Breadboard 555 Timer

This is a 555 timer built on a breadboard. The 555 timer is an 8 pin IC chip, but I thought it would be fun to build my own on a breadboard. There are five sections to the chip, it will be built on five 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 555, and a datasheet with a schematic, is located here. They also sell the bare circuit board from the kit if you choose to source your own parts.

To build it you will need:

A wood base 13 by 7 inches.

• 10 - #6 round head wood screws 3/4 inches long
• 10 - #6 nylon spacers 1/4 inch long
• #6 Fibre washer (Purchased locally at Micro-Center)
• 5 - Adafruit Perma-Proto Boards http://www.adafruit.com/products/1606
• Adafruit Perma-Proto 1/4 size Board https://www.adafruit.com/products/1608
• 22 Gauge Hook-Up Wire https://www.sparkfun.com/products/11367
• 13 - 2N3904 NPN Transistor http://www.dipmicro.com/store/2N3904
• 13 - 2N3906 PNP Transistor http://www.dipmicro.com/store/2N3906
• 1 - 100 Ohm 1/4 Watt 1% resistor http://www.dipmicro.com/store/R2F10-4***
• 1 - 220 Ohm 1/4 Watt 1% resistor http://www.dipmicro.com/store/R2F22-4
• 1 - 820 Ohm 1/4 Watt 1% resistor http://www.dipmicro.com/store/R2F82-4
• 1 - 1 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R3F10-4
• 1 - 3.9 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R3F39-4
• 7 - 4.7 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R3F47-4
• 1 - 6.8 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R3F68-4
• 1 - 10 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R4F10-4
• 1 - 15 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R4F15-4
• 2 - 100 K 1/4 Watt 1% resistor http://www.dipmicro.com/store/R5F10-4
• 2 - DC Barrel Jacks http://www.adafruit.com/products/373
• 8 pin IC socket https://www.adafruit.com/products/2202
• 555 Timer IC chip http://www.dipmicro.com/store/NE555P
• 3 - Strips of female headers https://www.sparkfun.com/products/115
• 9V battery clip http://www.adafruit.com/product/80
• 9 Volt Battery

These items are needed only for assembly:

• 2 - Breadboards http://www.adafruit.com/products/239**
• Long male headers http://www.adafruit.com/products/400

In addition I needed a digital multimeter because the blue bodied resistors with five bands are very hard to read with my old eyes.

These items are needed for the three testing steps:

• Breadboard (mentioned above)
• 3 - 470 Ohm resistors http://www.dipmicro.com/store/R2F47-4
• 10 K 1/4 Watt resistor http://www.dipmicro.com/store/R4F10-4
• 10 K potentiometer https://www.adafruit.com/products/356
• Red LED https://www.sparkfun.com/products/9590
• Green LED https://www.sparkfun.com/products/9650
• Yellow LED https://www.sparkfun.com/products/9594
• 22 Gauge hookup wire (mentioned above)

The wood base was a piece of scrap from one of my wife's projects. The wood screws, spacers, and the nine volt battery were purchased at the local Ace hardware store.

** One breadboard needs to be 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 you solder them.

*** This resistor kit plus 5 4.7 K and resistors is all the resistors you need to complete this project, and many extras.

I made my base out of a piece of scrap wood 6.75 by 13.5 by .75 inches thick.

Find the center of your base 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.

Mark the location of holes 2 1/2 inches to the left and right of the center holes, centered vertically.

Mark the location of holes 5 inches to the left and right of the center holes, centered vertically.

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

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 Reset/Discharge board.

For this board row number one is on the bottom, for the rest of the boards it will be on top.

Cut two pieces with two connectors and two pieces with eight 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 two male headers with two pins each in another breadboard spaced to hold the eight pin female headers, again refer to the first photo.

Place the two, two pin female headers and two eight pin female headers on the male headers, like in the second photo.

The third photo shows the Perma Proto board placed upside down on the two breadboards. The headers in the power rails are on the right in row sixty.

The eight pin headers are in holes B 1-8 and C1-8.

Solder the eight pin headers and the two pin header on the opposite side of the board from the eight pin header. The other two pin header is just there for balance, do not solder it.

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

Place a 2 pin long male header in the breadboard in holes A2-3, A5-6, A18-A19, and A31-B31.

Place a 2 pin female header on top of the male headers on A2-3 and A5-6.

Place a 1 pin female header on top of the male headers on A19, and A31.

The header in row J is just there for balance.

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.

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

Cut off the side pin on the barrel jack and solder the back (+) lead into hole A53 then solder the other lead into the ground rail.

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

The yellow wire between holes E2 and F2 Should be a little long to allow room for the screw when mounting.

The resistor between I15 and I19 is a 100 Ohm.

The resistor between F22 and F26 is a 100K.

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 Discharge/Reset board on the right side of the base with the eight pin connectors and the barrel jack on the right. One of the 1/4 inch nylon spacers goes under each screw. 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.

On this board, and all the rest, row number one will be at the top of the board.

Build the circuit according to the diagrams.

Follow the same procedure as on the first board:

• Headers
• Wires
• Resistors
• Transistors

The resistor between D17 and D21 is a 3.9 K resistor. Both leads of the resistor are soldered into the same holes as the wires attached to it.

The resistor between D35 and F35 is a 220 Ohm resistor.

Mount the output board next to the reset/discharge board with row one at the top.

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

Connect a white wire from J21 on the output board to J3 on the reset/discharge board.

Connect a white wire from J40 on the output board to J18 on the reset/discharge board.

Before going any further now would be a good time to test the work so far.

The female headers at B1-8 and C1-8 are the eight pins on the 555, you have two connections to each pin. When I say pin I am referring to the these headers.

The red LED lights when the output pin (3) is low.

The green LED lights when the output pin is high.

The yellow LED is connected to the discharge pin (7), when the output pin goes low it should light. When the output pin is low the discharge pin shorts directly to ground. When it is connected to positive voltage it must go through some resistance or too much current will destroy the transistor at B14-16 on the reset/discharge board.

Build the circuit as shown in the diagram.

Connect the wire from the 10K resistor to A19 on the output board and plug in the battery.

The green LED should light.

When you briefly touch the other wire from the 10K resistor to the connector at A35 the green LED should go out and the red and yellow LEDs should light.

Save this breadboard, you will need it for another test later.

Build the circuit according to the diagrams and the procedures explained in previous steps..

The resistor from D10 to D14 is a 15K.

The resistor from H10 to H14 is a 6.8 K.

The resistors at D16 to F16 and I24 to Ground are both 4.7 K.

Mount the flip-flop board next to the output board.

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

Cut a blue wire and connect J34 on the flip-flop board to J31 on the discharge/reset board.

Cut a blue wire and connect J19 on the flip-flop board to A19 on the output board.

Cut a blue wire and connect J21 on the flip-flop board to A35 on the output board.

And now it's time for another test.

Use the same breadboard you used in the first test.

Disconnect one of the wires from the 10 K resistor.

Quickly touch the wire from the 10 K resistor to the connector at A48 on the flip-flop board and remove it.

The green LED should turn on and stay lit.

Quickly touch the wire from the 10 K resistor to the connector at A16 on the flip-flop board and remove it.

The red and yellow LEDs should turn on and stay lit.

Build the circuit according to the diagrams and the procedures explained in previous steps..

The three resistors in a row on the left side of the board are all 4.7 K.

The resistor from G3 to the G7 is a 1 K.

The resistor from F28 to F32 is a 100 K.

Mount the trigger comparator board next to the flip-flop board.

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

Cut a yellow wire and connect J25 on the trigger comparator board to J2 on the discharge/reset board.

Cut a yellow wire and connect J8 on the trigger comparator board to A10 on the flip-flop board.

Cut a yellow wire and connect J28 on the trigger comparator board to A48 on the flip-flop board.

The resistor from B3-B7 and the resistor from E23-F23 are both 4.7 K.

The resistor from D11-D15 is 820 Ohm.

The resistor from I45 to the ground rail is 10 K.

Mount the threshold comparator board next to the trigger comparator board.

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

Cut a green wire and connect J17 on the threshold comparator board to A16 on the flip-flop board.

Cut a green wire and connect J30 on the threshold comparator board to J6 on the discharge/reset board.

Cut a green wire and connect J39 on the threshold comparator board to A42 on the trigger comparator board.

Cut a green wire and connect J40 on the threshold comparator board to J5 on the discharge/reset board.

After finishing this it occurred to me that it would be possible to make a mistake wiring something to it and damage it. The first picture shows 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 25 cent 555 and save damage to your project.

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For this final test remove the 10 K resistor on your test breadboard and the wires attached to it.

Remove the yellow LED connected to pin seven, it's resistor and all the wires connected to it. You don't need them any more, the discharge pin has been tested enough.

Cut a short wire and connect pin 4 to pin 8.

Cut another short wire and connect pin 2 to pin 6.

Connect the 10 K potentiometer, one of the end terminals goes to the ground rail and the other to the positive rail. The center terminal, called the wiper, goes to pin 6.

You have constructed a not gate. When the pot is turned to a low voltage the green LED will light indicating that the output pin is high. When the pot is turned to a high voltage the output pin will be low and the red LED will be lit. Turn the pot to the center of it's travel. You will notice that you can move the pot in either direction and nothing will change. Between 1/3 and 2/3 of the voltage range is dead space. This is called hysteresis. This is a high hysteresis not gate.