Delays And Timers In LTSpice (no 555)

If you need a precise time, you could use a microcontroller. Of course, then all your friends will say “Could have done that with a 555!” But the 555 isn’t magic — it uses a capacitor and a comparator in different configurations to work. Want to understand what’s going on inside? [Mano Arrostita] has a video about simulating delay and timer circuits in LTSpice.

The video isn’t specifically about the 555, but it does show how the basic circuits inside a timer chip work. The idea is simple: a capacitor will charge through a resistor with an exponential curve. If you prefer, you can charge with a constant current source and get a nice linear charge.

You can watch the voltage as the capacitor charges and when it reaches a certain point, you know a certain amount of time has passed. The discharge works the same way, of course.

We like examining circuits for learning with a simulator, either LTSpice or something like Falstad. It is easier than breadboarding and encourages making changes that would be more difficult on a real breadboard. If you want a refresher on LTSpice or current sources, you can kill two birds with one stone.

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A Pair Of Projects To Scare The Trick-or-Treaters

The countdown is on! There’s only a few days left until Halloween, and if you’re still looking for something to spice up the experience for the kids heading to your door, [MagicWolfi] has just what you need. He’s put together two motion-sensing projects that are sure to startle any trick-or-treater.

The first project is a chain of LED-lit pumpkins that are activated by a motion sensor. A set of inverters paired with RC delay lines light up the pumpkins sequentially. They are arranged almost like a strand of Christmas lights and are powered by AA batteries, so in theory they could be expanded to make a strand as long as needed. The project was inspired by a motion-sensing dress and works pretty well as a Halloween decoration!

9378581414283863206[MagicWolfi] is pairing the LED pumpkins with his second project which uses another motion sensor to play scary sound effects. Dubbed the Scare-o-Matic, this device uses a 45-millimeter speaker connected to a SparkFun microSD audio module to produce the scary sound effects. Each time it is triggered it plays a different sound from the list. There are videos and schematics for each of these projects on the project sites if you are interested in recreating any of these before Friday!