Author Archives: opampbrain


Yes, it somewhat looks a spider with 6 legs (:P) and I believe it scares the real spiders and even bugs LOL.

Update: 17-01-2018

spider pic 003

design drawing, yes it’s not perfect and please excuse for this.  spider idea

spider pic cons1

A small hexapod with copper legs and HS-311 actuators/servo’s, I have used 3mm thick copper wire for legs, I had no better option at the of making So I did go with the things I have and a sheild wire, copper wire and paper tape to attach the 3 servo’s

spider pic cons2

With bending tools I was able to mould legs like and fix them to the motors.spider cons4

spider pic cons3

Yes It may not look good.  Soon the spider hits the floor and the spider is still in progress.


  1. power Source: 3.7V,2600mAh
  2. CPU: ATmega48 clocked 1.536MHz
  3. Actuators/servos: HS311
  4. Sensors: yet to be added
  5. Programming: AVR C
  6. Environments: indoor

and many thanks to the Sir protowrxs.

Little update: 17th january of 2018

Modifed the legs style looks perfect and walking is also good.

spider pic 006

spider pic 003

spider pic 004

spider pic 005

spider walking. 😛

I will add sensors to it and will update as soon as possible. Thank you all.




Class A MOSFET amplifier

I always enjoy building audio amp’s particularly Class A topology.

PCB’s of class A MOSFET amp


pic c a .png

pic c a 2.png

pic c a 1.png

PCB’s of class A MOSFET amp.

PCB class A .jpg

assembled class A amp board.jpg


irfp250n mosfet.JPG


power amp ca .JPG


I used two MOSFET’s  (IRFP250N) one is configured as current source and the other one is to amplify the signal, for the input stage I have used JFET 2SK209 provides high input impedance and the

output impedance of the amplifier is 2.6ohm’s

output of the amp is 5watts at 3% THD and each MOSFET dissipates 9.6watts of power efficiency of the amp is 26.04%


12AX7 Amplifier

I always wanted to build vacuum tube or valve amplifier. finally I made one hybrid amp.  just combined both valve and solid state.  For the preamp section I have used 12ax7(dual triode) and for the solid state I built opamp based power amp configured in unity gain..

This is the low power version and I’m sure I am going to build medium power amp delivers atleast 5-10watts to the speaker and no solid state 😀

Here is the picture of my construction:



Audio Exciter amplifier

Audio exciter:

Exciter is also known as bodyshaker, Audio Exciter is  just basically a loud speaker without a membrane, and it consists of voice  coil , oscillating mass and mounting ring/plate.  If the audio/music signal is applied to the contact pins of the voice coil, the oscillating mass starts shaking with the frequency of the applied music, the oscillation is transmitted to the mounting ring and from there on  to the surface the exciter sticks to, thus the excited surface emits the music signal.

audio exciter

audio exciter2

For testing the audio exciter I did built a small opamp based amplifier which delivers 2Watts rms at 6ohms impedance amplifier exciter

This amplifier circuit is nothing new. and you can find a better one here  (discrete transistor amp)

LED candle avr

This is a simple project, called  LED candle. I will be using yellow LED’s of 2 and a simple PWM code that runs on AVR (ATmega328p) chip make’s the LED flickering that almost looks like candle.  😛  for candle I will be using  LED’s+translucent paper.

two-yellow-leds       translucent-paper



LED candle





code is very straight , Simple PWM code runs on ATmega48/328p

#define F_CPU 1000000UL
#include avr/io.h
#include util/delay.h

#include avr/interrupt.h

void timer1_init(void);

void timer1_init()
DDRB |= 1<<PINB1; //
DDRB |= 1<<PINB2;

TCCR1A |= 1<<COM1A1 | 1<<WGM11; //
TCCR1A |= 1<<COM1B1;
TCCR1B |= 1<<WGM12 | 1<<WGM13 | 1<<CS10; //
ICR1 = 49; //top value

int main(void)

OCR1B = rand() % 47 + 1;

OCR1A = rand() % 47 + 1;




LM4752 amplifier

LM4752 is a stereo audio amplifier capable of delivering 11watt per channel of continuous average output power to a 4Ω load, or 7W per channel into 8Ω, using a single supply at 10% THD+N.  A simple mute function can be implemented with the addition of a few external components.

LM4752 circuit

lm4752s amp pic1

lm4752s amp pic2


pictures of my old projects.

Old projects.


Mini tank robot was my one of oldest project. I built it for fun, no use only for fun.  I did used ADXL335 accelerometer for inclination detection , AVR microncontroller (ATmega164P) for processing and controlling  and L293D motor driver Chip and BO series motor.



robot 2


POV display based on ATmega48


lm4752s amp pic1    lm4752s amp pic2






Robot project

master-slave robot arm  or teleoperator, this is one of my oldest project which I was built in 2012, For this simple application I did used NE556 IC to control Servo motors,  It is a dual timer chip and yep brother of very famous chip called NE555,  NE556 dual timer chip, one timer  configured in astable mode and output of it is connected to another timer which is configured in monostable and the pulse width is controlled by simple potentiometer or variable resistor which is connected in monostable circuit(RC network), Monostable output is a control signal further conneted to control terminal of analogue servo motor.

Master_arm (potentiometers as position sensors)  wooden arm

master arm

master arm(potentiometers as position sensors)

Slave_arm with cheap servos

slave arm

slave_arm with servo’s

Control circuit using NE556 dual timer chip and some other passive components

control circuit

master slave robot arm


KA7500C application circuit

This buck converter/step down circuit is based on KA7500c SMPS controller chip,
the following circuit is from the reference design you can find the details of the circuit and calculations from the document. This is one of the application circuit built around with KA7500C, this buck converter  can suply a load current of 5.75Ampere at 5V we could also use  TL494 or KA7500c both are same in operation/ratings. The recommended operating voltage range is 7V to 40V DC and the power source i am using for this is a old laptop power supply adapter rated 18V,3.7A. , however the maximum input current the circuit draws is 2A at full load.

circuit diagram:

ka7500c circuit buck converter

ka7500 application circuit buck


KA7500 buck converter


KA7500 buck converter_1

buck converter can supply load current of 5.75A at 5V and the short circuit current is 7Ampere.  the maximum output is 5V×5.75A, the ripple voltage at max power out is 94mV and input power is 18V×2A and the efficiency(η) calculated

η = output power/input power = 5×5.75/18×2
η = 79.86%

Note: C1,C2,C3 are the low ESR electrolytic capacitors add 2 of 100nF,50V rated ceramic capacitors in parallel to C1,C2,C3, to reduce the high frequency noise.

L1,  FS-1RN series toroidal cores made from iron powder (26) for creating inductors, FS-1RN core or similar  you can get this one from old desktop PSU’s. here is a useful link of toroids,  one of my friend Mr William helped me in selecting toroidal core, thanks to him.

Q1 , Q2  are2SB772 2SC4468 they are audio transistors, can be  used for switching applications, linear.