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Wireless options; Where to start?
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Wireless options; Where to start?

by zedin on Thu Feb 07, 2013 1:43 pm

So I want to make a project that uses wireless but unsure where to start.

The basics of the project is often I get home first and use headphones on the computer. I don't hear when the wife gets home but I like to greet her and see how her day went. For fun I want to make a sensor (probably just an ultrasonic rangefinder) that detects when her car is in the garage. I then want to wirelessly transmit that info to a reciver hooked to my raspberry pi which dynamically updates a webpage to say she is home. Ultimately I want to figure out how to make a popup on my windows machine when the state changes but for now trying to keep it relatively simple.

So my basic question is what sort of wireless option would be a good beginning point to hookup on the raspberry pi and sensor circuit to have the pi read in on the GPIO when the sensor says she is home.
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Re: Wireless options; Where to start?

by adafruit_support_mike on Thu Feb 07, 2013 6:21 pm

I'd say the Xbee ( http://www.adafruit.com/products/128 ) or the Electric Imp ( https://www.adafruit.com/products/1129 ) would be your most likely choices. The Xbee has been around longer so there are more projects out in the world using it, but the Imp looks like a nice little device. I doubt the 'engineering history' advantage will last for long.

Those are at least a couple of options to get you started.
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Re: Wireless options; Where to start?

by tastewar on Thu Feb 07, 2013 8:40 pm

Unless I'm misunderstanding, one of the big disadvantages in Electric Imp is that it requires talking to their website. Now, for this particular exercise, that's not a stretch -- the OP already wants to use a web page for notification. But what if he later on he wants to blink the lights in the living room instead? Relatively straightforward with just Arduino + XBee (says the guy who has yet to do an XBee project...). A shame to have it not work just because we lost connectivity to the internet (horrors!). And what if this great, innovative startup goes belly-up? What happens then to all the cool devices people have built? What about my Budweiser Red Light? (not a hockey fan, but if I were, this Electric Imp enabled item would be irresistible: http://youtu.be/-sDN8I2O8kk)
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Re: Wireless options; Where to start?

by EasternStarGeek on Fri Feb 08, 2013 10:09 am

True, there are a bewildering number of choices out there, but I think the XBee is one that gives you the most bang for the buck. Granted, they are not exactly cheap, and you can make your SEWS (Spousal Early-Warning System) much more cheaply with simpler hardware, but I recommend the XBee because I guarantee that once the wireless bug bites you, you'll want to do more and more other things, especially after she catches on to what you are doing and makes you take it down!

Just a few things I like about that platform:

1. Lots of on-board connection choices- TTL serial port, discrete digital I/O, and analog inputs (last time I looked, XBee series 2 does not support analog outputs, but it is possible with the on-board hardware with future firmware)

2. Several different operational modes:
(note- modes are determined by the firmware you load, and are mutually exclusive. Pick the one you need- you can always change it later)
a. Direct transmission of digital I/O states between transceivers, without the need for a host microprocessor on each end.
b. Serial Port pass-through, basically a two-way dumb wireless serial "cable."
c. API Mode, which allows you to package your data into telegrams with robust transmission and data integrity verification. API Mode also allows you to do a whole host of other things related to the configuration and operation of the device itself. (requires a smart host to build and decode the data packets. Arduinos are great for that)

3. Function is determined by firmware, which makes the XBee fairly future-resistant.

4. Series-2 XBees can be used to build mesh networks (tres cool!) which is a great way to extend the reach of low-powered modules.

5. Can be exposed to the Internet, via a dedicated Gateway module (separate hardware, also mfg by Digi, the makers of XBee)

If you decide to get started, here are some tips:

1. Brace yourself (and DW). Playing with XBees is like eating potato chips. It's very difficult to stop.

2. Buy the regular Series-2 modules. No need to get the Pro units (extra power and range). You'd be amazed at what the "regular" ones can do.

2. You will need at least two, but buy three. Trust me. (Note Series-1 are point-to-point only, and do not support mesh networking)

4. Because of the wonky 2mm pin spacing, you will need a breadboard adapter for use with standard 0.1" breadboard grid. There are many interface boards out there, but the best one, by far, for beginners is this one:
https://www.adafruit.com/products/126
it's very well-designed, with a lot of useful features, and worth every penny!

5. For configuring your units, you will need a TTL to serial adapter, such as:
https://www.adafruit.com/products/70 or
https://www.adafruit.com/products/284
They both are functionally equivalent, and will plug directly into tha Adafruit adapter board, a very useful feature!
The Firmware configuration and setup is accomplished with a software tool (X-CTU) that you can download and use for free from Digi.

and finally, perhaps most importantly...
https://www.adafruit.com/products/963 The definitive XBee Reference Manual. I have had my worn, dog-eared copy for over a year, and I still use it regularly.

These things are a blast, and if you have the budget, loads of fun!
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Re: Wireless options; Where to start?

by zedin on Fri Feb 08, 2013 11:54 am

Thanks for the info. Will probably get the xbee. They seem a bit pricy for what I want but I think once I get the hang of it I might be able to swap out the wireless for something simpler since all I really need to do is send state changes.
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Re: Wireless options; Where to start?

by Zener on Fri Feb 08, 2013 6:12 pm

The Xbee is a great product, but I think it is overkill here since there is no data to transmit, and the range is short. You might consider:

http://www.adafruit.com/products/1095

and

http://www.adafruit.com/products/1096

Total cost, $12

You will need to hack it a bit but not too bad. That should get the signal to your Pi.
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