TM 808 White's

[berreizeta]

Adjust the coils to the minimum signal, without losing the frequency :

https://youtu.be/E_VlChTRuSI

[berreizeta]

Testing coils :

https://youtube.com/shorts/7IwzeES0-Zs?feature=share

[pito]

Rx coil should be with resonant capacitors, and moving Tx coil you need minimum at RX coil. On your picture is hard to see how coils are placed.

[pito]

Testing video inserting

You have to place video on youtube then paste the link to it in box insert Video, next to insert image box,

[pito]

A solution with 420Khz =



B:
DC Step up Hw-432, 7-12v to 16V

DC Step down HW-187, 7-12v to 6V

Voltage divisor LM324 on TM808 PCB.

One question: Is the use of 6V for the tip31c due to consumption or power level?

TIP331 is powered directly from batteries to separate it from rest of circuit, I believed that connector P7 is for speaker - it is very strange design.

[berreizeta]

At what point should the coils be placed, at the maximum or minimum signal on the oscilloscope ?

Coils at 66cm , signal direct from RX coil



I don't know how to upload a video here...

[berreizeta]

A solution with 420Khz =



B:
DC Step up Hw-432, 7-12v to 16V

DC Step down HW-187, 7-12v to 6V

Voltage divisor LM324 on TM808 PCB.

One question: Is the use of 6V for the tip31c due to consumption or power level?

[pito]

Coil perimeter 123.5cm (26.5*3.14+20+20) = a circle of 40cm diameter

Fixed op amp bias.


3V at 33078 out (pin 1), I think the coils should be 66.5cn from each other

You need to minimize this to millivolts , using aragment as on post #195, that is channel 1 oscilloscope to channel 2 connect testing coil and switch oscilloscope to XY mode, you should see respond to a can of coca cola from about 1 m away.

[pito]

On first pic, your 85 cm is 35 in my case, pic #2 this is how I am checking Tx power, only coil .

[berreizeta]

Coil perimeter 123.5cm (26.5*3.14+20+20) = a circle of 40cm diameter

Fixed op amp bias.


3V at 33078 out (pin 1), I think the coils should be 66.5cn from each other

[pito]

A can be replaced by stm32f103, B by 3x18650 battery.

[pito]

[pito]

If for testing you can use your yellow coil I can compare your transmitter with mine, for that I need to know also diameter of your coil and number of turns.
What is the value capacitors of the coils that you have ?
The last oscilloscope is telling that bias of the amplifier is incorrect, the pulses should be 50% duty cycle.

This arrangement allow you to check sensitivity (range ) of detector without additional electronics using just oscilloscope, for balancing move the coil back an forward.

[berreizeta]

My coils are not final, they are just to test the circuit, they are not perfect.

I do the calculation of the capacitors/frequency with:

https://ekalk.eu/lc_es.html

With the coil on the ground at 80cm, barely 1V reaches the circuit, and the preamp MC33078 needs a minimum of 1.6V)





With the coil at 45cm, it reaches enough for the preamp to act, giving about 13.5V

[pito]

Pito, join both coils at side, not at center. :

The red coil with green tape and LED is for testing how much power is emitted, Rx testing coil is under the table on the floor.

I have two questions.
1. What are the values of Tx, Rx capacitors
2. Can you put the yellow coil under the table on the floor while the Tx is on it?
What amplitude do you have on the that probe coil?