Hi everyone!
I'm doing a project wich involves some PIR-sensor arrays, each connected to an Arduino (Nano probably).
I need those sensors to transmit a simple signal when they detect movement; originally I thought of making a receiver with another Arduino, linked with one of those many rf/bt modules on the internet.
Recently I got a PMR radio (446Mhz)...
So the question is: wich module/trasmitter should I use in order to send simple "beeps" over the UHF band?
Some details:
I'm planning to use the "tone()" function and send it directy to a vhf/uhf transmitter.
Speaking of range, 200 meters will be perfect, but I wouldn't go less if possible.
The extendable frequency range of the receiver is around 400-480MHz, so the transmitter should send somewhere in that range.
Finally, I know that some frequencies can't be used for legal reasons, but some are free, and consider that the project is just for a small isolated local area (like I said, around 200meters), so it won't interfere with other communications..
Searching online, I didn't find anything suitable for this specs...I also thought of building a trasmitter on my own but, speaking of rf, is hard to achieve something good with home-tools.
Is out there a module that could do the work? Or maybe someone with a better idea...
Orion17:
Finally, I know that some frequencies can't be used for legal reasons, but some are free, and consider that the project is just for a small isolated local area (like I said, around 200meters), so it won't interfere with other communications..
There are indeed frequencies that can legally be used (license free) at specific powers.
But the situation of course varies depending on where in the World you are, and you dont say ........
Yea, sorry, my bad.
I'm from Italy and, from what I know, pmr446 are usable.
Anyway, you'r right sbout the "legal" stuff (wich is important indeed), but since my problem it's hardware-related, I wanted first to know if it's possible or convenient to realize such a thing and, befor that, why bother with burocracy?
Thanks for your input, by the way.
Well the RFM22B(Si4432) devices will cover that frequency range, there is Arduino libraries out there to drive it. It is an SPI based device.
The RFM22B works well enough as a tone beacon as one was used for the TUPOD Morse beacon that was launched from the International Space Station a week or so ago and that was heard on the ground, it was driven by a PICAXE with my software.
If the PMR radios will tune to the 434Mhz band, then you can use the license exempt ISM band, limited to 10mW, but you should hear that at 300M or so even in a built up area.
Cheaper UHF radio modules may not give you the frequency accuracy you need for narrow band FM receivers such as PMR and Amateur UHF handhelds.
I suspect you cannot use the PMR frequency bands themselves for the transmitter, PMR is likely limited to type approved devices.
Just a point, while you can use the licence free bands, you are not permitted to make a transmitter to use them. All transmitters must be type approved which is expensive for the testing and the paperwork.
The other thing to consider is the modulation, you can use FM, AM or AFSK. The latter being the most popular in the radio Ham bands.
