single supply op amp relaxtion oscillator

[h1386343]

i try to make relaxation oscillator with a single supply op amp
but i don't find any equation to determine the frequency   

assuming supply is 9V

[Paul Price]

Hint:  A Relaxation Oscillator has two phases to complete one cycle and each cycle takes some time.

Hint: If you call the time it takes for the Relaxation Oscillator output to reach a maximum voltage peak and remain steady T1 and call the time it takes the oscillator to reach a minimum voltage output and maybe remain steady T2, you have a way to determine the Period of oscillation.
Now period, P is the time for one oscillation, and Frequency is 1/P. The period, P= T1+T2 .

Hint2:  If the Relaxation Oscillator has a single capacitor called C in value, then the time it takes to charge the capacitor is proportional to the resistance in series with it to to charge it to a critical charging voltage, and this time is T= some constant value times RC.
 
Hint3:  T1 might be equal to x1*RC and T2 = x2 *RC where x1 and x2 are constants determined by your circuit and usually have values in the range of  >0 to <5 and might even be equal.

Hint4:  The values of any resistors connected to the charging capacitor in a Relaxation Oscillator determine the frequency. Other resistor values may set voltages for the oscillator to reach the Max and Min output amd oscillate without locking up in either the positive or negative excursion of oscillation.

[Paul Price]

Hint: The output frequency may be independent of the supply voltage over a great range of operation.

Hint: A control voltage input may work to determine the time T1 and the time T2, but both will always be the same total= P

P=T1 +T2

Hint: T1 could even be equal to T2.

Hint: The time it takes a capacitor in series with a resistor to reach about 63% of the its maximum charged voltage from an instantaneously stable voltage source  is equal to the value of one times R times C   

Hint:  Any capacitor fed from a fixed voltage source will charge almost to 99% of its final value in the time of 5 times RC.

Hint:  There are critical voltages that cause the Relaxation Oscillator to switch its output from a maximum positive output state to a minimum voltage output state. When this kind of oscillator is working the output may remain stable in either state while the capacitor is charging and then discharging.

Hint: The output of this oscillator may be a type of square wave with two components of its Period, T1 and T2.

Hint: From what I've told you here you can determine the frequency of oscillation.

[h1386343]

sorry but don't get it 

[Paul Price]

You have asked for an equation to determine the frequency and I have given it to you.

[nuhamind2]

Check the voltage of the capacitor with scope. By doing so I think you can intuitively guess how the frequency determined.

[vlf3]

This should help, no intended insult...

http://www.dummies.com/how-to/content/electronics-components-calculate-time-constants.html