Transmitter-related project question

Thread Starter


Joined Oct 17, 2007
I'm designing a project involving an automated robot (or, robots) which follow a course indicated by a series of RF beacon nodes. I intend for the nodes to be as small as possible, and they would plot a course for the robot to follow, in sequential order, such as:

node1 - node2 - node3- ....

The nodes would not transmit any data other than beacon signal. The robot would then detect the signal using a directional antenna and proceed toward it, switching its focus to the next beacon once it reaches its destination.

The problem that I predict will arise stems from when I want to "run" multiple robots at the same time, along the same course. This means that ideally each beacon will be transmitting continuously, so that any robot on any step of the course will be able to detect and direct itself toward the beacon. (Robot A may be going to node1, while robotB may be going to node 7) The simplest way to do this would be to have each beacon transmitting on a different frequency, but that runs me in to another set of design problems. Aside from buying different transmitters with different manufacturer set frequencies (which would severely limit the amount of nodes I could use), is there an easy way to do this? Building the transmitters myself using variable coils would likely be too large for a practical beacon.

Is there a simple solution? I've tried looking for a voltage-controlled variable frequency transmitter, but haven't had much luck as of yet.

Any suggestions or advice would be greatly appreciated, as the project is still in its development stage.


Joined Aug 15, 2007
When there were several lighthouses in an area, they would flash at different rates, and sailors could tell which was which by the flash pattern. So if all beacons flashed at different rates which were NOT multiples of each other, that might work.

Or, what if you mixed DTMF tones into the radio signal, and then decoded them on the robot? Basically, what radios do all day long when the transmitters mix music and/or voice with the RF frequency, and receivers convert that back to sound for the listener.


Thread Starter


Joined Oct 17, 2007
Having each node have a unique frequency definately seems to be the way to go, but I still don't know how I would go about varying them. Remember, I want to keep the nodes compact, so unless I can get a built version really small, I'd have to go with some kind of manufacturer made transmitter. And that's the problem, as I can't seem to find one that will transmit on variable frequencies.

Sending DTMF tones would be great, except that with all the nodes transmitting, the signals would just overlap the robot would have no way of differentiating between nodes to find out where to go. Using different frequencies would allow it to focus on one signal at a time and determine direction via a directional antenna. Or, at least that was the plan.

Appreciate the continued suggestions!


Joined Jul 17, 2007
Take a look at Linear Technology's LTC6908 series IC's.

6-pin SOT23 package oscillator, programmable from 50kHz - 10MHz using one resistor. Just feed it somewhere between 2.7v and 5.5v, and connect an antenna to one of the two outputs. For that matter, you could use a switching device to select various values of resistance to change the freqencies.

Doesn't get a whole lot easier than that. ;)

For your receivers, you might take a look at ZN414 IC's - they're an AM receiver in a TO-92 type package; 150kHz-3MHz. Philmore stocks them uner #86-1007, but you can find them lots of places. Google is your friend here.
Needs some resistors, a coil and a few caps for external components, but it's really quite simple.

You might be able to mod the circuit so that you could use a varactor diode to change the frequency.

[edited to add the following]
Look at Kit 63. It uses that same ZN414/MK484 chip. MK484 was the original version of the IC; the ZN414 is a copy. I don't think the original MK484 is made anymore.