Category Archives: Component

Op-Amps or Operational Amplifiers

741 Op-Amp Self assemble kit

741 Kit at Amazon

The “XL741” Discrete Operational Amplifier kit from Evil Mad Scientist Laboratories is a faithful and functional transistor-scale replica of the muA741 op-amp integrated circuit, the classic and ubiquitous analog workhorse. An Operational Amplifier, or “op-amp” as they are commonly known, is one of the most useful and common types of analog electronic circuit building blocks and the XL741 kit was designed by Eric Schlaepfer, in collaboration with Evil Mad Scientist Laboratories is lovingly designed to resemble one. The XL741 kit is sold as an easy-to-build soldering kit. It includes the circuit board, resistors, transistors and capacitor that make up the electrical circuit as well as printed assembly instructions. The kit also comes complete with the “IC Leg” stand, and 8 color coded thumbscrew terminal posts. Basic electronic soldering skills are required, but no additional knowledge of electronics is presumed or required and it should take about an hour to build. The XL741 circuit is a direct implementation of the “equivalent circuit” from the original Fairchild muA741 datasheet. It comes with terminal posts and solder points so that you can actually connect to it and build up classic and functional op-amp circuits.

Op-Amps or Operational Amplifiers

A operational amplifier has two inputs an inverting input that is 180 degrease out of phase of the output and a non-inverting input that is in-phase with the output. An op-Amps input impedance is very high. Buy Operational amplifiers

List of common Op-amps:

LM324 (quad opamp):

LM324 opamp

Low Power Quad Operational Amplifier
The LM324 can operate on a single voltage power supply. this op-amp has 4 independent operational amplifiers in a single chip.


LM741 opamp

The 741 op-amp is a common general purpose Operational amplifier.
This op-amp is useful as it has short circuit protection and high gain over a wide voltage( up to 18V max).


LM308 opamp

This opamp is now obsolete
the LM308 was a precision operational amplifier. It had a wide voltage range up to 18V and could run off an unregulated power supply.


LM386 opamp

The LM386 Operational amplifier is a Low voltage Audio Power amplifier and is some times refered to as a “audio op amp”. it also has a wide voltage range from 4V-12V or 5v to 18V Low distortion and Low current drain. This op amp was designed to be used as a low voltage product to be used in consumer products the Gain is set internally 20 20 to keep external components to a minimum, lowering product costs. The LM386 is an ideal product for basic audio circuits.

Good reads:

Op-amps and Linear Integrated Circuits – by Ram Gayakwad Op-Amp Circuits Manual: Including OTA Circuits – by R. M. Marston Operational Amplifiers (EDN Series for Design Engineers) – by G.B. Clayton and Steve Winder Operational Amplifiers: Theory and Design – by Johan Huijsing Operational Amplifier Noise: Techniques and Tips for Analyzing and Reducing Noise – by Art Kay




Types of OP amp Circuits:


opamp comparator

A Voltage comparator will determine witch voltage is greater, the result is the outputvoltage. If the non-inverting input(+) is greater than the inverting input(-) then theoutput voltage will be positive from the op-amps positive supply.

Inverting amplifier:

opamp inverting amplifier

In this configuration the Input signal is connected to the Inverting input on the Op-amp and the output is fed back 180 degrees out of phase into the inverting input(negative feedback) this reduces the gain of the amplifier. If Rf = Rin then the gain will be -1 and the op-amp will act as a simple inverter. The input impedance(z) is relatively low and is determined by Rin.

Non-inverting amplifier:

opamp Non inverting amplifier

In a Non-Inverting Op-Amp Input signal is used as a reference voltage on the non-inverting input of the op-amp. and the inverted input is basically referenced to ground. This circuit has a very High impedance(z) somewhere between 1M to 1T ohms.

Differential amplifier:

opamp Differential amplifier

Vout = (V2-V1)(Gain)

A differential amplifier will determine the difference between two input voltages andoutput the amplified difference that is determined by the external resisters in the circuit. If all the resisters are equal then the Gain will = 1. To adjust the gain you will need to change the Resistance of both the input voltage dividers equelly.

Voltage follower:

opamp voltage follower

Vout = Vin

An opamp voltage follower has a very useful characteristic as the input Impedance is extremely high and in-essence will isolate the input signal voltage from the outputsignal. this will reduce the loading effect on the signal source.

Schmitt trigger(“thermionic trigger):

opamp Schmitt trigger

Comparator implementation of a schmit trigger using positive feedback loop.

Inverted Schmitt trigger

Inverted Schmitt trigger.png

Non-Inverted Schmitt trigger

non Inverted Schmitt trigger



  • BasicStamp range from parallax inc.
  • The 16F84 from Microchip
  • The Atmega128 from Atmel

Micro-Controller are very important to modern electronics they replace hundreds of discreet logic chips with a single IC. A modern micro-controller has:
Flash ROM for the machine code that constitutes the program that will be run.
Ram that will be used for user variables at execution time.
EEPROM data area for storing non-volatile user data during execution time
Programmable trimmers for use internally at watch dog timers and other counters like the program counter that tells the micro-controller where it is in the program being executed
IO-ports to communicate to the outside world.
And of course the core that will include the ALU (Arithmetic Logic Unit) where most of the magic is done.


16F84 Pic Micro Controller

This is a PIC Micro-Controller (Programmable Integrated Circuit)
This IC is old and there are a lot of other new versions available that can do lots more, and use a lot fewer external components.

One of my first micro-controllers was the 16F84 and I still use these from time to time. They are great chips and are relatively easy to program and inexpensive. There are many nowadays that use less external components like the 16F88 that can run without an external crystal oscillator.
PIC micro-controllers are not humans they are machines, and machines can not understand human language to programme a PIC you will use assembly language which is mnemonic codes for machine code that they understand.
For example on a 16F84 which has 14bit OpCodes:
ADDLW (8 bit value to be added),(destination: 0 = store in working register//1=store in file) This means add a literal value to the working register.

In other words this means that the initial value in the working register (which is a storage place for a byte of information that the CPU is currently working with) will be added to a user supplied byte value and then stored back in the working register.

So therefore
in machine code:
11111x is the code for ADDLW
and 00000101 is the binary value for decimal 5
x is ignored
so the 14bit opcode is

As this can be difficult for most new comers to micro-controllers there are packages available to program PICS in higher programming languages like C which can be easier for some things but I much prefer to work in assembly myself.
Also to program the PIC you will need a programming board to transfer your code from your PC to the actual microchip that will do the work I build one many years ago that worked for years until I decided to buy a nicer looking one from Maplin electronics.

Velleman k8048 PIC Programmer

Velleman k8048 PIC Programmer

The Velleman k8048 PIC Programmer and experiment board: this is a nice piece of kit and can program many PIC ic’s as-well as having a ICSP interface to program other models that are not natively supported by the board

Buy from these suppliers in the UK:

Interpreted Language Microcontroller: Basic stamp

You can even get Basic interpreters preloaded on to PICS so you can program in a much simpler way that reads more like human language On. A good type of micro-controller that uses this is a Basic stamp

Basic Stamp 2 Discovery Kit

Flashing LED example for BasicStamp2:

DIR0=1 ‘ make Port 0 outputs
OUT0=1 ‘ turn on the LED
PAUSE 500 ‘ pause 500 milliseconds
OUT0=0 ‘ turn off the LED
PAUSE 500 ‘ pause 500 milliseconds
GOTO Begin ‘ Repeat this until the end of time.

As you can see this reads more naturally and is easy to see what is going on. The basicStamp can easily be programmed through a RS-232 port of a PC.


original arduino

Arduino is kind of a open-source version of the Basic Stamp it is programmed in the Arduino programming language, “Wiring” an open source Programming language based for micro controllers you can download the latest version from:

Buy from these suppliers:


AT90USBKEY board

AT90USBKEY demonstration board from Atmel uses a AT90USB1287 micro-controller this is a very nice and simple micro-controller as it uses a USB interface and is becoming very popular. It has the following features:

  • USB-OTG support
  • 16 MB of DataFlash,
  • LEDs
  • a small joystick
  • temperature sensor (thermistor).
  • clocked at 8 MHz with the onboard crystal
  • comes with software which lets it act as a USB Mass Storage device
  • It’s operated from an external power source battery, mains or USB

Buy the AT90USBKEY from these international suppliers:

Teensy USB Development Board

teensy board

The Teensy is a complete USB-based microcontoller development system, in a very small footprint! All programming is done via the USB port. No special programmer is needed, only a standard “Mini-B” USB cable and a PC or Macintosh with a USB port. Features:

  • USB can be any type of device
  • AVR processor, 16 MHz
  • Single pushbutton programming
  • Easy to use Teensy Loader application
  • Free software development tools
  • Works with Mac OS X, Linux & Windows
  • Tiny size, perfect for many projects
  • Available with pins for solderless breadboard
  • Very low cost & low cost shipping options

7400 Quad 2 input Nand gate

7400 ic ANSI Symbol
ICE Symbol
Boolean equation: y= AB
The 7400 consists of 4 (quad) inverted AND gates(Nand) this is the compliment of the output of a regular AND gate. In boolean algebra any Boolean equation can be represented with Nand gates alone.


Electronics for Dummies – UK Edition (Paperback) by Dickon Ross, Cathleen Shamieh & Gordon McComb

It’s a Low-power Schottky family which uses fast Transistor-Transistor Logic (TTL) but requires more power than later families. However later Ic’s are still called TTL even though they do not use TTL anymore. It uses a supply voltage of 5V �0.25V and should be smoothed with small capacitors in the range of 0.033uF to 0.1uF linked directly over the supply pins as close to the IC as possible to remove power spikes caused by the switching circuits inside the IC itself. all unused pins should be connected to Vcc (+V) to insure that the IC does not pick up ambient noise. The outputof a 74LS can drive up to 10 other 74LS IC inputs but if more inputs need to be driven you should either use a transistor or a BUS-Driver IC. The output can only source +/- 2mA and should use a transistor to drive larger outputs,it can however sink up to 16mA of current and can light a LED which needs 10mA to emit light directly in the inverted state. The time taken to travel through a Gate state is about 10nS and can run at about 25MHz.


uses CMOS logic with the low power consumption of 4000 series IC’s and the high speed of TTL. They have the same pin arrangements as the older 74LS family however the 74HC inputs cannot be driven by 74LS outputs as there low voltage range is not compatible and you should use the 74HCT instead with 74LS compatible inputs. The Inputs have very high impedance and will not affect the circuit they are connected to however this also means that any unconnected input will switch between a high and a low state very rapidly causing an increase in supply current and the ic to behave undesirably. This IC needs a supply voltage of 2 to 6V and is tolerable to voltage spikes. The outputs can both sink and source about 4mA and you should again use either a transistor or a BUS-Driver to switch larger circuits. the output can drive many inputs of 74HC class IC’s quite easily. this IC also has a switching time of about 10nS.


like the 74HC it has high speed TTL and low power consumption of CMOS. The 74HCT can be safely used in the same circuit as 74LS this means it can be used as a direct low power replacements for the older 74LS series. The only problem is that the 74HCT has a lower immunity to noise, but this usually is not a problem in most systems. The Ic needs a supply of 4.5V to 5.5V so its best to use a smoothing circuit for the supply voltage. both the 74HC and 74HCT series IC’s are static sensitive. Touching a pin while your body holds a charge can damage the IC. most common IC’s are quite tolerant but it is advisable to discharge yourself with an anti-static wrist strap connected to earth or ground yourself quite regally by touching something metal that is earthed before handling them. ICs should be stored in protective packaging until you are ready to use them. if you are designing a new circuit you should use the 74HC family.

List of other NAND gates:

7430: 8 Input NAND Gate

74133: 13-Input NAND gate

74134: 12-Input NAND gate with Three-state Output

7413: Dual Schmitt trigger 4-input NAND gate
7420: Dual 4-input NAND gate
7422: Dual 4-Input NAND gate with open collector outputs
7440: Dual 4-input NAND Buffer
74140: Dual 4-input NAND Line Driver

7410: Triple 3-input NAND gate
7412: Triple 3-input NAND gate with open collector outputs

7400 Quad 2-input NAND gate
7401 Quad 2-input NAND gate with open collector outputs
7403: Quad 2-input NAND gate with open collector outputs (different pinout than 7401)
7424: Quad 2-input NAND gate gates with schmitt-trigger line-receiver inputs.
7426: Quad 2-input NAND gate with 15V open collector outputs
7437: Quad 2-input NAND Buffer
7438: Quad 2-input NAND Buffer with open collector outputs
7439 Quad 2-input NAND Buffer
74132: Quad 2-input NAND Schmitt trigger
74804: Hex 2-input NAND Drivers

4011 – Buffered Quad 2-Input NAND gate
4012 – Dual 4-input NAND gate
4023 – Triple 3-input NAND
4044 – Quad NAND R/S ((tristate) outputs)
4068 – 8-input NAND gate
4093 – Quad 2-input Schmitt trigger NAND gate
4572 – Hex gate : quad NOT, single NAND, single NOR
40107 – dual 2-input NAND buffer/driver