Understanding FM transmitter circuit

Understanding FM transmitter circuit

Hi,


I'm trying to understand how the following FM transmitter circuit works. I got it from the site

Wireless FM Transmitter. The site has some explanation on how the circuit works, however I'm not sure about a few things, including the electret mic & how the frequency modulation takes place.

The electret microphone has a current of 200uA which changes by +- 3 uA depending on sound waves. This sets the voltage across R1 to 2V and the voltage across the mic to 4 volts. As the sound hits the mic the current through R1 increases slightly reducing the voltage across the mic. Is that what is happening?

This changing voltage is passed on by the coupling cap, C1 to the base of the transistor, which is biased by R2 & R3 to approx 2V. The voltage across R4 with no signal on the mic will be Vb - 0.7 (drop across vbe), 1.3 volts. As the voltage at b changes R4 will change by the same amount. This change in voltage is seen at the base of the tank circuit. And the signals voltage is increased/decreased. Isn't this what happens in AM? As wouldn't the capacitance need to change in order to get Frequency modulation? And if it was amplitude modulation occuring in the FM spectrum, then how would a radio receiver be able to demodulate the signal?

At this point I'm not sure what is happening at the capacitor C3, what is that doing? Is it holding CE at a fixed voltage? And is it along with capacitor C2 considered a bypass capacitor? Or do bypass capacitors need to be connected to ground?

2×25W Stereo Power Amplifier with STK4141II

2×25W Stereo Power Amplifier with STK4141II

Here the stereo power amplifier based on single IC STK4141II. This amplifier circuit will deliver 25W on each output channel.
Recommended voltage is 27.5V for 8ohms speaker and 24.5V for 4ohms speaker while the maximum voltage to supply this circuit should be about 41 VDC.

Heatsink usage on the power IC is a must.

Use this STK4141II Datasheet for your reference.
 
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Electric Niccan leaf car

New electric Car from Nissan named Nissan leaf . powered by 100 electric source

Classic deviled eggs recipe

Tecipe to create Classic deviled eggs recipe, perfect for post-Easter and summer picnic potlucks. Mashed cooked egg yolks, mixed with mayonnaise and Dijon, spooned or piped

vga pinout

vga pinout

vga pinout

1 - red out                                   6 - red return (ground)
2 - green out                                 7 - green return (ground)
3 - blue out                                  8 - blue return (ground)
4 - unused                                    9 - no pin
5 - ground                                    10 - sync return (ground)

11 - Monitor ID Bit 0

12 - monitor id 1 in or data from display

13 -horizontal sync out

14 - vertical sync

15 - monitor id 3 in or data clock

1.5V LED FLASHER CIRCUIT

1.5V LED FLASHER CIRCUIT

1.5V LED FLASHER CIRCUIT

AVERAGE CURRENT = 120uA

PEAK LED CURRENT = 20mA

4mS PULSE  1 FLASHE/SEC

APPROX. 6 MONTHS OPPERATION FROM N-CELL

APPROX. 12 MONTHS OPPERATION FROM AA CELL

DAVID JOHNSON AND ASSOCIATES

MINIATURE LED FLASHING CIRCUIT

1.5 VOLT CIRCUIT

lm3909 led flasher

lm3909 led flasher

LM3909 LED Flasher Oscillator

General Description

The LM3909 is a monolithic oscillator specifically designedto flash Light Emitting Diodes By using the timing capacitor

for voltage boost it delivers pulses of 2 or more volts to the LED while operating on a supply of 1 5V or less The circuit is inherently self-starting and requires addition of only a battery and capacitor to function as an LED flasher

Packaged in an 8-lead plastic mini-DIP the LM3909 will operate over the extended consumer temperature range of b25 C to a70 C It has been optimized for low power drain and operation from weak batteries so that continuous operation life exceeds that expected from battery rating

Application is made simple by inclusion of internal timing resistors and an internal LED current limit resistor As shown in the first two application circuits the timing resistors supplied are optimized for nominal flashing rates and minimum power drain at 1 5V and 3V

Timing capacitors will generally be of the electrolytic type and a small 3V rated part will be suitable for any LED flasher

using a supply up to 6V However when picking flash rates it should be remembered that some electrolytics have very broad capacitance tolerances for example b20% to a100%

Features


Y Operation over one year from one C size flashlight cell

Y Bright high current LED pulse

Y Minimum external parts

Y Low cost

Y Low voltage operation from just over 1V to 5V

Y Low current drain averages under 0 5 mA during
battery life

Y Powerful as an oscillator directly drives an 8X speaker

Y Wide temperature range

Applications

Y Finding flashlights in the dark or locating boat mooring
floats

Y Sales and advertising gimmicks

Y Emergency locators for instance on fire extinguishers

Y Toys and novelties

Y Electronic applications such as trigger and sawtooth
generators

Y Siren for toy fire engine (combined oscillator speaker driver)

Y Warning indicators powered by 1 4V to 200V