The 555SE Discrete 555 Timer

by Evil Mad Scientist

Surface mount soldering kit: Re-create one of the most classic, popular, and all-around useful chips of all time.

The "555SE" Discrete 555 timer is a surface-mount soldering kit that lets you build a faithful and functional transistor-scale replica of the NE555 timer integrated circuit, one of the most classic, popular, and all-around useful chips of all time.

Like its larger sibling the "Three Fives" soldering kit, the 555SE is an easy soldering kit that results in a working 555 timer, styled like an integrated circuit. However, while the Three Fives kit is a traditional through-hole soldering kit styled like a "DIP" packaged (through-hole) integrated circuit, the 555SE is a surface mount soldering kit, styled to look like a smaller "SOIC" packaged (surface mount) integrated circuit. This particular kit is called the "555SE" because it is the Surface-mount Edition, SOIC Edition, SMD Edition, and Small Edition of the 555 soldering kit.

The 555SE kit was designed by Eric Schlaepfer, working in collaboration with Evil Mad Scientist Laboratories. The kit is lovingly designed to resemble an (overgrown) integrated circuit, based around a black circuit board with clear solder mask so that you can see the wiring traces between the components. It comes complete with a beautiful aluminum display stand that gives the circuit board eight legs in the shape of SOIC-packaged integrated circuit pins. If you're familiar with our larger DIP-IC styled Three Fives kit, you'll find the 555SE to be smaller and built to the same scale, with half the lead pitch, and all surface-mount components. 

Building the kit

The 555SE is an easy-to-build surface-mount soldering kit. It includes the circuit board, resistors, and transistors 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.

To build the 555SE, basic electronic soldering skill and tools are required, but no additional knowledge of electronics is presumed or required. You provide standard surface-mount soldering tools: a soldering iron, solder (wire or paste), small metal tweezers, as well as a Phillips head screwdriver.

The kit features relatively large surface mount components (1206 and SOT-23), and is a great first surface-mount soldering kit if you're just getting started. However, if you are experienced at surface mount soldering and have tools like a hot air rework station or other equipment, you're welcome to use them for assembling this kit.

If you prefer a "through-hole" construction soldering kit, please take a look at the sibling kit, the "Three Fives" kit.

Using the 555SE Discrete 555 Timer

The 555SE circuit is a direct implementation of the "equivalent circuit" from the NE555 datasheet, built up using resistors and individual 2N3904 and 2N3906 transistors. It comes with terminal posts and solder points so that you can actually connect to it and build up any number of 555 timer and oscillator circuits. Using those terminal posts and solder points, you can hook up with with bare wires, lugs, alligator clips, and/or solder joints-- however you see fit.

And unlike the chip version, you can even hook up probes to monitor what goes on inside the circuit.

There are a remarkably large number of excellent 555 example circuits available on the internet (for example, over 100 here), as well as on other sites across the internet.

While the 555SE will work without modification in the majority of example circuits, some performance characteristics are different than those of 555 integrated circuits; please refer to the Absolute Maximum Ratings and Electrical Characteristics in the datasheet for additional details.

Additional specifications

Kit size

  • The 555SE printed circuit board is 2.559 × 2.047 inches (6.5 × 5.2 cm) in area, and (nominally) 0.062" (1.6 mm) thick.
  • Including the "Integrated Circuit Legs" stand and terminal posts, the overall size of the assembled kit is nominally 2.559 × 3.066 × 0.800 inches (6.5 × 7.8 × 2.0 cm).

Materials and construction

  • The decorative stand is smooth to the touch and made of anodized aluminum.
  • The circuit board in the kit is black, with gold plated contacts, a clear solder mask finish, and four countersunk mounting holes.
  • Eight 4-40 surface-mount threaded inserts for the terminal posts are included with the kit.
  • The included terminal post screws are stainless steel thumbscrews with color-coded plastic caps (1 red, 1 black, 6 gray).
  • All materials (including the circuit board and stand) are RoHS complaint (lead free).

Downloads and additional resources

  • Additional specifications are given in the kit's datasheet (1.7 MB PDF file).
  • Kit assembly instructions (3.3 MB PDF file). Printed instructions are included with the kit.
  • Evil Mad Scientist have written a detailed educational supplement for this kit, which goes into detail about how the circuit works: "Principles of Operation" (1 MB PDF)
  • The central documentation page for the kit is found here on the documentation wiki.