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I would like to make a VCO using 555, audio speaker output, input 10 mv to 200 mv. Need diagram and parts list.
With gain control and volume control. Thanks for your assistance.
The 555 actually has a control input that will vary the output frequency. You set the 555 up as an astable oscillator then use the control input to change the frequency.
I think Alec was referring to pin 5. Ironically it is called the "control voltage" pin and is frequently used to create a VCO, as it sets the threshold voltage:
A 555 makes a buzzing sound in a speaker because its output is not a smooth sinewave, it is a rectangular wave that has many harmonics.
Its maximum allowed output current is only 200mA so if the output is capacitor-coupled to an 8 ohm speaker then the maximum allowed peak output is 200mA x 8 ohms= 1.6V which will make a low sound level.
This reference states that the control voltage input of the 555 in the astable mode should be no lower than 1.7V, for reason not stated. So, your control input would have to be level shifted/amplified, if that is true.
**broken link removed**
"The control voltage may be varied from 45 to 90% of the Vcc in the monostable mode, making it possible to control the width of the output pulse independently of RC. When it is used in the astable mode, the control voltage can be varied from 1.7V to the full Vcc. Varying the voltage in the astable mode will produce a frequency modulated (FM) output."
This is where it gets a little complicated for me. The 555 as I understand it will produce an audio frequency that will vary proportionally with the input voltage ... and the voltage range I want to work with is a varying voltage of 10 mv to 200 mv would have to be in range required by the 555 voltage input to produce the audio tone changes of the input volts, hi and lo tones. So I suppose some additional circuit would be required to amplify the volts to the working range of the 555. By the way, I did check online on the 555, lots of stuff, but it did not lead me to a working circuit that I think would do the job. Thank you guys for taking an interest in this venture. If the 555 can not do the job, is there another way to skin the cat?
You can shift signal level to 1,7v and amplify it to make it change from 1,7v to Vcc
This is done by any opamp, like lm358 , here is circuit example https://www.daycounter.com/Circuits/OpAmp-Level-Shifter/OpAmp-Level-Shifter.phtml
But you can also make VCO using only opamp, circuit is on LM358 datasheet's first page, or just google for operational amplifier vso.
Presumably the 10mV-200mV control signal is a DC voltage?
What is its source?
If you want an audio output a 555 is not the best solution. It will produce a horrible sound (rectangular waveform). A sinewave would be ideal (more melodic) but is not easy to generate with a voltage-controlled widely-varying frequency. A triangle-wave generator might be a reasonable compromise.
The 555 timer has very poor accruacy. I have one that I use to operate an car ignition coil to start a model airplane engine. When the air temperature changes the frequency change is very noticable. When the 555 IC warms up the frequency change is very noticable too. The frequency can drift off so far my ignition coil will no longer work. I have a variable resistor I can turn it for best Hz for maximum high voltage spark.
If you buy the book called, TTL Cookbook it gives you circuits and all the design information you need to build the perfect circuit. For best results you need some temperature control devices like thermistors.
The 555 timer is not effected much by voltage. It has an operating range of 5 to 18 volts but some brands of 555 timers will self distruct above 15 volts.
The output wave can be made to be just about anything you like. You can make a square wave with duty cycle of 50/50 or 10/90 or 90/10 or smaller as I recall 5/95 and 95/5 is about the limit. You can make saw tooth waves, and with some expermenting get pretty close to sine wave. You can also combine 2 frequencies to produce tones.
In my entire electronics career I never used an ordinary 555. A few years ago I used a Cmos 555.
I replaced my TTL Cookbook with a Cmos cookbook about 30 years ago. I have not used old high power TTL ever since.
In my entire electronics career I never used an ordinary 555. A few years ago I used a Cmos 555.
I replaced my TTL Cookbook with a Cmos cookbook about 30 years ago. I have not used old high power TTL ever since.
Thanks everybody for the info and insights into the 555 ... I do not think the 555 would do the job,
being unstable, rough sounding audio output, need to preamp voltage input greatly ... so I will try to find
another IC that may do the job.
Make a Wien Bridge sinewave oscillator with a dual-Jfet setting its frequency and another Jfet adjusting its maximum output level. It can drive an audio amplifier IC.
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