Introduction: LM741 Op Amp on a Breadboard

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About: Jack passed away May 20, 2018 after a long battle with cancer. His Instructables site will be kept active and questions will be answered by our son-in-law, Terry Pilling. Most of Jack's instructables are tuto…

This is an LM741 op-amp built on a breadboard. The LM741 op-amp is an 8 pin IC chip, but I thought it would be fun to build my own on a breadboard. There are four sections to the chip, it will be built on four Adafruit Perma Proto boards. The design is from an open source kit from Evil Mad Scientist Laboratories. Their product page which includes additional information about the 741, and a datasheet with a schematic, is located here.

To build it you will need:

  • 1 - Wood base 3.5 by 11 by .75 inches thick
  • 4 - 1/2 Size Breadboard PCB https://www.adafruit.com/products/1609
  • 8 - #6x3/4 Wood screws *
  • 8 - #6x1/4 Nylon spacers *
  • 1 - #6 Fibre washer *
  • 13 - 2N3904 NPN Transistor part #2N3904FS-ND **
  • 7 - 2N3906 PNP Transistor part #2N3906-APCT-ND **
  • 2 - 1 kΩ 1/4 Watt resistor part #CF14JT1K00CT-ND **
  • 2 - 51 kΩ 1/4 Watt resistor part #CF14JT51K0CT-ND **
  • 2 - 4.7 kΩ 1/4 Watt resistor part #CF14JT4K70CT-ND **
  • 1 - 39 kΩ 1/4 Watt resistor part #CF14JT39K0CT-ND **
  • 1 - 7.5 kΩ 1/4 Watt resistor part #CF14JT7K50CT-ND **
  • 1 - 24 Ω 1/4 Watt resistor part #24QBK-ND **
  • 2 - 51 Ω 1/4 Watt resistor part #CF14JT51R0CT-ND **
  • 1 - 33 pF ceramic capacitor part #BC1007CT-ND **
  • 2 - BAT85 Schottky diode part #568-11747-1-ND **
  • Female headers https://www.adafruit.com/products/2672
  • 22 gauge hookup wire (various colors)
  • DC Barrel Jack http://www.adafruit.com/products/373
  • 9 Volt battery

  • 9V battery clip http://www.adafruit.com/product/80

These items are needed only for assembly:

It occurred to me that it would be possible to make a mistake wiring something to it and damage it. So I included a fixture to test a circuit before plugging it into the board and a modular circuit for testing. If there is a wiring mistake in your circuit you can blow up a 66 cent 741 and save damage to your project.

Parts for the test fixture:

The modular circuit for testing uses a photocell to make a light/dark detector using these parts:

* Purchased locally at Ace hardware.

** http://www.digikey.com search for part number.

*** One breadboard needs to be half or full size, a small one will work for the second one. The breadboards and long male headers are used for making temporary fixtures to hold the female headers while soldering them.

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This is the second in a series of Instructables for IC chips built on a breadboard. The first was a 555 timer chip. The next one will be an LM386 audio amplifier. That won't be done for a while, it is in the early planning stages.

Step 1: The Base

I made my base out of a piece of scrap wood 3.5 by 11 by .75 inches thick.

Measure in 1.75 inches from one end and draw a vertical line.

Place one of the empty Perma-Proto boards so the line is visible through the mounting holes and centered vertically, and mark the location of the holes for the first board.

Mark the location of holes 2 1/2 inches to the left of the locations you just marked for the second board.

Mark the location of holes 2 1/2 inches to the left of the locations you just marked for the third board, and again for the forth board.

Drill a 1/16 inch hole 1/2 inch deep At each of the eight locations you marked.

Step 2: Soldering the Female Headers on the First Board

The hardest part of the build is soldering the female headers for the wires that connect the different boards together.

The first board to build is the Differential Amplifier board. For this board, and all the others, row number one is on the top.

Cut two pieces with two connectors off of the female headers. You will lose one connector with each cut. Sand the ends smooth.

You need two breadboards to position the headers because the spacing of the power rails is different between a regular breadboard and the Perma Proto boards.

Place two male headers with two pins each spaced the same as the power rails on the Permo Proto board on the first breadboard like in the first photo.

Place a male header on the second breadboard with a female header on top of it. This is just to hold up the other end of the Perma Proto board, do not solder it.

Place the two, two pin female headers on the male headers.

The second photo shows the Perma Proto board placed upside down on the two breadboards.

Solder the two pin header on the left side of the board. The other two pin header is just there for balance, do not solder it.

The third photo shows the positioning for the rest of the headers.

Place a 2 pin male header in the breadboard in holes A13-14 with a female header on top of it.

Place one pin male headers with female headers on top of them at locations A4, A7, A21, J7, and J21.

Carefully place the board upside down on the headers making sure they are in the correct holes. When the board is turned over the headers in the breadboard in row J will be in row A on your finished piece. Solder the rest of the headers as shown in the diagram. Follow this same procedure when soldering the headers on the rest of the boards. The diagrams of each of the boards will show the proper location for the headers.

Step 3: Differential Amplifier

I found it worked best for to solder the headers, then the wires, then the resistors, other components, finally the transistors on each of the four boards.

Solder the wires and the components as illustrated in the photo and diagram.

The resistor between E19 and E22 is a 51 kΩ, notice the yellow wire and this resistor are both soldered into the same hole at E19. The color bands in the diagram are wrong because Fritzing does not have a 51 kΩ resistor.

The resistors at B21 - B25, and I21 - I25 are each 1 kΩ.

The PNP transistors (2N3906) are marked with a "P" in the diagram. They are always mounted with the flat pointing to the left.

The NPN transistors (2N3904) are marked with a "N" in the diagram. They are always mounted with the flat pointing to the right.

Mount the Differential Amplifier board on the left side of the base with the power connector on the top. One of the 1/4 inch nylon spacers goes under each screw.

Step 4: Bias Gererator

Build the circuit according to the diagrams.

Follow the same procedure as on the first board:

  • Headers
  • Wires
  • Resistors
  • Transistors

The resistor between C19 and C23 is a 4.7 kΩ.

The resistor between F11 and F15 is a 39 kΩ. The color bands in the diagram are wrong because Fritzing does not have that value. You will notice that I used a blue bodied 1% tolerance resistor. That was just because it was what I had on hand, a +/-5% will work just fine.

Mount the bias generator board next to the differential amp.

Cut a red and a black wire about two inches long and connect the power rails.

Cut two yellow wires about 2 1/2 inches long and connect J4 on the differential amp to A5 on the bias generator, and J13 on the differential amp to A13 on the bias generator.

Step 5: Gain Stage

Build the circuit according to the photo and diagram.

Follow the same procedure as on the first board:

  • Headers
  • Wires
  • Resistors and capacitor
  • Transistors

The resistor from G7-G11 is a 4.7 kΩ.

Due to Fritzing having a limited choice of resistor values all the rest of the resistors on this board do not have the right color bands in the diagram.

The resistor between F11 an F15 is 7.5 kΩ.

The resistor between I22 and the ground rail is 51 kΩ. A wire goes into the same hole as the resistor in I22.

The resistor between I23 and the ground rail is 51 Ω.

The 33 pF ceramic disc capacitor goes between B7 and B9.

Mount the gain stage board next to the bias generator.

Cut a red and a black wire about two inches long and connect the power rails.

Cut a green wire about 2 1/2 inches long and connect J5 on the bias generator to A4 on the gain stage.

Cut a yellow wire about six inches long and connect J14 on the differential amp to A17 on the gain stage.

Step 6: Output Stage

Build the circuit according to the photo and diagram.

Follow the same procedure as on the first board:

  • Headers
  • Wires
  • Resistors
  • Barrel Jack
  • Transistors

Make sure you leave the yellow wires between D1-G1, and D2-G2 a little long to so they don't interfere with the mounting screw.

Both resistors shown in the diagram do not have the right color bands, Fritzing has a limited selection of resistor values.

The resistor between I12 and I16 is a 24 Ω.

The resistor between J16 and J20 is a 51 Ω.

Cut off the side pin on the barrel jack and solder the back (+) lead into hole J28 then solder the other pin into J30.

Cut a red and a black wire about two inches long and connect the power rails.

Mount the output stage board next to the gain stage board. Place the fiber washer under the head of the screw by the eight pin headers. This is the only place where you need to worry about the screw head causing a short. The last picture shows the detail of the screw and the fibre washer.

Cut two white wires about 2 1/2 inches long.

Connect J7 on the gain stage to A10 on the output stage.

Connect J15 on the gain stage to A21 on the output stage.

Cut a yellow wire about ten inches long and connect A7 on the differential amplifier to A3 on the output stage.

Cut a yellow wire about eight inches long and connect J7 on the differential amplifier to A2 on the output stage.

Pins one and five on the LM741 chip are the offset pins, rarely (if ever) used. There are female headers to connect them if you want to but they are optional. The newer dual op-amp chips don't even include the offset pins.

Step 7: Test Fixture

This is a fixture to test a circuit before plugging it into the board. If there is a wiring mistake in your circuit you can blow up a 66 cent 741 and save damage to your project.

The number 741 soldered into the upper right corner is there to distinguish this from a very similar piece I have. This is optional.

Very easy, just build it according to the photo and diagram.

Step 8: Light/Dark Detector, a Circuit for Testing

This is a modular circuit you can use to test your project.

The eight pin header is a male header with the pins pointing down.

The blue and orange wires are jumper wires, switching them in the two pin female header will change the circuit from a light to a dark detector.

The green LED is on when the output pin is high and the red LED is on when it is low.