Andy Flind MFD.

[abdou2014]

another sensitive display for TDA

[Geo]

Before years when i constructed my first Andy's MFD i had connected a radio via a driver transformer. Now i plan to work a radio based on TDA7000 - LM386 and i am not sure if the output level is enouth to triger the beep generator.
Anyway... the experiment will shows .

[abdou2014]

direct connection lm386 and beep no, you must modify the beep generator or add a transformer , there is also a trick to know the variation of the input signal of the TDA without using the lm386

[Geo]

I believe that lm386 with gain = 50 is enoutgh. TDA7000 has audio output 75mv.Lets say a normal signal will give output 50mv x 50 gain = 2500mv.
2.5v signal is very very ok to triger the transistor before the 555. Also i can try gain = 200 at LM386.
No reason to connect 8R load to LM386.... a bigger one will be ok.

[abdou2014]

what is the resistance value in series with the capacitor for gain of 50

[Geo]

1K2 in series with 10uF

[abdou2014]

Thank you what's the coupling capacitor value did you use between lm386 and trannsistor of beep generator ?

[abdou2014]

I use 100nf , I believe it is better to convert the audio signal .

[abdou2014]

Originally Posted by Geo

1K2 in series with 10uF

I tried your values and i have 3.9 V at output .

[Geo]

Originally Posted by abdou2014

Thank you what's the coupling capacitor value did you use between lm386 and trannsistor of beep generator ?

100nF

[Geo]

Originally Posted by abdou2014

I tried your values and i have 3.9 V at output .

it's ok...

[abdou2014]

i thnk it's better to connect an auther detector with this coupling 100n

[humhum]

Geo , size of my FM Receiver is 50mm X 70mm small PCB (not use TDA7000 ) , in my test
I see that find my garden buried only from Nort and Nort-West way , but this small unit works only when use or mixing with groundet body energy .
About TDA7000 , need fine calibration of correct Frequency and Local OSC , this Freq can't
measure with any unit .

[Geo]

I am not sure that one other radio will do better work...... because i am not sure if it will work ok as sniffer. We want a sniffer out of FM band and TDA 7000 do this job very easy.
The main problem is the erratic signals by buzzer. We must keep it far from coil or must draw and construct a new beeper.

[Pahom]

Originally Posted by Geo

I am not sure that one other radio will do better work...... because i am not sure if it will work ok as sniffer. We want a sniffer out of FM band and TDA 7000 do this job very easy.
The main problem is the erratic signals by buzzer. We must keep it far from coil or must draw and construct a new beeper.

Geo what kind of coil are you talking about, a loop of 14 turns in a place with a 7000 tda or the receiving antenna itself?

[abdou2014]

Originally Posted by Geo

I am not sure that one other radio will do better work...... because i am not sure if it will work ok as sniffer. We want a sniffer out of FM band and TDA 7000 do this job very easy.
The main problem is the erratic signals by buzzer. We must keep it far from coil or must draw and construct a new beeper.

No , the second detector is for electric field can you show us a best buzzer circuit to avoid the erratic signals ?

[Geo]

Radio at 100Mhz is for electric field detection??? ... NO
Use a schematic with speaker....

[abdou2014]

Ok 100 Mhz for electric field , so the second must be for magnetic field , but at what frequency ?

[humhum]

Originally Posted by Geo

I am not sure that one other radio will do better work...... because i am not sure if it will work ok as sniffer. We want a sniffer out of FM band and TDA 7000 do this job very easy.
The main problem is the erratic signals by buzzer. We must keep it far from coil or must draw and construct a new beeper.

Now I will say Yes , Dear Geo , because have other radio type work better for sniffer
(without TDA7000 IC ) .
Also Andreas have in this forum small box (maybe 433Mhz) shniffer for find buried .
Calibration of TDA7000 is very critical fine tuning for buried Frequency .

[abdou2014]

I tried commercial radio and the TDA7000 is better , believe me

[Geo]

Radio is not the primary detector so don't spend so much time for it....

[abdou2014]

primary detector is the ANDY circuit, to begin , what is the resonance frequency of a receiver coil ?

[Geo]

There is n't magic frequency!!!!
Tune it near to 80Khz and its fine!

[abdou2014]

Thank you for your help

[abdou2014]

ANDY 4016 circuit has low output, almost I can't hear ringing, it is necessary to modify this stage and add something for speaker .