The main parts of this circuit is IC 7806,It is normal IC linear dc voltage regulator 6V at 1A current.
It is easy project electronic because used the minority part and low cost too.
I have of a 9Vac 1A transformer,The output of the transformer is rectified by diode 1N4001 or equivalent to more high power,
Thence to smoothed filter using 470uF 35V capacitors,so the volt this is unregulated DC voltage have value 11V-12V DC.
Besides must use this ic with a suitable heatsink.
Detail more,Please in image circuit.

The gain of U1 can be controlled by a digital binary 1248 nibble at ABC.
The gain at digital 000 is unity or 1 and the gain at various stages are set by 4051.
There are eight different gains as the steps of gain resistor network is chosen by 4051.
The on resistance of 4051 channel around 100E gets added to U1 pin 2 internal impedance.

You can use separate resistor networks with trimpots for each channel if you require
but keep the networks total burden on U1 pin 6 to around 10K, not less than than.
You can use this to set the gain of a amplifier with the help of a microcontroller.

Read more Source:
http://schematics.blogspot.com/2005/01/digital-gain-control-of-opamp.html
Thank you.

If you want used easy variable regulator power supply voltage 0-30V at current 1.5A max. I am like this circuit, because it is small but very good.
I uesd IC - LM317T it is quality products ic variable regulator,so i like make in other power circuit.
I made use of a 24Vac 1A transformer,The output of the transformer is rectified by diode 1N4002 or equiv ,and smoothed filter using 2200uF capacitors.
The float-voltage measured here for the 24V transformer was 34V-35V,it is unregulated DC voltage.
The VR1 is control output dc voltage 0V(1.25V) to 30V(32V) at 1.5A max all range.
.It’s advised that you use this ic with a suitable heatsink.

Main Part
- IC1 = IC LM317T or KIA317
D1-D4 = Diode 1N4002 or 1N4004 or 1N4007 x 4
C1 = Capacitors electroly 2,200uF 35V
VR1 = Variable Resistor 5K(B)
Other detail part,Please see in image.

LCD2USB is a open source/open hardware project. The goal of LCD2USB is to connect HD44780 based text LCD displays to various PCs via USB. LCD2USB was meant to be cheap and to be made of easily available parts. It is therefore based on the Atmel AVR Mega8 CPU and does not require any difficult to obtain parts like separate USB controllers and the like.

Read More source:
http://www.harbaum.org/till/lcd2usb/index.shtml
Thank you.

This is an easy to build stepper motor driver that will allow you to precisely control a unipolar stepper motor through your computer’s parallel port. With a stepper motor you can build a lot of interesting gadgets such as robots, elevator, PCB drilling mill, camera panning system, automatic fish feeder, etc. If you have never worked with stepper motors before you will surely have a lot of fun with this project.

Read More Source:
http://www.electronics-diy.com/stepper_motors.php
Thank you.

This is a constant current source using a FET. This is the most simple replacement to series resistor to limit current.

The N-Channel FET BF256C can give 15mA current.

Read More Source:
http://schematics.blogspot.com/2007/02/fet-current-source.html
Thank you.

The buuffer electronic with IC Opamps by CA3140 or LF353 or TL072.
If output impedance of a point is a high value then connecting another circuit at that point will load it resulting in malfunction or error. Buffers are used as interface between circuits. Low impedance of an output means it can source sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps. A non-inv FET input is the best buffer, for inverting buffer use high R values Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs. Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 79L05 for the dual supply required by this circuit.

Read more source:
http://schematics.blogspot.com/2004/10/buffer-opamps.html
Thank you.

I want mini size switching regulator,so it input voltage 9V to 3V Step-Down Converter circuit.
The LT1073 is good idea,it used for dc to dc converter.
if want it,please read in http://www.linear.com .
Vout 3V at 100mA, L1 100?H , D1 - Diode 1N5818 or equiv

Detail more,please in image.

This is a digital thermometer based on USB PIC16C745 from Microchip and DS1820 sensor from Dallas Semiconductor. Temperature readings are sent over USB port in HIDCOMM USB mode to VB6 program on a PC. Hex program and sample Visual Basic 6 application is included.

Read More Source:
http://milan.milanovic.org/skola/parport/usbport-05.htm
Thank you.

Why build my own USB to RS232 converter when there are adapters already available from many suppler? The Answer is simple: Neither the strand “USB to RS232 converter” actually worked *properly* with all the devices I tried. But, They did not seem to support ALL the RS232 lines. The USB to RS232 converter using the FT8U232AM and a Maxim-IC MAX235

Read more source:
http://www.pccompci.com/usb-converter/usb-converter.html
Thank you.