Basic components #002 - Schmitt Trigger | configurations

it's been a while since our last basic components video right last time we have seen the operational amplifier and how to use it well now this is a Schmitt trigger inverter the cd40 10 6 B and that's what we will see in today's video before we start please leave a comment in the comment section below with other basic components that you would like to see in the future so guys that being said let's get started this video is sponsored by gel CPCB if you want professional made PCBs for a very low price you should try their services their prototyping PCBs prices are so low that now for a lot of the small circuits that I design I also make a PCB that will keep my projects cleaner more professional look and better performance than the homemade versions so guys upload the Gerber files to their webpage review the design and starting from only $2.00 order 10 PCBs for your project what's up my friends welcome back in the last video we have seen that we could use an operational amplifier to compare signals and give a high or low output depending on which input is higher than the other one well the Schmitt trigger is used for kind of the same purpose but with something extra for that let's see first the comparator configuration of the amplifier if you remember we have two inputs and one output if I place a potentiometer at the negative input we can change the threshold value for when the signal as the output will pass too high or too low we can lower or increase this threshold so let's say that to place a trash hold of 3 volts using the potentiometer now at the positive input we have a signal that oscillates and we want to read that so we want each oscillation to become a square wave each time the input is higher than 3 volts we have a high post at the output that's pretty easy right but what if the input has noise let's do the same but now using this wave it is the same signal but with some noise ok so right at this oscillation after the signal passes three volts we have a little bit of noise and a small ripple that goes below 3 volts that will result in a short low post at the output which would be an error since we don't want that this is the wave that we want and this is the one with noise so that's why we use a Schmitt trigger because it has to trash holes voltage levels one for the rising edge and the other one for the falling edge let's see the same signal now but with two different results values the input gets over three volts and now the output is high no I mean it's low because it is also an inverter if you want it to be a high post just invert the signal two times okay so then the input has the ripple and gets a little bit below 3 volts but since it didn't pass below the second threshold the output didn't change neither so now we get the good signal that we want so that is the main function of a Schmitt trigger to convert a noisy signal to a good square wave that could be then read by microcontroller or other digital components lots of ICS already have schmick triggers integrated in their inputs we will look over some other options to create our Schmitt trigger but first let's test it I place the comparator configuration of the op-amp on my breadboard I now apply a 15 Hertz sine wave of 10 volts peak-to-peak sine wave is not the best signal for this example since it will be half time over zero and the other half below zero so it is very easy to set a threshold but anyway I place the threshold with the potentiometer at around 4 volts now here is the output each time the sine wave is above 4 volts I have a high Square pose but now let's add some ripple to simulate noise I increase the level of the noise and there you have it now I have another small pose if I get the ripple even bigger I get more and more error pauses and if you would want to count them you will get a wrong amount but now I do the same with the cd40 10 6b Schmitt trigger and now I have good results I have a Schmidt inverter so I had to invert the signal two times in order to get positive poles as you can see now with even bigger ripples I still have a good wave but of course if I increase the noise even more I will eventually get errors as well since now I pass both threshold values of the trigger see the datasheet of your Schmitt trigger in order to know more about it okay so let's say that you don't have a Schmitt trigger I see you only have op amp's well here is a Schmitt trigger configuration made with op amps negative input connected to ground so that implies that the v+ point will be ground as well so we have these two equations the current that passes our one is the same that passes our two since v+ is zero so we get that VN divided by r1 it's equal to negative V out divided by r2 so that tells us that V in is equal to negative R 1 divided by r2 and multiplied by the V out where the output have the values of minimum and maximum supply voltage in this case let's say that the op-amp is supplied to plus and minus 5 volts so V out could be plus and minus 5 volts also let's say that r1 is 1 K ohms and r2 is 1.7 K ohms so we get that for the switch to be made we need V in to be equal to 1 K divided by 1 point 7 k and x plus or minus 5 volts so the switch will be made at plus minus 3 volts right so there you have it we have 2 threshold values when the input is rising from negative five volt to positive five volts when we reach positive three volts the output will be high but on the falling edge when we get from positive five volts to negative when we reach minus 3 volts the output will be low and here is why the icon of a Schmitt trigger are these two threshold values okay so what if we want different threshold values let's say that we want positive three point five volts and positive two volts for that we will use this configuration with three resistors here we have the equations for the rising and falling threshold values and let's say that we supply the op-amp with five volts when V out is ground we actually have r3 and r2 connected to ground so there is a barrel of those two resistors so we get a voltage divider like this so let's say that the resistor values are r1 equal to six point eight K and R 2 and R 3 are equal to 10k so we get the falling edge threshold of 2.1 volts and when V out is high so 5 volts we get this equation so with the same resistor values we get a threshold voltage of 3 point 5 volts for the rising edge so there you have it the rising value is three point five volts and the folding threshold value is two point one volts and we've got our Schmitt trigger made with op amps fine-tuning the resistor values you could set the threshold below you have links for my webpage for more examples and options on how to make a Schmitt trigger also using BJT transistors and resistors I hope you enjoyed this tutorial and that you have learned something new make sure to hit the subscribe button and the notification bell in order to see future videos and also click the like button like crazy and share this video with your friends remember if you consider helping my project check my patreon page as well thanks again and see you later guys [Music]

Channel: Electronoobs

Views: 19,921

Keywords: tutorial, schmitt, trigger, opam, operational, amplifier, configuration, non, symmetrical, threshold, basic, components

Id: d-7Oyd8o8hE

Length: 8min 57sec (537 seconds)

Published: Sun Sep 02 2018