Derived Center-Channel Stereo System

A simple method of deriving a center or third channel without the use of an extra transformer or amplifier, (a) 4- speakers are connected to 8- amplifier taps. 8 and 16- speakers connect to 16- taps, (b) By blending the inputs it is possible to cancel out undesired crosstalk.

Derived Center-Channel Stereo System

Audio Filter Analyzer

When this circuit is connected to a filter and an oscilloscope, the scope displays the filter`s frequency response. Afrequency that sweeps from low to high is applied to a filter. An oscilloscope is triggered by* the start of the sweep and ends its trace at the highest frequency of the sweep. The filter output goes to the vertical amplifier of the oscilloscope. Using bandpass filters as an example, as the bandpass frequency is approached, reached, and passed, the scope follows the peaking output and draws the response curve. A neat effect! The 566 VCO (Ul) produces a VLF triangle wave to frequency modulate the next stage. It also produces a square wave to externally trigger the scope. Op amp U2 (a 741 unit) optimizes the amplitude and the dc component. Another VCO (U3) produces the actual sweeping triangle wave. Its frequency is selectable via SI. Op amp U4 (another 741 op amp) is set up as a bandpass filter and has been included as an example filter. Finally, diode D1 chops off the bottom half of the output, and leaves a nice bell curve. lb set up and operate, power-up the circuit and scope. Set the scope`s TIME/CM to 50 ms/cm. Set the VOLTS/CM control to 2 V. Attach a probe from the circuit`s trigger to the scope`s external trigger input. Set the triggering mode to normal, external. Attach a probe from the vertical amplifier to TP1. You`ll see a diagonal line that runs across the CRT. Input coupling should be set to dc. Adjust the triggering level until the diagonal runs from the upper left to the lower right of the CRT to ensure a displayed sweep from low to high. Now, disconnect the probe from TP1 and attach it to the filter output past the diode. via next.gr

Audio Filter Analyzer

Audio Filter Circuits

The circuit as shown gives the bandpass operation the transfer function calculated from FBP(s) = where = 1 + s/Qo>0 + s2/w02. The cut-off frequency, 0, and the Q-factor are given by 0 = g/C and Q = gR/2 where g is the transconductance at room temperature. Interchanging the capacitor C with the resistor R at the input of the circuit high-pass operation is obtained. A low-pass filter is obtained by applying two parallel connections ctf R and C as shown in Fig. 2. The low-pass operation may be much improved with the circuit as given in Fig. 3.

Audio Filter Circuits

Here the gain and Q may be set up separately with respect to the cut-off frequency according to the equations Q = 1/fB = 1 + R2/R!, A = Q2 and 0 = g ffi/C.

Programing UART in ARM Microcontrollers

A UART is usually an individual (or part of an) integrated circuit used for serial communications over a computer or peripheral device serial port. UARTs are now commonly included in microcontrollers. A dual UART, or DUART, combines two UARTs into a single chip. An octal UART or OCTART combines eight UARTs into one package, an example being the NXP SCC2698. Many modern ICs now come with a UART that can also communicate synchronously; these devices are calledUSARTs (universal synchronous/asynchronous receiver/transmitter).

Programing UART in ARM Microcontrollers: you can find here: www.gadgetronicx.com

Programming tutorial adc ARM Microcontrollers

So, the microcontrollers today offering a more and simple solution our lives. One of the controllores is LPC11Cx2. The LPC11Cx2/Cx4 are an ARM Cortex-M0 based, low-cost 32-bit MCU family, designed  for 8/16-bit microcontroller applications, offering performance, low power, simple instruction set and memory addressing together with reduced code size compared to existing 8/16-bit architectures.The LPC11Cx2/Cx4 operate at CPU frequencies of up to 50 MHz. The peripheral complement of the LPC11Cx2/Cx4 includes 16/32 kB of flash memory, 8 kB of data memory, one C_CAN controller, one Fast-mode Plus I2C-bus interface, one RS-485/EIA-485 UART, two SPI interfaces with SSP features, four general purpose counter/timers, a 10-bit ADC, and up to 40 general purpose I/O pins.On-chip C_CAN drivers and flash In-System Programming tools via C_CAN are included. In addition, the LPC11C22 and LPC11C24 parts include an on-chip, high-speed CAN transceiver. 

Programming tutorial adc ARM Microcontrollers

One of intereting article you can find here www.gadgetronicx.com 

Arduino Uno Rev3 schematic

arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf

Auto ranging ohmmeter using arduino

This article is about a simple auto ranging ohmmeter using arduino. The measured resistance is displayed using a 16×2 LCD display. The circuit is sufficiently accurate and uses minimum number of external components possible. Before going into the details of this project, lets have a look at the basic resistance measurement method.

Resistance measurement.

The figure above shows the circuit diagram of a simple resistance measurement scheme. Rx is the resistance to be measured. R1 is the input resistance. i is the current passing through the loop and 5V is the supply voltage. To find the unknown resistance Rx, the voltage across Rx is measured first. let the voltage across R1 be VR1. Then VR1=5-Vx. The current i=VR1/R1=(5-Vx)/R1. Since R1 and Rx are connected in series, the current through them will be equal. So the unknown resistance Rx= Vx/i. The voltage across the unknown resistance is measured using the ADC of the arduino. To be precise, analog channel A5.

Anyway this method have a drawback. If there is great difference between the input resistance and the Rx, the result will be extremely inaccurate. This is because almost all of the input voltage will drop across the larger resistance and this provides very less information.

Suppose R1=10K and Rx=100 ohm. Then the voltage across R1 will be 4.95v and voltage across Rx will be 50mV and this gives less information. The sensitivity of the arduino is 4.889mV. So when we read 50mV using the arduino ADC the result will be 10. When converted it into voltage the result will be 10 x 4.889mV =48.89mV. Then Rx= 0.0488/((5V-48.89mV)/10000) = 98.7 ohm.

Suppose R1=10 and Rx=220 ohm. Then the voltage across R1 will be 4.89V and voltage across Rx will be 107mV. The corresponding digital reading will be 21. When we convert it into voltage the result will be 21 x 4.889mV=102mv. Following the calculations used in the previous case, Rx=208 ohm. In the above two cases you can see accuracy issues. The most accurate result occurs when the Rx and R1 are as close as possible.

Auto ranging.

A scheme for estimating the value of Rx roughly and then putting a matching resistor in place of R1 is what we need here and this method is called auto ranging. The circuit given below demonstrates auto ranging. 

Resistances R1 to R7 are the input resistors. In this scheme the free end of one resistor is held high and the free ends of other resistors are held low. The the voltage across the unknown resistance Rx is measured. Diodes D1 to D7 are used to prevent the back flow of current towards the low ends. Suppose free end of R1 is held low. If R1 and Rx are equal, then the voltage drop across Rx will be (5-0.7)/2 = 2.15 where 0.7 is the diode drop. If the voltage across Rx is less than or equal to 2.15, we can assume that Rx is less than or equal to 220 ohms. The closest value possible for the input resistance is 220 ohms and so this loop is considered for calculation. If the above condition is not satisfied, the above steps are repeated with the succeeding input resistors until we get a solution.

Circuit diagram.

Full circuit diagram of the auto ranging ohmmeter using arduino is shown in the figure above. Digital pins 1, 6, 7, 8, 9, 10, 13 of the arduino are used to switch the input resistors R1, R2, R3, R4, R5, R6, R7 respectively. Resistors D1 to D7 are used to prevent the back flow of current through the corresponding path. D8 is the power ON indicator LED. POT R10 is used for contrast adjustment of the LCD. Resistor R9 limits the back light LED current.

Program.

#include<LiquidCrystal.h>
int vin=A5;
int t=1;
int u=6;
int v=7;
int w=8;
int x=9;
int y=10;
int z=13;

int at;
int au;
int av;
int aw;
int ax;
int ay;
int az;
int a;
double vx;
float rx;
double i;
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup()
{
pinMode(vin,INPUT);
lcd.begin(16,2);

pinMode(t,OUTPUT);
pinMode(u,OUTPUT);
pinMode(v,OUTPUT);
pinMode(w,OUTPUT);
pinMode(x,OUTPUT);
pinMode(y,OUTPUT);
pinMode(z,OUTPUT);

digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
}
void loop()
{

digitalWrite(t,HIGH);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
delay(100);
at=analogRead(vin);




digitalWrite(t,LOW);
digitalWrite(u,HIGH);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
delay(100);
au=analogRead(vin);
digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,HIGH);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
delay(100);
av=analogRead(vin);



digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,HIGH);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
delay(100);
aw=analogRead(vin);


digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,HIGH);
digitalWrite(y,LOW);
digitalWrite(z,LOW);
delay(100);
ax=analogRead(vin);


digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,HIGH);
digitalWrite(z,LOW);
delay(100);
ay=analogRead(vin);



digitalWrite(t,LOW);
digitalWrite(u,LOW);
digitalWrite(v,LOW);
digitalWrite(w,LOW);
digitalWrite(x,LOW);
digitalWrite(y,LOW);
digitalWrite(z,HIGH);
delay(100);
az=analogRead(vin);

if(az>=450)
{
vx=az*0.00489;
i=(5-vx-0.55)/22000;
rx=(vx/i);
}
if(ay>=450 && az<450)
{
vx=ay*0.00489;
i=(5-vx-0.55)/10000;
rx=(vx/i);
}
if(ax>=448 && ay<448 && az<448)
{
vx=ax*0.00489;
i=(5-vx-0.55)/4700;
rx=(vx/i);
}

if(aw>=439 && ax<439 && ay<439 && az<439)
{
vx=aw*0.00489;
i=(5-vx-0.55)/2200;
rx=(vx/i);
}

if(av>=439 && aw<439 && ax<439 && ay<439 && az<439)
{
vx=av*0.00489;
i=(4.8-vx-0.55)/1000;
rx=(vx/i);
}

if(au>=430 && av<430 && aw<430 && ax<430 && ay<430 && az<430)
{
vx=au*0.00489;
i=(4.5-vx-0.55)/560;
rx=(vx/i);
}

if(at>=430 && au<430 && av<430 && aw<430 && ax<430 && ay<430 && az<430 )
{
vx=at*0.00489;
i=(4.5-vx-0.55)/220;
rx=(vx/i);
}

if(at<430 && au<430 && av<430 && aw<430 && ax<430 && ay<430 && az<430 )
{
vx=at*0.00489;
i=(4.5-vx-0.55)/220;
rx=(vx/i);
}
lcd.setCursor(0,0);

if(vx>4.8)
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print("----INFINITY----");
}
else
{
if(rx<1000)
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print(rx);
lcd.setCursor(7,0);
lcd.print((char)244);
}
else
{
lcd.clear();
rx=rx/1000;
lcd.setCursor(0,0);
lcd.print(rx);
lcd.setCursor(6,0);
lcd.print("k");
lcd.print((char)244);
}
}
lcd.setCursor(0,1);
lcd.print("Arduino Ohmmeter");
}

sourse: www.circuitstoday.com