# Voltage controlled oscillator with LM324 and 555 timer

Discussion in 'Electronics Homework Help' started by CraziestOzzy, Jul 4, 2012.

1. ### CraziestOzzy

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Firstly a big g'day from Down Under.
I require some help if you guys and gals don't mind assisting?
I have done the hard yards this past week, searching the WWW and fiddling with circuit simulators to solve a problem.
I am at the end of my tether and am now here as a newbie asking questions to get me back on my horse.
Here are the nuts and bolts:

I am wanting to control a motor through PWM.
I wish to control a DC motor speed for a 6 volt brush motor through a linear pot and also have that speed oscillate (throb) with the oscillation frequency controlled by a linear pot to have a complete cycle peak to peak of around 1 to 5 seconds.
I can create a PWM using either an OpAmp or a 555 timer.
I can also create a crude sine wave with either IC and output a positive voltage output and manipulate that wave to the low frequency of around 1 to 30Hz.

The challenge for me is combining the two together...I just don't know how to describe what I want in a Google search.
I am at the moment using the 555 timer to create a sine wave in a brutal manner and using an OpAmp as a voltage controlled pulse oscillator.

So here is the simulation results that I have so far created (note the MARK chnages width):

you can see the sine wave controlling the pulse frequency. The pulse frequency can be controlled seperate to the sine wave bya pot and also be influenced by the sine wave ... hope that ain't confusing
That's good so far, but what is this process called?
I have an issue...the circuit I created to produce this frankenstein thingy, roughly works but shifts the width of the each pulse MARK relative to the volatge in the sine wave.
I do need to know how I can keep the MARK of the pulse the same width and have the SPACE change. Any idea?

..and here is the completed circuit and do excuse my layout...I did my best to make it easy to read. I think there is some stuff that is not needed and also think there is stuff I need

Basically, the 555 produces a sine wave as a result of cap C1 charging and discharging and the R3 pot controls the width of the sine wave.
(I butchered that idea from a "police siren" with a 555 timer...saw a nice sine wave
I could not for the life of me use another 555 timer to get the effect I want, that of a shifting pulse frequency relative to a sinewave. I used "proper" setups for dual timers with dividers etc and just could not get it working due to the 555 stealing voltage 1/3 and 2/3...so enter the OpAmp as the second IC.
I have referenced U2C OpAmp to the output of the 555 timer (as opposed to using a typical voltage divider to the 6volt supply volatge).
The U2B has a pot (R8) that controls the pulse output frequency.
Ignore the discreets attached to the final output from U2A (2n3904). The final output here will be attached to a TIP31c that will drive the Dc motor.

I hope that was as clear as mud.
If you have an alternative super simple method to have a pulse frequency shift relative to a sine wave without having the mark of each pulse peak shift it's width relative to the voltage, I would love some thoughts.
Any add-ons or exclusions to help improve my circuit would be greatly appreciated.

To help you guys, if you think up another circuit...I have included my list of at-hand IC's:

555 TIMER
74HC14D HEX Inverting Schmitt Trigger
MC34025P Double Ended PWM
TL1431CD SMD Precision Programmable Voltage Reference
UCC27322 Gate Driver for MOSFET/IGBT 9A
MC33035 Brushless DC Motor Controller
CA3140E 4.5MHz BiMOS Op-Amp
OP07CP LOW-OFFSET VOLTAGE Op-Amp
LM311N VOLT COMPARATOR
BQ2004/2002 NiCd charger
UCC27322P Mosfet Driver
LM311N
74HCT688
74HCT73
74HCT04
74HC164

Last edited: Jul 4, 2012
CraziestOzzy, Jul 4, 2012

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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The approach I would consider is a voltage to frequency converter triggering a monostable.

This would generate fixed length pulses where the gap between them varies.

You feed in your sine wave (which represents the requuired speed of your motor) which causes the frequency of another signal to go up and down (essentially frequency modulation). The fixed ON time would convert the frequency to a duty cycle, so your duty cycle would vary with your sine wave.

With some constraints, a variable voltage applied to pin 5 of a 555 will change the frequency of the signal it produces. Another 555 can be set u as a monostable to produce fixed length pulses triggered by the first 555. This circuit requires that the control voltage be between 1/3 Vcc and Vcc, and a higher voltage will result in a lower frequency. The mapping of voltage to frequency is not linear.

(*steve*), Jul 4, 2012

3. ### CraziestOzzy

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Looking at the search terms "voltage, frequency, converter, triggering, monostable" inside Google.
Have found a lot of circuits I have allready seen, most don't work or are poorly laid out have severly compressed images that contain a vital circuit.
You get that.
Found some gems and working a few ideas right now.

Any other input would still be appreciated, ideas greatly received.

...should get me 100/100 for my assignment

CraziestOzzy, Jul 4, 2012
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Please be aware that we don't like giving people answers to their homework.

It's bad enough that you didn't identify this as homework. It's another thing to gloat about it.

Last edited: Jul 5, 2012
(*steve*), Jul 5, 2012
5. ### CraziestOzzy

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mate...lighten up
I am over 40 years old, been there and done that and threw in my comment as a joke
...and take no offense from my comment, I am aware of pimple snots doing the lazy thing and wanting to be spoon fed ...hate it as much as you

Last edited: Jul 5, 2012
CraziestOzzy, Jul 5, 2012

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