1 sec ON - 1 sec OFF - Page 1
Forum section: electronics / beginners

author: pub2024
author_rank: Contributor
timestamp: January 26, 2024, 06:25:30 pm
content: Please give me some advice how I could create the following circuit to transform 1Vrms sine into 1 sec pulses. ON - 1 sec. OFF and still like that?I also posted below an image with a sketch of what I want to do.

author: oPossum
author_rank: Super Contributor
timestamp: January 26, 2024, 06:51:45 pm
content: 74HC14 (sine to square) -> 74HC390 (divide by 100)

author: sparkydog
author_rank: Regular Contributor
timestamp: January 26, 2024, 06:52:58 pm
content: ...use a voltage comparator? This is a fairly basic problem;a web searchoffers many possible solutions...Be sure, however, that you're aware of the issues with feeding negative input voltage to an op amp and how to correctly address them.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 26, 2024, 07:10:23 pm
content: Quote from: sparkydog on January 26, 2024, 06:52:58 pmmy first thought too (without carefully reading)... but comparator cannot divide... if what OP wants is 100Hz sine -> 1Hz square, then opposum is right..

author: pub2024
author_rank: Contributor
timestamp: January 26, 2024, 07:21:09 pm
content: Quote from: oPossum on January 26, 2024, 06:51:45 pmThank you for the advice. Can you show me an application with these circuits!

author: oPossum
author_rank: Super Contributor
timestamp: January 26, 2024, 07:32:00 pm
content: Schematic attached

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2024, 08:08:28 pm
content: First the O.P. needs to specify the range of input conditions that shall result in the 1s on / 1s off output. e.g. Should 1V RMS 60Hz give the same output? What about 0.1V more or less?Second the O.P. needs to specify the output when the input conditions are not met.Third, the O.P. needs to specify tolerances for the output signal. An upper limit of 5V has already been specified, but it still needs a lower limit voltage and tolerances for period and duty cycle (or on and off time), and max. output current or specs on the load it must drive.Fourth, the O.P. needs to state what power sources are available, or is it a requirement to power it entirely from the input signal?Edit: added need for output current specs

author: pub2024
author_rank: Contributor
timestamp: January 26, 2024, 08:28:53 pm
content: The rectangular impulses on the output must also appear when on the input we have at least: 0.1Vrms. To do this, I will add a buffer with an operational amplifier that will bring at least 1Vrms to the 74HC14 input - is that enough ?

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 26, 2024, 08:51:38 pm
content: First take a look at the74HC14 datasheetand check the threshold voltages for what it needs. There is a dependence on supply voltage and temperature.Now design for a worst case scenario of the to expect input voltage range and add an amplifier on the input to supply the correct range for the 74HC14 to make it work.Also make sure that a to high input voltage does not destroy your circuit, so add some protection if needed. Also the 74HC14 does not like negative voltages on its input, so the resistors in the schematic given by oPossum need to be sized correctly to make sure the max ratings are not surpassed, or add a schottky diode to ground for protection.

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2024, 08:54:42 pm
content: Quote from: pub2024 on January 26, 2024, 08:28:53 pmThat makes it considerably harder - 0.1V is low enough that you may have to worry about noise pickup being mistaken for the required signal.Read my list of questions above and answer them and you'll be offered better solutions. The more answers we get, the better the results. Note that you should *NOT* specify tolerances any tighter than required, or it may make the solution far more expensive or even impossible, missing out on a simple circuit that cant meet the closer tolerances.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: January 29, 2024, 01:15:28 am
content: I wonder how many college professors monitor this forum.