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Buried Wire Fence 11 Monate 5 Tage her #1650

  • Dave
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I am wondering why you choose 7.8Khz for the buried wire signal..? Is it possible to use say 38Khz.. If so what all would I need to change? Thanks...
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Buried Wire Fence 11 Monate 5 Tage her #1651

  • AlexanderG
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Hello Dave,

-A- Why did we choose 7.8 Khz?
1. A lot of China robot mowers use the same frequency (Tianchen, Supoman, and compatibles). So, you can use an existing charger station of them which includes a signal generator of the same frequency.
2. The signal generator should be simple - because it's simple, it generates a simple square wave signal with multiple harmonics waves. That means it generates not only the 7.8 Khz main wave but also additional waves:

7.8 Khz - 1st harmonic wave (100% amplitude)
15,6 Khz - 2nd harmonic wave (12% amplitude)
23,4 Khz - 3rd harmonic wave (10% amplitude)
31,2 Khz - 4th harmonic wave (9% amplitude)
39 Khz - 5th harmonic wave (8% amplitude)
...
101,4 Khz - 13th harmonic wave (2% amplitude)

You can see the harmonics in the frequency spectrum (2nd graph) below.


signal5.png



The higher you choose the frequency, the more chances are that your harmonics enter a wide range used frequency (ham radio, radio broadcasting etc.)

We are working on a more complex signal generator that does generate less harmonics.


-B- Can I change the frequency?
You can change the frequency of the signal generator and the resonator amplifier (resistor R and capacitor C) in the sender and in the receiver circuits:

1. Change the frequency of the tone generator in the Arduino sender code:
tone(pinDir, 7800); <--- that's the frequency of the tone generator (I think the max. frequency the Arduino library can generate is 31767 Hz)

2. Adjust the coil/capacitor of the sender's resonator circuit, so that you get a minimum impedance at your choosen frequency (or in other words that the resulting resonant frequency is your choosen signal frequency):

You can use a resonant frequency calculator for this:
www.lautsprechershop.de/index_hifi_de.ht...s/t_schwingkreis.htm
www.deephaven.co.uk/lc.html
www.1728.org/resfreq.htm

Example (when choosing the original 7.8 Khz):
R=10 Ohm (Resistor)
L=33 mH (Coil)
C=0.012 uF (Capacitor)
=> resonant frequency calculator result: the minimum impendance/resonant frequency is at about 7.8 Khz (7999 Hz)

3. Adjust the capacitor of the receiver's resonator circuit, so that you get a minimum impedance for your choosen coil (or in other words so that the resonator works best at your choosen frequency):

Example (when choosing the original frequency 7.8 Khz and the original L=85 mH coil):
R=10 Ohm (Resistor)
L=85 mH (Coil)
C=0.0047 uF (Capacitor)
=> resonant frequency calculator result: the minimum impendance/resonant frequency is at about 7.8 Khz (7964 Hz)
Energieverbrauch: 300 W (Bewegung) / 60 W (Stand-by), Freiheitsgrade: 100, Informationsübertragung: elektrisch, Anzahl Schaltelemente: 20 Mrd. (Parallelrechner), Gewicht Steuereinheit: 1,5 Kg, Version wird gebaut seit: 200 k Jahre
- Quizfrage: Um wen oder was handelt es sich? :)
Letzte Änderung: 11 Monate 4 Tage her von AlexanderG.
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Buried Wire Fence 11 Monate 4 Tage her #1655

  • Dave
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OMG ... Thank-you so much for the extremely prompt and very detailed explanation.. I am very impressed with this project.. I have been working on my own mower for the last couple of years and this part of the project really plagued me.. I did have a working version of the transmitter/reciever and it worked well this summer but I feel like this project as a whole is much more detailed and put together.. I will be redesigning my system to utilize this software/hardware..

I do have one more question on the topic.. If the sender is using a 33mH inductor and a .012uF cap for a resonant frequency of 7999Hz .. Why not just use the same inductor and cap for the reciever? Why build a coil to 85mH?
Letzte Änderung: 11 Monate 4 Tage her von Dave.
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