Hundreds of 555 Timers Come Together to Form… a Timer

According to Doug Lowe, author of Electronics All-in-One for Dummies, “the 555 timer chip, developed in 1970, is probably the most popular integrated circuit ever made. By some estimates, more than a billion of them are manufactured every year.” A 555 timer can work in different modes and for different purposes, but a single unit most often acts as an oscillator (hence the name) to increase a count at regular intervals or activate some other part of a circuit. But Jesse Farrell took the name a little too literally and used hundreds of 555 timer ICs to build an actual timer.

Farrell started work on this project in response to Hackaday’s 2021 555 Timer Contest, which challenged participants to come up with interesting uses for the iconic IC. Because 555 timers are so versatile and suited to a wide range of applications, that contest received a whopping 74 entries. Farrell wasn’t a winner, but his project is still noteworthy. Creating a simple timer like this with a microcontroller would be trivial, but this device functions using just 555 timers and discrete components. It uses 276 NE555PWR timer ICs in total, which sounds like a lot until you realize how much logic they need to handle.

Those functions include:

• User input to set the timer, requiring the injection of clock pulses into the counter circuit.
• A 16-bit counter (four bits for each of the four digits), which counts down in base 10 from 9999 to 0000.
• A clock to refresh the 7-segment displays.
• A clock that drives the counter at one tick per minute.
• Input for the 7-segment displays, with the output mapped to the pins of the display.
• A multiplexer that controls which 7-segment display receives input.
• A selector that tells the multiplexer which 7-segment display to feed, along with a decoder.
• 4-bit storage for each of the four digits.
• A buzzer that sounds when the countdown reaches 0000.

These functions are overwhelming and the circuit to implement them is very complex. Farrell provides detailed explanations of every function and how they fit into the circuit if you want to dive into the deep end. But the final implementation relies on eight individual PCBs. The first contains the display, the buzzer, input buttons, and dip switches. The other seven boards contain all of the 555 timers and discrete components.

We can’t help but love this project, as it accomplishes a very simple task in the most complicated way that we can imagine. It also illustrates the versatility of the humble 555 timer.