Let's Make Robots!

Radio emitter and receiver query

Hi all..

I'm new here so hello and be gentle!

I am looking into developing a small bot that could follow me around at a set distance (approx 3m) behind me. Ideally I would like to find a cheap pair of radio emitters and receivers that I could use to measure distance (2 small emitters placed on me and the receivers on the bot) This way I could separate the receivers on the bot to triangulate the position of me relative to the bot, this being used to guide the bot in my direction.
Are such things available as I can’t seem to find anything anywhere.

Has anybody done anything similar to this who could share some of their ideas or findings. I have an alternative idea as follows but it’s not as solid. Comments on potential issues would be greatly appreciated.

Use an ultrasonic range finder mounted on a servo or stepper that scans left to right until it finds a target (me) and returns the distance and angle so as to guide the robot. It is then continually scanning left and right at the target until it passes the target and then reverses direction and so on – this would give an angle range of the target with the direction being between the 2 extremes.

Thanks again for any help.

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Created by Bajdi here on LMR. Uses a Wii Camera which tracks IR leds and sources (you can watch the Camera in action on his channel). I'll quote him here from the shout box-

" no way, it's just a WiiCamera, simple sensor that detects IR light

Talks to the ATmega over the I2C bus, very easy to program

It's more advanced then a sharp

Aaronsuper1: It detects "blobs" of IR light and can keep track of 4 at a time, I believe?

The "distance" is the size of the IR source, it's not so accurate

but good enough to do some cool things :)

mogul: @bajdi simply put two IR leds on your transmitter, then you can get their distance and by that figure out your distance by triangulation

The WiiCamera gives a value between 1 and 6 for the size, you are not going to do accurate things with that"

So, simply put, it is not accurate enough but will do the job. Depends on how good a reading of size you get at your range.

Is there a solution to triangulating with RF or using sonar. Iam looking into this application and there seems to be quite a few commercial items like this out there now.

im pretty sure you can make a system that follows humans heat signitures cant you?

or maby have an infra red beacon on your shoe that it follows? also i think humans emit IR light from heat aswell if im not mistaken. supose you could look into that too


We reflect IR light, but the problem is that the skin can't reflect the IR alot, so a IR reciever wouldn't be able to really pick up the single really well. Only if the robot, was like a inch away from you but, if it would follow behind you. Then you might hit. But the main problem is that the skin wouldn't reflect it well enough. You would need reflective tape.

Hi all.

I have managed to find circuit diagrams for both an ultrasonic transmitter and receiver. Unfortunately I have little to very little knowledge of electronics and have a few questions regarding the circuit if anybody has time to have a peek.

The circuits

I think the circuits may be a little old as I am struggling to source the SL100 NPN & SK100 PNP transistors, will there be an alternative to these?
Also the relay is stated at 6v 200ohms I can only seem to find 6v 100ohms, will this be ok?
And finally the 560n ceramic capacitor, I also can’t seem to source this - would the closest to this suffice?

Maybe someone has an ultrasonic transmitter and receiver circuit diagram already that they could share with some more readily available components?

Thanks for any help !


• Plenty of alternative transistors will work for driving the emitter speaker
• The 100Ω relay will just consume more current, but will work the same
• That capacitor just looks like a filtering capacitor, anything in the neighbourhood will do the job

There are several pre-made ultrasonic units on the market, they may be more useful to you than trying to build your own, especially if your electronics skills need touching up. Have a poke around LMR and a few robotics parts stores and check out the options.

My TOBI will do something similar that you are wanting to do. I am going to be using 3 Ping)))'s and two IR on sweeping servos for distance detection, object avoidance and keeping the proper distance behind me or the next TOBI [in the chain] that it is following. For homing in on me, I am planning on using a Thermopile, IR Beacons and RF for getting a heading of my location [2 out of 3 provides a heading]. For the RF part I am going to use an array of 4 antennas that measure signal strength with reflectors to affect the signal.

My page is here: http://letsmakerobots.com/node/7025

A similar project is here: http://letsmakerobots.com/node/8527

Nice bot and very nice page! Thanks for the info..

Got a feeling from your trials and tribulations that this is going to be a little more involved than i first thought - A challenge no less !

This one uses IR LED's outdoors without (apparently) any problems http://www.shadowcaddy.com/index-UK.php

Edit: No it doesn't http://www.abc.net.au/tv/newinventors/txt/s2296849.htm click on "How it works" (hopefully you can see it outside Australia)



The Shadow Caddy follows a transmitter which sends out a radio frequency signal. The Shadow Caddy picks up the signal through two spaced apart antennas which are each linked to a receiver.