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Measuring the frequency of a signal in a wire

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billericayboy

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Hi, i have built a mobile platform with two powered wheels at the front and a caster type wheel at the back so that it will travel around. There are whiskers on the front so that when it hits an obsticle it will reverse, turn and then go forward again. I now want to contain it in an area without walls.

My mother has a Mowbot which picks up a sinusoidal signal from a burried wire in the lawn and I thought that I could find out the frequency her robot uses so that I could run my robot inside her perimiter. This way I can consentrate on building a receiver and get it working without having to build a transmitter at the same time.

My Question :-

How do i find out what the frequency of the signal running round her lawn wire is ?

Any help would be apresiated.
 
Get a scope outside and hitch a piece of wire onto the probe to act as an aerial (antenna). Ignore the 50Hz or 60Hz mains signal that you will also get - I assume the frequency you are looking for will be higher than that.
 
i got this off the Mowbot site.

"The border wire creates a loop around your lawn which connects to MowBot’s garage which in turn is plugged into the mains. The wire carries safe electric current which MowBot detects as it passes over it, making it turn around and go in the opposite direction."
 
Thanks Dch & Willi.
1. I have borrowed a Frequency counter and will try putting a 1" coil of 10 loops on the aerial and see what frequency it picks up.
2. I tried the Mowbot people but they would not say what frequency was used. Hence why i need to find it myself.

If there are two signals being sent down the cable, will the frequency counter show them seperately or will it try to combine them. i have seen other designs using both one signal and others with two (one for border and one for returning to the garage).

I will measure the output and report back.

Thanks
 
Wow bananasiong, that is just what it does. Did you make the bot in the film ? what i want to do is find the frequency of the wire around my mother's garden so i can build a received to use her wire loop.

Any assistance you can give will be greatly received.
 
Ya, the perimeter wire is just a few loops of wires connected from the output of the 555 timer with a current limiting resistor. I made it to be around 10 kHz. Maybe your Mowbot is not using this frequency.
 
Hi, i have been sitting on the lawn with the Frequency Counter and apart form a wet bottom i have the following readings.

Frequency Counter Nikkai RP80
Coil 5 turns of 2cm diameter

Orientation 300Mhz range 3GHz range
in line 17Mhz 331Mhz
90% 25Mhz 300Mhz

but sitting at my computer here, i have turned it on and it reads

18MHz and 350Mhz

I then turned OFF the power to the Mowbot system and the signals were a couple of Mhz lower on the 300Mhz range anf 20Mhz lower on the 3Ghz setting.

I am confused as to what the readings mean and wonder if all i picked up was background readings.

Any suggestions

Thanks

Richard
 
I doubt it's that high, induction loop sys are normally low frequency or very low frequency, (30kHz to 300kHz or 3kHz to 30kHz). Your frequency counter starts at 300MHz which is far too high.
 
Hi, any idea how i can measure a lower frequency if this it too high.

I am at a loss how i can find the signal i require. i can do the mechanical / programming bits (albeit slowly) but the electronics bit is a bit of a mystery.
 
There are plenty of cheap frequency counters that work down to 0.1Hz, it sounds like you have an RF frequency counter.
 
Measure the signal at the "transmitter" e.g. where the wire loop goes underground.

First attach a voltmeter (so you know what you're dealing with) then the frequency counter. If you suspect that the signal is coded or there are multiple frequencies, use an oscilloscope.
 
Hero999 said:
There are plenty of cheap frequency counters that work down to 0.1Hz, it sounds like you have an RF frequency counter.

Hi Hero, thanks for the note.
I have looked for a cheap low frequency Frequency counter but can only see them from 50Mhz. Have you seen any that would do the job or any ideas where i should look.

Thanks

Richard
 
Check the specification, that normally means they go up to 50Mhz. You want one with a coaxial socuket so you can use it to measure circuits with too.
 
Hi, i have just orderer the following so hope to receive it next week.

9999Hz LED DIGITAL frequency panel meter with 4-DIGIT RED led display

Display type : 4 Digits, Red LED Display
Operating Voltage : 5V DC / 500mA
Frequency Range : 0 ~ 9999Hz
Accuracy : ±1Hz
Peak Voltage : <16V
Input Waveform : Regular Periodic Waves
Installation Type : Flush Mounting
Dimensions : 79mm × 35mm × 27mm


so i should have some more readings next week.

Thanks
for the help.
 
9999Hz might not be high enough, you ideally want something rated from <1kHz to >50kHz.
 
Hi the Frequenct Counter i borrowed was 1Mhz-gGhz.

If i understand correctly :-
1Hz = 1
1Khz = 1,000Hz
1Mhz = 1,000,000

I think i am looking for something between 50Hz and 80Hz. I will see what i get with this device, if nothing meaningful i will have to look at more expensive options.
 
You are correct but I don't think the system will be working at such low frequencies, it's more likely to be between 50kHz and 80kHz than 50Hz and 80Hz.
 
Reading at last

Hi, i am back. i received my IBQ2006ST Frequency counter in the post this morning and took a reading of the signal coming from the perimeter wire.

the reading was fluctuating between 73Hz and 80Hz with the aerial in line with the wire and up to 83Hz with the aerial at 90 degrees to the wire.
Could there be 2 signals going down the wire one in the low 70's and one up at 80Hz ?

I suppose i will have to build a receiver that i can tune into the frequency between 70 & 80Hz.

Any suggestions or offers of help with PCBs would be accepted - i have plans from a guy (his website) who has made one already.
 
Hi all, newbie alert !

Been reading this thread with some interest, would like to build a robot mowere myself.

I used to be an everyday software developer (macro assembler & C) but only got into electronics when I did my City and Guilds for Amateur Radio.

Billericay seems to be struggling a bit on the signal generator and receiver so thought I'd post this link up that I found a while back.

https://www.philohome.com/sensors/filoguide.htm

He's working around 50KHz Billericay so you may have a decimal point in the wrong place.

Wish I could find a little program to calculate how many turns of what gauge wire to make the 10mH inductors :(

Keep the responses coming guys, great thread.

Bob
 
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