How to make a Sine Wave Generator

hey what's happening guys today I thought we would look at this particular circuit here I'll give you guys a few seconds to take a look at it and uh since you can't read this this is a 741 opamp any idea what's going on here no I bet one of you got it anyway this is another type of oscillator this is a wean Bridge oscillator and it is a form of a sinewave generator now let's uh take a look at a sketch of it here so I can give you guys a little better idea of what's going on so at the center we have our 741 opamp there's our output non-inverting input inverting input and we have plus 9 volt and Min - 9 volt now coming off of the output here we have a resistor and a capacitor that comes back into our non-inverting output and this provides a feedback loop now we are using 121 peak of farad and a 10K capacitor now this also continues on like this to another resistor and capacitor that are in parallel and they go to ground and this is also a 10K and a 121 P farad so this is half the circuit let me zoom out here a little bit and if we take this and we look at this section of the circuit here what we have created is a highpass filter and then if we look at this section of the circuit we have created a low pass but that's not all we are also coming off of here to another resistor which ties back to our inverting input and one more resistor right here that goes to ground now these values are critical to make this thing oscillate this one is 100k and this is 47k and then we take our output off of right there so this is the classic webridge oscillator although In fairness if it was really the classic it would have a light bulb in it the light bulb has to be a Tungsten bulb acted as an automatic gain control circuit and it was excellent it was uh first done by uh bill huet from hulet Packard back in the 40s now a couple of key points in order to get this to oscillate we have to have a gain in our amplifier portion right here that is equal to or greater than three okay if we don't it won't oscillate and just for those of you who are mathematically inclined the frequency can be figured out by one over 2 pi RC all right enough of the math let's bring our circuit back and let's zoom in here nice and tight maybe not that tight and take a look at what's going on so this is our 741 sure I'm nice and focused here pin one pin8 okay we have our V minus on pin four our v+ on pin seven pin one pin fo pin 8 Pin five and pin one are not connected so we have our output with the 10K resistor coming back over here and that is our first part of the Circ oh I'm sorry this is our 100K our 100K comes back over here to pin two which is the inverting part of the circuit and then it goes through this potentiometer which I've only connected two legs of see that's not connected and I have it tuned exactly to 47k so that is our inverting feedback loop now we also come out of here to the 10K into the first 121 puff capacitor then down to these two which are parall coming off of this and they both go to ground so let's zoom out here a little bit now since we're using the 741 opamp it is a split power supply and I am using a couple of 9volt batteries to power it so there we are we are powered up let's get a scope Probe on here connect our ground down here to the ground area and then up here now we're all nice and connected and let's swing up and have a look at the scope let's zoom in here all right turn this off now we have a good picture of the sine wave that's being output and that is a pretty nice looking wave there you can see we are at 500 molts per division so we are looking at about one volt Peak to Peak right no two volts Peak to Peak because that's one volt that's two volts and our frequency is hovering right around 86 khz with a period of 11.7 microseconds and you can see that is a very nice sine wave zoom in here as much as we can and there might just be the slightest hint of clipping on the top there you see that when we zoom out it becomes a little bit more apparent just just just a hair of clipping right there all right now where did I put my screwdriver so that I can show you what happens if we don't have that thing tuned one moment please all right sorry about that it had fallen under the desk so if I detune what happens here well you can see we've lost any semblance of this being a square wave and the more I detune it the more unstable it gets until it reaches the point where it no longer oscillates so if I bring that back and there you go we're right back where we came from or rather close to it you see our our frequency is falling off there a little bit and that's cuz I don't have that tuned right back exactly there our frequency's climbing back up now but that's it that is is the wean Bridge oscillator a very simple sinewave generator I hope you guys enjoyed this if you did give me a thumbs up comment share don't forget to subscribe and I'll catch you next time you're still here oh you like this sine waves all right well how about this then there is the 4ar transform of the wi Bridge don't tell anybody I showed you this

Channel: learnelectronics

Views: 119,911

Keywords: Wien Bridge Oscillator, sine wave generator, opamp, 741, tutorial, how to

Id: 57WgAduzoHs

Length: 11min 22sec (682 seconds)

Published: Thu Jun 01 2017