Audio Amplifier Circuit using STK083

Audio Amplifier Circuit using STK083

STK083 Audio Amplifier Circuit

Circuit diagram 500mW FM PLL transmitter 88-108MHz using LMX3206 – PIC16F870

Circuit diagram 500mW FM PLL transmitter 88-108MHz using LMX3206 – PIC16F870

Circuit diagram 500mW FM PLL transmitter 88-108MHz

500mW PLL FM transmitter 88-108MHz
This PLL transmitter is controlled and the frequency is very stable and can be programmed digitally.
Transmitter will work 88-108 MHz and output power up to 500mW.
With a small change can set the frequency of 50-150 MHz.

The output power is often set to several watts with transistors.
So therefore I decided to build a simple transmitter with great performances.
The frequency of this transmitter can easily be changed by software and space / compress air coil.
This transmitter is the oscillator colpitts. Oscillator is a VCO (voltage controlled oscillator) which is set by the PLL circuit and PIC micro controller.


This oscillator is called the Colpitts oscillator and voltage controlled to achieve the FM (frequency modulation) and PLL control. T1 must be HF transistors to work well, but in this case I use a cheap and common BC817 transistor. LC tank oscillator needs to oscillate properly.
In this case the LC tank consists of L1 with the C1, C2, C3, and varicap BB139.
Coil parallel to the C1 and C2 in series. The same with the varicap and C3.
You may think that L is parallel to the [(C1 / / C2) + (Varicap / / C3)]
C3 will determine the value range VCO. Large value of C3 will be broader in the range VCO can be.

PLL and Microcontroller


Oscillator is made to work as a “Voltage Controlled Oscillator” VCO.
To control the frequency synthesizer circuit LMX 2306 has been added. The PLL circuit has a pickup coil (L2) is connected to pin 6.
This coil should be placed close to the coil L1 to take some of the energy oscillates.
The LMX2306 PLL in to use this frequency to adjust and lock the VCO to the desired frequency.
Systems also need to set the external reference crystal. In this case I use 12.8 MHz.
 pin2 of MX2306 you will find the PLL filter to form a VM that is set voltage of the VCO.
The PLL tries to arrange so that the oscillator frequency Fout kept locked to the desired frequency.
The desired frequency programmed into the PIC EEPROM and clocked into the synthesizer (LMX2306) at power up.
I will below explain how to program the EEPROM to different frequencies.
In the pin14 of your synthesizer control output. In this output you will find a reference frequency for testing.

(I must warn you that the signal is not symmetrical in form. Pulsa positive only a few microseconds, so you will be hard to see on the oscilloscope.) I solved by connecting it to 74HC4020 (14-stage Binary Counter) to input pin 10 Hours. In Q0 (pin 9) you will have a symmetrical square wave with a frequency half since the circuit is a table. In Q1 pin 7 will be divided by 4, see data sheet for more information.

LF input
You want to send audio must be connected to the audio input (left schematic).
Will affect the signal and thus modulate the FM varicap RF carrier frequency.
A potentiometer P1 was added to adjust the depth of modulation (FM Wide or Narrow FM). You may have to play a bit with a value of P1 because it tends to modulate the lot. You may need to add the 500k – 1M potentiometer only. You test and find out for himself.

Buffer stage
Here you find other HF transistors and work in the class C.
Resistor R1 and resistor Re2 regulate the flow of DC. In this case I find that 9.1k will give a good output power and thus equal to 150. If you want to increase the power should be lower Re2. You can add another 150 ohm resistor in parallel.
In the table below I’ll show the output power with different voltages and resistor values of Re2.
I advice you to not run the transmitter with a high output power. Transistor I use is small and tends to be hot.
I advice you to run the unit from the 0 – to 200mW. At the transistor will 500mW pain …* smiles *
At the output you will find a network T. This “filter” will match the transmitter to the antenna impedance output stage.
You have two variables 60pF capacitors to tune the transmitter for best performance.
The antenna I use I a 1 / 4 wave whip antenna (wire) about 75cm long.
Smaller antenna types, but not so good performance as a dipole.
With a dipole you will be more long distance transmitter.
How long can I pass?
It is a very difficult question because the environment affects the transmission distance is very much.
In a city environment with concrete buildings transmitter will send maybe 200m.
I will send a proposed open 2000m.
I did the test and filed with 70mW output power into a “bad” whip antenna is placed in the room I can send 200-300m to a park without a problem.

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.
 
download

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