Hey guys, Im new here decided to join in search of some help. Im currently taking a coarse in college called electronic projects, I opted to build a FM radio circuit with an audio amplifier. This is very important its either pass or fail if I can get this working in time by the end of the semester, so I will even go as far as to offer a cash reward(paypal) to the person or persons who helps me get this working in time.

Ive got the circuit breadboard but Im having problems getting it to pickup an FM signal. Its being powered by a single 9V battery and ive measured around 7V on the main rail via multi-meter. The audio amplifier circuit portion seems to work just fine and i get a sound out of the 8ohm speaker that sounds as if it should. (The same noise as turning two way radios on without having any data transmit) The 10k trimmer pot increases and decreases the volume as it should.

Upon first construction of the circuit, I had put the TDA7000 in the wrong way. (Pin 1 was on the opposite end where it should be) Upon power on the chip got pretty hot. This likely could be my problem(I may have hosed myself), I have a 2nd TDA7000 on its way to test if this is the issue. For the turning of stations Im using a 3.5 turn adjustable coil as shown in the link. Whenever I adjust this manually it does not pickup any signal. I have got online and searched around and found another schematic that shows having a 100k variable pot, 100k resistor, and MV2105 varicap diode with a 1NF capacitor off pins #6. (shown here-http://electronics-diy.com/TDA7000_FM_Receiver.php) Is this really needed? I have decided to order these parts anyhow to see if it will help it get a signal, afterall Im at the point of trying anything before time runs out. Any help is greatly appreciated!

I decided to follow the schematic as show below from this site : http://electronics-diy.com/fm-radio-with-tda7000.php


My actual circuit as it is on a breadboard:

 

First thing is to find out why the battery voltage is sagging. My experience is that the LM386 performs poorly with a weak battery. Get a brand new Duracell, hook it up and measure the voltage; if it's noticeably less than 9V, something is wired wrong.

 

Hello,

Making an RF circuit on a breadboard is a bad idea.
Circuits upto 1 Mhz will work on a breadboard, above that there will be problems.
The connection lines of the breadboard will make capacitors that will ruin the RF signal.

Better use an other method to make the receiver.

Bertus

 

First thing is to find out why the battery voltage is sagging. My experience is that the LM386 performs poorly with a weak battery. Get a brand new Duracell, hook it up and measure the voltage; if it's noticeably less than 9V, something is wired wrong.

The battery measures 7.86V out of the circuit, the main rail is reading 7.7V with the battery connected. Its a new Duracell. Correct me if Im wrong but I dont think a new battery measures a full 9V?

The link also shows a supply voltage of 4.5-9V

 

bertus beats me to it.

Throw out the breadboard and find another way of wiring the circuit.
There is too much capacitance in that breadboard.

 

Hello,

Making an RF circuit on a breadboard is a bad idea.
Circuits upto 1 Mhz will work on a breadboard, above that there will be problems.
The connection lines of the breadboard will make capacitors that will ruin the RF signal.

Better use an other method to make the receiver.

Bertus

I have also heard this upon doing research, Im trying to test this circuit before making my own PCB and soldering in the components which still has to be done. What other method could I use to test?

 

I would say you have blown the chip up putting it in the wrong way, i would make the circuit using the varicap diode, instead of the coil, use veroboard instead.

 

I would say you have blown the chip up putting it in the wrong way, i would make the circuit using the varicap diode, instead of the coil, use veroboard instead.

Very likely, as I said I will test the new one when it comes. Also, theres a coil from pin #5 regardless, its just one link shows using a vericap diode with an extra capacitor and 100k pot and 100k resistor and the other link(which I followed) leaves these out.

I do believe the 100k pot and 100k resistor are used for fine tuning FM frequency.

 

Yes the varicap diode behaves like a capacitor when a voltage is applied to it, the smaller the voltage across it, the smaller the capacitance, the pot is used to vary its voltage, .

 

Yes the varicap diode behaves like a capacitor when a voltage is applied to it, the smaller the voltage across it, the smaller the capacitance, the pot is used to vary its voltage, .

Smaller voltage -> higher capacitance.

 

The battery measures 7.86V out of the circuit, the main rail is reading 7.7V with the battery connected. Its a new Duracell. Correct me if Im wrong but I dont think a new battery measures a full 9V?

Sorry, but you are incorrect. A new 9V battery will give 9V or slightly more.

You have almost zero chance of getting your circuit working on a breadboard. They are fine for low freq stuff, but at 100MHz stray capacitances will kill you. If you want to prototype this kind of circuit, the very least you should use is perfboard on a 0.1" by 0.1" grid. Keep the leads as short as possible and you might have some success.

 

Hello,

L1 and C1 will make the oscillator tuning circuit (VCO in the schematic).
Changing the value of either will change the frequency.
Normaly a variable capacitor is used, but a variable inductor will also work.



Bertus

 

Not only off the breadboard, but in little real estate, and cut down tracks on the protoboard.
The inductors are easy to ruin. I tried a breadboard first, then my second attempt on protoboard worked.

If you did get it working on a breadboard, you’d have incorrect inductor values for the finished board.

 

Hey guys, Im new here decided to join in search of some help. Im currently taking a coarse in college called electronic projects, I opted to build a FM radio circuit with an audio amplifier. This is very important its either pass or fail if I can get this working in time by the end of the semester, so I will even go as far as to offer a cash reward(paypal) to the person or persons who helps me get this working in time.

Ive got the circuit breadboard but Im having problems getting it to pickup an FM signal. Its being powered by a single 9V battery and ive measured around 7V on the main rail via multi-meter. The audio amplifier circuit portion seems to work just fine and i get a sound out of the 8ohm speaker that sounds as if it should. (The same noise as turning two way radios on without having any data transmit) The 10k trimmer pot increases and decreases the volume as it should.

Upon first construction of the circuit, I had put the TDA7000 in the wrong way. (Pin 1 was on the opposite end where it should be) Upon power on the chip got pretty hot. This likely could be my problem(I may have hosed myself), I have a 2nd TDA7000 on its way to test if this is the issue. For the turning of stations Im using a 3.5 turn adjustable coil as shown in the link. Whenever I adjust this manually it does not pickup any signal. I have got online and searched around and found another schematic that shows having a 100k variable pot, 100k resistor, and MV2105 varicap diode with a 1NF capacitor off pins #6. (shown here-http://electronics-diy.com/TDA7000_FM_Receiver.php) Is this really needed? I have decided to order these parts anyhow to see if it will help it get a signal, afterall Im at the point of trying anything before time runs out. Any help is greatly appreciated!

I decided to follow the schematic as show below from this site : http://electronics-diy.com/fm-radio-with-tda7000.php

I made a simpler circuit than the TDA7000 and it is much simpler and working great. At the same time you just need a button to auto-seek the FM frequencies within range. Antenna doesn't really matters if you are in range of reception.

 

Where did you get an old obsolete TDA7000? If from ebay it is a fake because they have not been made for many years and a long time ago were replaced by the TDA7088 that is in cheap Chinese radios sold at The Dollar Store.

I agree that a solderless breadboard cannot be used to make a 100MHz radio. I made thousands of prototypes soldered on stripboard after planning a compact layout. The strips were cut to be short lengths and reused and a few short jumper wires were used.

 

I have also heard this upon doing research, Im trying to test this circuit before making my own PCB and soldering in the components which still has to be done. What other method could I use to test?

You dont need a full PCB but you need to keep the high frequency parts off the breadboard, it could handle more than 1 MHz but the capacitance is notieable in the FM range, as such I think it is one of the main reasons the circuit doesnt work.

You can make a small plug in board, dont use the kind with lines on it what you need is points. The low frequency amplifier can go on the breadboard. you can use 2.54mm pin headers they fit into the breadboard.

 

Where did you get an old obsolete TDA7000? If from ebay it is a fake because they have not been made for many years and a long time ago were replaced by the TDA7088 that is in cheap Chinese radios sold at The Dollar Store.

I agree that a solderless breadboard cannot be used to make a 100MHz radio. I made thousands of prototypes soldered on stripboard after planning a compact layout. The strips were cut to be short lengths and reused and a few short jumper wires were used.

You are wrong or you have not encounter another IC that is way much better than the TDA7000. I made it successfully on breadboard and it works perfectly as shown on the video ...it require less than 10 component to make it work and it doesn't even need an antenna. I understand and found most circuit require certain antenna winding that make the job 100 times difficult not to mention the long hours of failing and all sort of special capacitors or varicap.

This circuit i made solely dependent on the IC and in fact the tuning does not require variable capacitors. Just by a switch of a button it automatically seek the channel based on certain frequency. The first time i made it's so easy like even elementary school boy can do

 

Hello,

Making an RF circuit on a breadboard is a bad idea.
Circuits upto 1 Mhz will work on a breadboard, above that there will be problems.
The connection lines of the breadboard will make capacitors that will ruin the RF signal.

Better use an other method to make the receiver.

Bertus

Agree with Making an RF circuit on a breadboard is a bad idea.

 

Agree with Making an RF circuit on a breadboard is a bad idea.

High frequency RF yes...but not with common radio i guess..

 

You are wrong or you have not encounter another IC that is way much better than the TDA7000. I made it successfully on breadboard and it works perfectly as shown on the video ...it require less than 10 component to make it work and it doesn't even need an antenna. I understand and found most circuit require certain antenna winding that make the job 100 times difficult not to mention the long hours of failing and all sort of special capacitors or varicap.

This circuit i made solely dependent on the IC and in fact the tuning does not require variable capacitors. Just by a switch of a button it automatically seek the channel based on certain frequency. The first time i made it's so easy like even elementary school boy can do

You do not have an old TDA7000 IC. Instead you have a newer BK1079 FM radio module that scans stations like a newer TDA7088 IC. The module has all the parts on it so the breadboard is not part of the circuit.