66% or better

CMOS logic clock tracks 24-hour time

Here’s an IC logic project that displays 24-hour time. Planning was the name of the game for this project. [Mattosx] took the time to layout his design as a PCB in order to avoid the wiring nightmare when build with point-to-point connections.

Much of the complexity is caused by the display itself. Each of the six digits has its own binary-coded decimal chip and array of discrete resistors. Timekeeping is handled by six decade counters, two divider chips, one AND gate chip, and one OR gate chip. He chose a SOIC crystal oscillator chip as the clock signal. We’re more partial to the idea of using mains voltage as the clock signal.

[Mattosx] posted the board artwork if you’d like to etch your own 5″x8″ PCB. Just make sure you read through all of his notes as not all of the chips are oriented in the same direction.

[via Reddit]

Resistor substitution box

[Vincent] on the EEVblog forums had an idea for an inexpensive resistor substitution decade box.

The build uses cheap decimal thumbwheel switches he bought on eBay. Each switch is wired up with resistors for each digit, and each switch is wired up in series. The result is a small, easy to read resistor box with a range of 1 Ω to 10 MΩ.

[Read more...]

Clock sans-microcontroller

This clock requires no microcontroller. It’s actually a digital logic counter that functions as a timepiece. [BlackCow] used six decade counters to track seconds, minutes, and hours. The output is displayed on four 7-segment digits using BCD-7-segment decoders that you can learn about in our binary encoded decimal post. The actual timekeeping is done by a quartz clock circuit he pulled from a Mickey Mouse clock. This would be a perfect circuit to build in a digital logic simulator, just follow the schematic and learn as you go.

Beginner Concepts: Binary-coded decimal

A rudimentary understanding of digital logic and simple integrated circuits is critical if you’re ever going to pull off some really gnarly hacks. [Daniel] put together an explanation about the use of 4511 BCD 7-segment drivers. These chips take binary data in and output decimal data to a 7-segment LED display. In short, they can read 0b1001 from input pins and light the numeral ’9′ on the display. The best part is that you can build this example circuit in the Atanua logic simulator without ordering parts. We love zero-cost learning!