A 7400 frequency counter, on perfboard


jaeblog published a new build:

I like perfboard, especially the ones with plated trough holes. But I also like SMD components, and more and more fun IC’s are not available in DIP. So a while ago I designed some perfboard with 1.27mm pitch, making some SMD parts like SOIC stuff easy to prototype on it, and also mix THT and SMD stuff.
Looking for a nice little project to build on it, I came across a frequency counter made with 7400 logic, perhaps not the most efficient approach, but a fun one at that. I made a few changed to the design, partly because of some components I already had like the 74HC160 and 4543 (yes, not 7400 but still logic :P) and partly to improve on the design, for example by adding a 10Mhz oscillator instead of a NE555 as the clock source. The current end result looks like this, a case is ordered and a follow up post will be made when the project is nicely tucked away in a case.

More details on Just another electronics blog.

Dead-Bug Logic Probe in a Magic Marker

Logic probes are simple but handy tools that can be had for a couple of bucks. They may not be the sexiest pieces of test gear, nor the most versatile, but they have their place, and building your own logic probe is a great way to understand the tool’s strength and weaknesses.

[Jxnblk]’s take on the logic probe is based on a circuit by [Tony van Roon]. The design hearkens back to a simpler time and is based on components that would have been easy to pick up at any Radio Shack once upon a time. The logic section is centered on the venerable 7400 quad 2-input NAND gate in the classic 14-pin DIP format. The gates light separate LEDs for high and low logic levels, and a 555 timer chip in a one-shot configuration acts as a pulse stretcher to catch transients. The DIP packages lend themselves to quick and dirty “dead bug” construction, and the whole thing fits nicely into a discarded marking pen.


It’s a simple build and a nice form factor for a useful tool, but for an even slimmer package like an old syringe you’ll probably have to go with SMD components. And when you graduate from the simple logic probe, you might want to check out the capabilities of this smart probe.

Filed under: classic hacks, tool hacks