Post by thread:[PIC]: RF Tranceivers w/PIC (16F84/16F877)

I have a project that requires two way RF communication between my PIC board and my computer. I'm wonder what experiences anyone out there has with this situation.. I've found about a dozen products that look like they would work with a significant difference in price (anywhere from $7.50/ea up to $300/ea). My "requirements" in order of preference are: 1. At least 50 Kbps (for near real-time compressed pics of course!). 2. At least 300 foot range (indoor through walls, etc). 3. As inexpensive as possible (ideally under $100-$150 complete). Then the optional... Increase #2 as much as possible (I've seen ranges up to 5 miles, which would be ideal, but those are the ones that where $600/pair). Any help/input/experience is greatly appreciated... -- Rob __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail - only $35 a year! http://personal.mail.yahoo.com/ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Robert, Take a look at our site. http://www.orbitcoms.com/rf_modules.htm The TRX2905 FSK, UHF transceiver module will do the trick Up to 115k Baud. Typical 300m range USD$26.30 (1 up) We will also be publishing details of a PIC based controller for this module in the next 1-2 weeks that integrates the TRX2905 with a PIC16F876 and provide all over-air firmware, Analog inputs, digital IO and Serial comms. Regards David Huisman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Just out of curiosity, why do those "long distance" units cost so much? Do they require special licensing from the FCC? I'm also curious if there are any "faster" burst rate devices that are cheap. I'm looking for 1 Mbps or more for 1 sec, then nothing for 10 sec. If FCC was the issue, would such device be cheaper? TIA For 115kbps, I found some at http://www.orbitcoms.com/rf_modules.htm --- Robert Shady <spam_OUTpicnewbieTakeThisOuTYAHOO.COM> wrote: {Quote hidden}> I have a project that requires two way RF > communication between my PIC > board and my computer. I'm wonder what experiences > anyone out there > has with this situation.. I've found about a dozen > products that look > like they would work with a significant difference > in price (anywhere > from $7.50/ea up to $300/ea). > > My "requirements" in order of preference are: > > 1. At least 50 Kbps (for near real-time compressed > pics of course!). > 2. At least 300 foot range (indoor through walls, > etc). > 3. As inexpensive as possible (ideally under > $100-$150 complete). > > Then the optional... Increase #2 as much as possible > (I've seen ranges > up to 5 miles, which would be ideal, but those are > the ones that where > $600/pair). > > Any help/input/experience is greatly appreciated... > > -- Rob > > > __________________________________________________ > Do You Yahoo!? > Get personalized email addresses from Yahoo! Mail - > only $35 > a year! http://personal.mail.yahoo.com/ > > -- > http://www.piclist.com hint: PICList Posts must > start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other > [BUY]:,[AD]: ->Ads > > __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail - only $35 a year! http://personal.mail.yahoo.com/ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Low Powered transmitter in most countries do not require licencing. Although beware, these have strict O/P level requirements before they have to become licenced systems. 300ft or 100m range is dependant on a number of factors. Bandwith: higher the bandwith the lower the range. Area: Most distances are usually perfect conditions, Line of sight etc. Antenna: This is the most critical, directional antennas will give you more range possibly more than 300ft line of sight. but a helical may only give you 60ft-100ft.This could be reduced even furter if the Baud rate increases. The higher the frequency the smaller the antenna. Most product specs are usually set for the absolute maximum and need to take into consideration a number of factor. Inside wall, metal stucture stucture support, even the metal particals in the brickwork can affect the practical range of a TX/RX. Most product specs are also based on low baud rate setting. See if the product specs display graphs relating effective radiating power versus bandwith. Couple of other sites you can look at regarding modules are http://www.rfm.com and http://www.lprs.co.uk These sites I know have comprehsive gain specs on various antenna arrangments. I am currently in the middle of a project involving RF Transmitter and Receiver modules. I have found produced products usually have a range of 60 metres or 120ft or less. Regards Malcolm Whinfield {Original Message removed}

Mik, Usually when you talk "long distance" (say greater than a couple of km), the devices require higher power. The power required usually exceeds the allowable maximum for the unlicensed band. Now the unit has to be licensed, it also has to be subject to testing to the standards for the frequency band you have chosen to operate within. The standards are far more stringent than those for unlicensed. This means the design process is far more extensive, the component costs are more expensive (due to having to meet all the additional specs). The investment costs are higher as someone has to pay for the local testing body to test the device type (Type Approval) to the standard and issue a certificate of compliance. And guess where these costs are recovered ... that's right ! in the price of the unit. Even for unlicensed equipment, the performance (and range) differ dramatically. There are many "garage door opener" technology based solutions that may be good for 100-200m but you must look carefully at the specifications. The stated range for lower cost units is quite often the Free-Space, Line of sight best case (i.e.. if the two units were lifted 1.5m in the air in an empty field, then on a good day, the unit 100m away will receive the transmission). When comparing performance of radio modules. Look at the defined BER (Bit Error Rate) and Sensitivity. A radio with BER of 1e-3 at a sensitivity of -110 dBm would be great. But a unit with BER of 1e-2 at -90dBm would not be so hot. Note: BER of 1e-3 means that if you transmit 1000 bits of information, statistically there would be 1 error. Our preferred solution is an RF module with controller board .. As explained on our site page http://www.orbitcoms.com/rf_modules.htm If you look at http://www.orbitcoms.com/rf_module_intro.htm , I discuss some of the issues. Regards David Huisman -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Dear David Huisman Just a dumb question! I know that some telemetrie systems use normal two way radios... How do you connect a pic to a two way radio? Do you need a interface between the analog input (microphone) of the radio and the pic(Tx) and again from the speaker to the pic(Rx). Are there dedicated IC to do these work. I heard ones that there are IC's that do error correction etc. so you don't have to worry about that in the pic and they do the data transmission for you. Can someone help me with a manufacturer... Are the connection to the pic different when using a 'data" transceiver Regards Francois {Original Message removed}

The best way is to FSK the transmitter. This will require you to interface the main osc, or PLL if used. To receive the FSK signal you will need to access one of the IF stages. I don't recommend this unless you have a strong RF background. Actually, using a Two-Way radio for telemetry is very easy. You can send data through the microphone and receive it through the speaker. The data rate is a little slow however. Output one pin of the pic into a circuit that will convert a square wave audio to sine wave, then attenuate the signal to the microphone audio level. generate a 1000hz tone for a logic level zero, and a 2000hz tone for a logic level one. Another simple circuit in the receive to convert the sine wave to a square wave , and measure the frequency being received. Some what simple but it does work. Gordon Varney > How do you connect a pic to a two way radio? Do you need a > interface between > the analog input (microphone) of the radio and the pic(Tx) and again from > the speaker to the pic(Rx). > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> How do you connect a pic to a two way radio? Do you need a interface between > the analog input (microphone) of the radio and the pic(Tx) and again from > the speaker to the pic(Rx). > > Are there dedicated IC to do these work. I heard ones that there are IC's > that do error correction etc. so you don't have to worry about that in the > pic and they do the data transmission for you. Can someone help me with a > manufacturer... > > Are the connection to the pic different when using a 'data" transceiver You can buy off the shelf radio tranceiver modules that present something like an RS-232 interface at each end. When using these you have to consider the very real chance of bit errors. Bluetooth is something to look into for short distances. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, .....olinKILLspam@spam@embedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 12:19 PM 2/13/01 -0500, you wrote: >Thank you, David, for the pointer to your RF modules. For what additional >impetus it's worth, I'd definitely be interested in seeing the details of >the TRX2905 / PIC solution before committing to that RF module and buying >some. > I put up links to a bunch of RF modules, including David's: http://www.oricomtech.com/teklink2.htm#RF2 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Francois, Firstly, let me assure you.. that is not a dumb questions. Nearly all questions are valid.. this is how we learn new things. The RF modules are not the same as two-way radio (as we may commonly refer to them). I would generally consider a two-way radio as an analog, voice communications device. You can send data using these but you would normally require a modem (modulator/demodulator) to convert the digital signals from your PIC to the analog signal transmitted via the radio. The RF modules at http://www.orbitcoms.com/rf_modules are designed for direct digital communications. The module itself handles the digital to rf and rf to digital transformation. (It uses a scheme known as FSK. - Frequency Shift Keying ). To use an RF module alone you need to understand some of the concepts of RF communications (especially in the area of packetization of data, error handling and DC signal balancing to name a few). The modules are great for those with this experience who just need the RF functionality to add to an existing product that has a micro controller and some I/O lines to control the RF module. Imagine the RF module as a motor in a car. The motor still requires fuel and control lines (such as accelerator cable etc) to be useful. To assist those with little or no RF experience, we have developed a controller board that has the RF module built-in to it. The controller board has a PIC16F876 micro that handles all the hardware functions required to operate the RF module as well as having all the over-air radio transfer firmware, Analog Inputs, Digital I/O and a serial link to your application. This means you can send and receive data simply from a PIC using standard TTL serial data. You can also configure the controller to perform certain automated tasks via our Windows utility program. You can configure the units with node numbers to operate as a radio network, you can configure them to do task that operate stand alone like... read the Analog ports every 2 seconds and send the results by RF to node number 3. If you go to http://www.orbitcoms.com/rf_module_intro there is a brief overview of the various levels of rf solutions that will help you decide what solution best fits your rf experience level, cost and application requirements. I will shortly add a comparison table to this page also. Regards David Huisman -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.