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Help modifying an FM transmitter circuit

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Danlab

New Member
Can you kindly check my PCB design for my project from your FM TRANSMITTER circuit. Your help is very much appreciated. Thank you in advanced.


Capture.PNG Capture1.PNG PCB.PNG
 

cowboybob

Well-Known Member
Most Helpful Member
Welcome to ETO, danlab!

Please provide a schematic for your circuit - it'll be a lot easier to read than transposing from your PCB (which looks good, BTW, at least at first glance...)

Also, please note that this thread is >12 years old. Might be best to start your own thread.

audioguru is still around. Not sure about draco_james
 

JimB

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audioguru is still around. Not sure about draco_james
draco_james was last seen here in August 2005.

Might be best to start your own thread.
If this discussion is going to develop, one of the moderators could easily split off the new posts into a new thread. (Looks like I could be talking myself into a little job there!)

My comments on the circuit board layout:
1 All the transistors appear to be the wrong way round. ie Collectors to 0v line.

2 The 0v line is isolated from the mass of copper marked ground. It would be better if the ground absorbed the 0v line.

3 interesting use of terminal blocks to represent a coil.

JimB
 

Inquisitive

Super Moderator
New thread started.
 

JimB

Super Moderator
Most Helpful Member
Well done!
JimB
 

audioguru

Well-Known Member
Most Helpful Member
Danlab sent me a "conversation" asking if a line level stereo to mono input modification of my FM transmitter could use a microphone. Since I cannot attach anything in a "conversation" I asked him to make a new thread in the forum.
Here is my FM transmitter with an electret mic and it was made on stripboard. Also here is a pcb of it that I never checked.
I tweaked its parts values to get a very good RF sinewave.
 

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Danlab

New Member
Thank you for answering my questions guys. Starting to build the transmitter.
However, the voltage regulator LM2931 isn't available here. Can i use LM1117 or LM7805 as a substitute? Will it work the same? Thank you very much for your help
 

audioguru

Well-Known Member
Most Helpful Member
The voltage from a 9V alkaline battery is 9V only when it is new and has not been used. Its voltage slowly drops to 4.8V when it is said to be dead.
The LM2931-5 is a low dropout 5V voltage regulator that still regulates when the input from the 9V battery has dropped to about 5.25V.
A 7805 stops regulating when its input has dropped to about 7V which happens soon.
An LM1117 stops regulating when its input has dropped to about 6.1V.
Low dropout regulators need a pretty high value output capacitor for stability as shown on the datasheet.
 

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