Maker Pro
Maker Pro

Threshold Circuit - Warning - I know practically nothing about building circuits

Hi

First off this is my first post in this forum so I apologies if I have posted this in the wrong place or if this thread is unsuitable for this forum.

Though I have a lot of background knowledge about science and how components of a circuit may work I have very little knowledge about actual circuit building, so once more I must apologies if I do not understand any terms used.

I require a circuit that when triggers some form of motor or LED when an input voltage falls below some threshold. That is when this voltage drops the LED turns on. I am attempting to teach myself some amount of electronics but this is unfortunately is moving too slow as I want to use this idea in an up and coming project.

Any and all help would be appreciated.
Thank you
 
This can be accomplished with a comparator. It compares two voltages its output depends on which is higher than the other. You feed it a reference voltage (the threshold) and the voltage to be compared. If you have a regulated supply, the reference can be as simple as a voltage divider (two resistors). For battery operation, a separate voltage reference should be used.

Bob
 
Bobs right on the mark, but if your input is not rock solid then your LED could flicker on and off. Why not try a comparator with a bit of positive feedback. This gives a bit of a lazy circuit who's thresholds change when the device switches. This is a Schmitt trigger and you are applying a bit of hysteresis. Google Schmitt trigger op-amp and you will see what I mean.
Adam
 

KrisBlueNZ

Sadly passed away in 2015
The 555 timer contains two comparators with fixed threshold voltages and can be connected to operate as a Schmitt trigger. It can also drive LEDs and small motors directly. Google 555 Schmitt.
 
Top