# What do I need to transfer data from device A to device B? [closed]

Disclaimer: I have no experience or knowledge at this topic. I ask this only from curiosity.

I want to build two devices. Device A should send data to device B. Device B should display the received data on a LCD.

My question is: What opportunities do I have to transmit the data wirelessly over a distance of max. 100 meters?

I recently bought a Raspberry Pi and it fascinates me.
I started to get interested in electronics in general and thought about two devices (rasbperrys, arduions, w/e) which can send data to eachother.

I read about the possibility to send data via the 434 mhz band but I don't know what I kind of hardware/license (?) I need to do this.

## closed as too broad by Brian Carlton, PeterJ, uint128_t, Asmyldof, rdtscMay 14 '16 at 12:51

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Use device 'C' at the transmitter end and device 'D' at the receiver end. It should work fine. What those devices are depends on what 'A' and 'B' are and what the data to be transmitted is, but you haven't told us that. – Transistor May 13 '16 at 20:03
• So many things need to be added to even remotely give you an answer. Ignoring the LCD, which has no bearing on the problem, your question basically comes down to, how to do wireless communication. That itself is a giant topic and has many finer points. If this is an application question, possible power levels, bandwidth requirements, expected SNR (are there other potential transmitters in the area), is it a direct line of sight...etc would need to be answered. – Jarrod Christman May 13 '16 at 20:03
• Oh - you mean something like this archive.siliconchip.com.au/cms/A_112835/article.html or this circuitswiring.com/wireless-data-circuit-with-at89s52 or one of the other hundreds of articles you can google – JIm Dearden May 13 '16 at 20:07
• Conceptually it's like approaching me to build you a wall. You and I both have an idea of what a wall is, we know it's general purpose... but without more details of it's use and other specifics, you and I can't progress further in the discussion. – Jarrod Christman May 13 '16 at 20:08
• I added some details to my question, sorry! – Michael Pittino May 13 '16 at 20:17

You need to use a transmit/receive pair which are designed to operate with signals you can provide, and are licensed for use in the way that you intend. Most countries regulate the use of radio transmitters (even if you use unlicensed bands, you have to prove you don't interfere with other users).

You could use GSM, or WiFi. Both of these have cheap modules available, often used in electronics projects. Bluetooth won't reliably cover the 100m range.

You could also use a type approved VHF module, maybe narrow band FM. This would support a data rate of maybe 10kHz (and you would need to encode your data as a stream of pulses that the receive circuit could detect). If you investigate this sort of module, you will see the range characteristics. For one-off, a GSM module might be cheaper overall.

At 433 MHz, you can use this sort of module http://www.radiometrix.com/content/bim2a which is Type Approved for use in a limited way. You must comply with the operating perameters, you must not transmit speach/music (or digital versions therof). Commercial product or hobby, doesn't make a difference. You won't get a dedicated licence without exceptionally good reason, and without demonstrating competence.

If the comms is one way (A->B), you might be able to use a modulated laser targeting a photo diode. You can easily get handheld lasers that will reach 100m. You might need a few transistors in a breadboard and some wire. If you're not too fussed at the bandwidth, this should not be too difficult for a hobbyist. YouTube probably has a vid on something like that. It's a cool opportunity.

• You could also use an optic fiber shutter switch with the laser to pump the data, they can have response times of less than a nanosecond. Combined with a high speed silicon photodiode on the receiving end, you have a pretty high bandwidth one way system, barring any line of sight issues. You have to select a laser wavelength that won't cause issues for the detector in daylight. – Drunken Code Monkey May 14 '16 at 1:16
• @DrunkenCodeMonkey Good idea, but might that be rather expensive for someone "messing" about with Raspberries? I've just looked up a Thor labs kit for £1000. Fibre connections aren't cheap either. And how would you get a collimated beam in /out of the fibre? I was thinking of a transistor switching a 6V battery powered laser pointer. We're talking hobby here, not NASA. – Paul Uszak May 14 '16 at 13:06

Will there be many Device A? If there is just one, a simple 433MHz or 915MHz ISM band transceiver will work. But if there are many, keep in mind you will have to manage collisions and such, and in that respect you would be much better off with a mesh network, which you can easily implement with the excellent XBee modules from Digi. They are a bit more expensive than barebone transceivers, but you get the benefit of true ad-hoc plug and play, and the software stack is already implemented for you.

http://www.digi.com/products/xbee-rf-solutions