TM 808 White's

[berreizeta]

I have changed the op amp from LM386 to a NE5532 and I think it works better.

Circuit :



Signal at CD4024 :



Signal Q1 to coil (6400Hz) :

[berreizeta]

Coils dimensions are correct ?

[berreizeta]

Some modifications:

Power Supply changed 78S40 -> MC34063



Audio Amp :



Audio Amp PCB :



Batt Meter Resistor :

[ata]

Hi berreizeta
Have you finished making 808? And please announce the results. Thank you

[pito]

To generate 6.5 kHz you can use attiny85 and this program

#include <avr/io.h>

#include <avr/interrupt.h>

 

void comp_match() {

  DDRB |= (1 << PB0);  // set PB0 as output

  TCCR0A = 0x00;

  TCCR0B = 0x00;

  TCCR0B |= (1 << CS00);   // No prescaling

  TCCR0A |= (1 << WGM01);  // Toggle mode and compare match  mode

  OCR0A = 75;              // Compare value can be calculated as frequency = Clock / OCR0A

                           // A value of 75 leads to about 108,6 kHz at a clock rate of 8150000 Hz

  TCNT0 = 0;

  sei();  // Enabling global interrupt

  TIMSK |= (1 << OCIE0A);

}

 

ISR(TIMER0_COMPA_vect) {

  PORTB ^= (1 << PB0);  //Toggling port PB0

}

 

void setup() {

  comp_match();

};

 

void loop() {

}

 

/*

    

    The expected frequency can be calculated as freq = clock rate  / compare value

    In this specific case the clock rate is around 8 150 000 Hz.

    (See frequency 81 kHz for compare value 100)

    Empirical data measured 2023-08-23 with a noname ATtiny 85 board

    compare value    Frequency

            1..37 -> 217.3 kHz  

               38 -> 211,5kHz  

               40 -> 201 kHz

               50 -> 162 kHz

               60 -> 135 kHz

               70 -> 116,3 kHz  

               75 -> 108,6 kHz  

               76 -> 107,3 kHz  

               80 -> 102 kHz  

              100 -> 81,8 kHz  

              200 -> 41,1 kHz

              255 -> 32,3 kHz

*/
​

[pito]

or 26.3 kHz,
I don't think the exact frequency is needed, the device can work between 5kHz and 8kHz

[pito]

On collector Q1 20V (on the bottom ), on Rx testing coil 0.2 V = 5 time less than in DD coils = not good.

[berreizeta]

Tested with Active XTAL 25.6Khz (6.400Hz) and Pasive Xtal 420Khz (6.535Hz) both works fine !

25.6Khz + CD4024 = 6400Hz
420Khz + CD4040 = 6535Hz

Little change on circuit for 420Khz (photo), original circuit s/schematic don't work for me ..

[berreizeta]

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

[berreizeta]

RX SIGNAL 14V :


PROBE COILS (6.533Hz) :

[berreizeta]

[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?

[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]

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.

[pito]