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'[PIC]: RF Tranceivers w/PIC (16F84/16F877)'
2001\02\11@225603 by Robert Shady

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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


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2001\02\11@232601 by David Huisman

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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

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2001\02\12@010402 by Mik Kim

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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


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2001\02\12@061416 by Malcolm Whinfield

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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}

2001\02\12@171155 by David Huisman
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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

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2001\02\13@085105 by Francois Robbertze

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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}

2001\02\13@093458 by Gordon Varney (personal)

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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).
>

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2001\02\13@101041 by Olin Lathrop

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> 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, .....olinKILLspamspam@spam@embedinc.com, http://www.embedinc.com

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2001\02\13@122108 by Jacob M Hartman

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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.

Best wishes,
Jake

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2001\02\13@124411 by Dan Michaels

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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

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2001\02\13@184615 by David Huisman

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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

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2001\02\14@172302 by Peter L. Peres

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Has anyone (but me) tried to send data using standard AM R/C gear and
standard (AM) R/C gear modulation (to stay legal) ? Experiences ?

Peter

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