RF modules have similar capability.
For this I would go with one of the very simple OOK/ASK transmitter/receiver pairs (a key fob tx/rx modules may work). Then dig into schematics for radio receive field strength meter circuits and adapt it to drive an LED.
Another issue is battery life. Transmitters do take a few mA so I don’t know how long a tiny battery w
@Vraz…I considered XBee, but you’re right, the size is JUST too big to fit in my project (once adding the extra components)
@leon_Heller: Nordic seemed like overkill anyway, though the nRF24L01 (Not the same as the nRF2401A SFE carries) DOES have an option for reading signal strength. I’m not sure which TI/Chipcon devices you’re talking about. Could you link me?
@waltr: I wiki’d OOK/ASK. Looks promising. Any idea where I can get some (without tearing open a key fob like SFE does ;)…)
For some reason, my comment is still awaiting moderation (said “damn”).
@Leon, that looks good. Also, the nRF24L01+ has it, not just the regular nRF24L01. My B.
@Stevech: Just curious, why won’t TOA work? For this project, we only need a rough indication. We don’t need precision, obviously.
@TheDirty RFM12B looks very promising as well. Again, signal strength will work just fine for this project. It doesn’t need high precision, just a general idea.
EDIT: Hot damn, the RFM12B is ready to provide clock signal to MCU too. Cool!
TOA is based on a common reference time. So that relative delta or absolute time can be calculated. To a few nanosec - RF propagates at about 1nSec per foot.
Looks like I’m going with either the RFM12B or the CC2500. Definitely NOT the Nordic nRF24L01+, since a re-read of the data sheet reveals the Received Power Detector only has two states, high or low, depending on if the reading is above -48dBm. Obviously NOT going to help here.
Yes, the CC2500 is just a bare chip. Does TI have eval boards, or are they third party? Either way, where can I find them? Trying to order samples right now but the site is in shambles, getting all sorts of weird errors.
Looks like that may be the winner, actually. It’s a damn shame there’s no samples, but fortunately there’s TWO boards in there. Just wonder if the size is going to be too big. But I doubt I could shrink it any less. My initial plan was to etch my own board (using the laser printer/copper board/etchant home method) and use it, then Ponoko the enclosures (which I’ll still be doing). The really nice thing about this kit is it’s essentially a fully-loaded wireless Arduino in a sense: Completely inclusive, cheap, fairly straightfoward. The added bonus is the whole TI MSP line is uber-low power. Looks like we’ve found our winner. The datasheet includes an algorithm for reading the RSSI as well. Thanks guys…I’m going to be pestering the hell out of this forum to help me set it up, now.
Yes, that’s the RF2500, which I have. It’s both the microcontroller and the CC2500 itself, so assuming you are okay with using the MSP430 then I can’t see it getting any smaller than that. Microcontoller, RF transciever and chip antenna on a small board.
2 MCUs, transceivers, and chip antennas, plus programmer, all for $50.
Technology is amazing. Can’t imagine anything better than the MSP for this, with the low power consumption.
Anyone got any experience with MSP programming? I have a feeling I’m going to need to take this somewhere smaller like Google Wave or something.
EDIT: Just ordered. On the upside, AvNet has a dev competition going on for the MSP, and has a 25% off coupon for any MSP-based products (The RF2500 included). On the downside, I won’t have the product in time for the competition deadline or V-Day, so this project just turned into a one-year gift. Which is actually probably better, since I have a tendency to get ahead of myself and rush anyway…dumb***…Ordered some neat stuff with my SFE gift certificate today, including the blinking Christmas tree kit for soldering practice. Excited.
I personaly woudn’t try those QFN packages on homemade PCBs, as the lack of soldermask would drive me crazy. Also, such RF circuits really need a proper 2-layer PCB with plenty of vias in the right places. I’d suggest using BatchPCB or Olimex if you’re only getting a few boards made.
BretMattingly:
Anyone got any experience with MSP programming? I have a feeling I’m going to need to take this somewhere smaller like Google Wave or something.
I was wondering about my own intelligence there. Usually when I get an idea for something I haven’t done before, I get way far ahead of myself. Such was the case with my first Arduino project, a piezo-triggered MIDI controller. I’d never properly learned to solder. I ended up sticking my MIDI jack on there with no way to get it off. (FAIL). Such would’ve probably been the case with this one. I’m actually glad there’s an 8-week lead time, I’ll use my new ‘deadline’ to brush up on soldering, circuit design, EAGLE, etc.
