CB band transmitter using a microcontroller

[ina]

I need to design a low power transmitter that will transmit five
different signals to a receiver that is at most five feet away. I'm
doing the design for a client who insists on using RF instead of IR.

I'm designing the transmitter first and have decided to use ASK
modulation at a frequency between 20Mhz-30Mhz. The frequency is not
yet finalized. I'll have to research which freq is legal to use. I was
thinking of using a microcontroller to encode the five signals and
generate the carrier signal. I could create a square wave at an output
port and filter out a higher harmonic to reach the CB band but im not
sure if this is a sound idea. A RISC 8-bit controller could generate
an 8Mhz square wave and thus a harmonic at 24Mhz. The weak signal
strength of the harmonic may not be an issue since the max. distance
between the receiver and transmitter is only 5ft.

Does anybody think my idea is feasible? I'm new to RF design. Thanks.

 

[hamilton]

I need to design a low power transmitter that will transmit five
different signals to a receiver that is at most five feet away. I'm
doing the design for a client who insists on using RF instead of IR.

Hi,

When you says "send 5 different signals".....

Does this mean, you want to control 5 "relays, ports, bits...."

or do you want 5 differect messages to come out a serial port.

A garage door opener can send out many differect signals,
but controls only one switch.


http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=ASK+Transmitter&btnG=Google+Search

Here are a bunch of ASK transmitters, for only 5 feet....


I think you should take some classes on RF design.

 

[Tim Auton]

I need to design a low power transmitter that will transmit five
different signals to a receiver that is at most five feet away. I'm
doing the design for a client who insists on using RF instead of IR.
[snip]
Does anybody think my idea is feasible? I'm new to RF design. Thanks.

If you're new to RF design then don't bother with it. Buy a couple of
modules for $20 (less in quantity). They'll be pre-approved, work on a
frequency designated for this kind of thing and you can get ones which
accept and output logic levels that you can plug straight into a uP or
discrete logic.


Tim

 

[GPG]

I need to design a low power transmitter that will transmit five
different signals to a receiver that is at most five feet away. I'm
doing the design for a client who insists on using RF instead of IR.

I'm designing the transmitter first and have decided to use ASK
modulation at a frequency between 20Mhz-30Mhz. The frequency is not
yet finalized. I'll have to research which freq is legal to use. I was
thinking of using a microcontroller to encode the five signals and
generate the carrier signal. I could create a square wave at an output
port and filter out a higher harmonic to reach the CB band but im not
sure if this is a sound idea. A RISC 8-bit controller could generate
an 8Mhz square wave and thus a harmonic at 24Mhz. The weak signal
strength of the harmonic may not be an issue since the max. distance
between the receiver and transmitter is only 5ft.

Does anybody think my idea is feasible? I'm new to RF design. Thanks.

Google "rf remote control"

 

[Mike Harrison]

Google "rf remote control"

I rememeber seeing something on the net from someone who did something like this with the PICs
oscillator, using Sleep mode to control on/off - I think it was to do with rocket
telemetry/location.

Microchip do an RFPIC product designed for things like car alarm keyfobs, which incorporates a
transmitter, but I think it's UHF/VHF - have a look on Microchip's site

 

[Luhan Monat]

I need to design a low power transmitter that will transmit five
different signals to a receiver that is at most five feet away. I'm
doing the design for a client who insists on using RF instead of IR.

I'm designing the transmitter first and have decided to use ASK
modulation at a frequency between 20Mhz-30Mhz. The frequency is not
yet finalized. I'll have to research which freq is legal to use. I was
thinking of using a microcontroller to encode the five signals and
generate the carrier signal. I could create a square wave at an output
port and filter out a higher harmonic to reach the CB band but im not
sure if this is a sound idea. A RISC 8-bit controller could generate
an 8Mhz square wave and thus a harmonic at 24Mhz. The weak signal
strength of the harmonic may not be an issue since the max. distance
between the receiver and transmitter is only 5ft.

Does anybody think my idea is feasible? I'm new to RF design. Thanks.

I use units like these all the time. Both the transmitter and receiver
are under $5 each in single quantities.

http://www.mouser.com/index.cfm?han...uctid=446416&e_categoryid=132&e_pcodeid=50900
RCR-433-RP Radiotronix Embedded Wireless Modules Distributor - Mouser
Electronics - Electronic Component Distributor

Use a PIC chip at each end. The PIC16F628 as a built in UART. One at
each end and there is no limit to the number of control codes that you
can have. The range of the RF units is 100-300 feet.