Yea, very similar. High quality electret mic
The solder of one of then pins is connected to the metal case if look clearer.

Thanks.

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Hi,
Can I use 5 volts for the whole circuit? By moving the voltage regulator to the right end of the circuit. Will this reduce the transmitting range? I guess yes.

Why C4 is different for different country? Because of the FM frequency of each country is different? It is 88MHz to 108MHz here.

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Of course it will and it will reduce the stability. The whole point of the regulator is to keep the supply to the oscillator constant so the frequency doesn't changhe as the batteries run down. C4 changes the premphasis which is different in Europe than the US, I don't know about Canada though I presume it's similar to the US.

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How if I'm not using battery but I convert AC to DC from the main socket? 5 volts supply to the whole circuit.

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Try the circuit with only 5V. The range will be much less, so it won't overload a cheap FM radio as much.

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Uncle $crooge

 

Do you mean I can't tune to it with a cheap radio if I reduce the supply voltage?

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A cheap FM radio gets overloaded when it is near a transmitter. When it is overloaded then it might not work. With a 5V supply, the transmitter's power is much less so a cheap radio might not be overloaded.

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Uncle $crooge

 

That depends on whether the mains adaptor's output current and whether it's regulated or not. If it's rated for a fairly high current and isn't regulated then you'll get about 8V with the transmitter connected. This is pretty similar to a 9V battery but you'll get loads of mains hum on the output because of the ripple (the filter capacitors are normally undersized).

Run it from a 9V mains adaptor using a 5V regulator for the oscillator section with a huge 100µf capacitor across the power supply rails.

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I designed the mic preamp for a 5V regulated supply. It won't work if the voltage is different.

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Okay, thanks. I'll try with 9 volts first.

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Sorry, I meant run the oscillator and pre-amp stages from a 5V regulator.

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I used a low-dropout regulator that still regulates very well with a 5.0V output when the battery voltage drops to 5.4V. An ordinary 7805 regulator doesn't regulate if its input voltage is less than about 7.5V.

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I wasn't talking about a battery, I was talking about a powerbrick.

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Hi,
I've almost completed putting the components together. It is around 10 x 3 cm.
Here are my questions:
I couldn't find a 160k (R2) resistor but I can get 150k. Can it be replaced?
Can I replace the 30k (R3) with a 33k resistor?
Or R2 and R3 need to be in ratio to provide the voltage devider?
What's the value should C4 be? Operating at 88 to 108MHz.
Can I replace the 30pF (C12) with a 22pF capacitor?
The turns of my coils is not touching to the neighbour turn exactly, just very near. Can this affect the operation?
I'm not using low drop-out voltage regulator but a 7805. I think it should be okay if I use a power supply with 9 volts? How if I use a 9 volts rechargeable battery? I don't think it last very long.
Is there any suggestion on cutting the metal on the veroboard to disconnect the connection? Usually i use penknife to cut, very troublesome and I don't like to do this.

Thanks

Attached Images

Mod4.GIF (12.3 KB, 32 views)

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It looks nice but is twice as long as mine.

160k and 30k are standard 5% values. The ratio must be close, use 180k for R2 and 33k for R3.

I don't know if FM radio stations in your country use pre-emphasis (treble boost) like in Europe or like in North America. Ask the engineer at a local FM station.

Yes.

My coils have enamel insulation and are made with the turns touching. If yours isn't insulated then the turns must not short together, but a space will change the inductance. Maybe it can still be tuned to an FM band frequency.

A 7805 regulator is fine if you use a 9V power supply. A Ni-Cad or Ni-MH rechargable "9V" battery is actually only 7.2V so cannot power some 7805 regulators. Its charge will power the transmitter with a low dropout regulator for about 1/2 hour to 1 hour. A 9V alkaline battery will power the transmitter with a low dropout regulator for about 6 hours.

I use a drill-press and sometimes just a drill bit held in my hand. A real Veroboard cutting tool is like a drill bit in a handle.

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