SparkFun Forums

[hudson]

I have read the data on the products page... but I'm trying to think of what kind of range I would get in a residential home? I think they say something about a machine shop... a warehouse.... those are slightly different environments than a regular old house =)? what if the insulation has that foil like material? Has anyone tested the range or implementing a project that could give me an idea?

[riden]

You can never tell for sure until you try it, but we have a tri-level with the receiver in the downstairs family room. I can clearly receive the data from my attic sensor and outdoor sensors about 75 feet away.

[hudson]

What sort of antenna are you using? are you using the SPE RF link modules? What sort of voltage on the transmitter?

[riden]

I'm using 2400 baud modules, a quarter wave antenna (about 6" of wire), and a transmitter voltage of 5 volts. One pair of modules are the SparkFun 2400 baud units, and the others are Radiotronics modules.

These modules work well in most situations, but as you can see from the various forum posts, there are things to be considered when setting up a link.

[hudson]

wow... it sounds like if I use the 13" (like 30-35mm?) and 12V it would kick over 100 feet?! Hopefully it will perform well going through multiple walls in my home. I'm trying to make my own home security system. Btw thank you and yes I'm using the basic SPE RF link module because I'm using pics to do the logic and stuff... probably some sort of time based burst packet mode protocol I will implement with error detection and addressing =).

[riden]

The biggest boost will come with powering the transmitter at greater than 5 volts (up to 12 volts, as you indicated). Because of the short distances involved, I'm not sure what improvement in range you will get using a longer antenna. However, using a 1/4 wave (6") or 3/4 wave (18") antenna will be a better impedence match for the transmitter allowing more of the energy to be radiated. I'd go with a 6" antenna to start.

There are a lot of forum messages discussing how to use these devices. Know that they DO work, but they aren't a transparent replacement for a serial cable. I use a simple comparator on the output of the receiver to act as a squelch circuit. Keeping the random noise suppressed takes some of the load off of the receiver PIC.

Also know that it takes a short period for the receiver to "wake up" and adjust its sensitivity, so you need to send sync bytes followed by a data stream that is as balanced as possible. Manchester encoding is not required, but would fulfill the balanced data requirement, as would sending the complement of each data byte.

[hudson]

what about the FCC is this legal with them? I dont believe the devices are advertised as being FCC compliant, but is it ok? I was talking to someone and said these devices may be in the middle of the ham band? I will search for other postings too thanks.

[riden]

what about the FCC is this legal with them? I dont believe the devices are advertised as being FCC compliant, but is it ok? I was talking to someone and said these devices may be in the middle of the ham band? I will search for other postings too thanks.

The 433.92 devices are in the amateur band traditionally used for low power communications. The 315Mhz units operate in the maritime and aeronautical spectrum. The rules for these devices can be found in the FCC regulations Section 15.231. The key is keeping the effective radiated power and the duty cycle (time transmitting, time silent) within the regs. Here is a paper that I found doing a quick Google: http://www.summittechmedia.com/highfreq ... urgess.pdf

[hudson]

Well I just wanted to thank you. I have done a lot of investigations. I foudn max stream / zigbee modules. They are in the price range of my security system... I don't need to fool around with FCC regulations they are listed under the FCC already. They also seem to do circles around and protocol I could cook up. Thanks riden =). Have you experienced the zigbbee modules? looks like they use AT commands...

[stevech]

I have used the MaxStream XBee and other vendors' modules. The XBees and XBeePro (be sure to buy the XBeePro if you can go the extra $ - much more range).

The XBee's can take a firmware download of either (a) plain old IEEE 802.15.4 where you address the destination node by its MAC address and there can be no meshing or relays; (b) load the ZigBee firmware where the mesh routing comes into play. Use (a) if your needs are simple point to point.

In either case you communicated with the module using serial data at the default rate of 9600Baud, or any rate up to 115000 if you reconfigure it. You can control it (say, set the destination MAC or NWK (ZigBee) address, using either AT commands or a binary mode. The AT commands are tricky, as you remember if you ever wrote modem control code: you send +++, wait just the right amount of time, then an AT command. The binary mode requires a lot more code but it's easier once it's done.

If your from/to addressing is static, say A talking with B, and vice versa, then you set the MAC addresses once using a dumb terminal program and forget it. From then, A and B exchange data on their serial ports- that is, it's a transparent serial-to-wireless-to-serial bridge, and bi-directional, with internal buffering and RTS/CTS flow control.

Pretty good for $20 @ 1ea (XBee) or $35 or so if I recall correctly, for the XBeePro.

There are at least 8 other modules on the market. I have a few of these. MaxStream is the best for the hobbyist. Sold by Digikey and Mouser.
I wish SFE would diversify - they have only the Jennic which is an odd-ball one.

[hudson]

I was also looking at radiotronix.com.

[riden]

Thanks riden =). Have you experienced the zigbbee modules? looks like they use AT commands...

You're welcome. I haven't used the modules, but I can see why you would want to use them. I agree that the modules take care of a lot of the nitty gritty and add more value than one-way data throw (i.e. guaranteed message delivery). I'll have to keep them in mind for a future project (maybe if I add more real-time wind speed/direction reporting).

[stevech]

802.15.4/ZigBee module vendors...
http://www.sparkfun.com/cgi-bin/phpbb/v ... 3885#23885

[hudson]

I'm reading through this FCC stuff and I'm trying to think is there an easy way to deal with it? I'm so confused... I'm working on a project that I want to ultimately try to sell... but I have to make sure it is ok with the fcc. has anyone gone through this process, if so can they briefly explain what they had to do?

[stevech]

if you use a module (not a chip) that's FCC type accepted, I don't think you have to re-certify, so long as the antenna and module configuration is the same as was type accepted.

Not so if you make your own PCB and use a chip rather than a module.

FCC Part 15 and SAR can cost, I think, $10K or more, from one of the accredited labs.