Hi guys.
This is part of a segment of a design I came up with using schmitt triggers as relaxation oscillators.
The picture below shows the 4 possible states of the circuit at any given time.
Basically, the left side toggles between 0V and 3V faster than the right. From this, the voltage across C3 changes at different rates given what 'state' the schmitts are in (0,0...0,3...3,0...3,3). This changes the oscillation rate and hence generates two different tones.
The capacitor voltage moves between 0.478V and 2.054V as thats the upper and lower thresholds the schmitt toggles its output.
Basically what I need to do is find the time taken to charge then discharge, with respect to C. From here I can spreadsheet capacitor values and pick one that generates the frequency I desire.
The (0,0) and the (3,3) states are easy because its a simple RC circuit after you combine the parallel resistors.
The (0,3) and the (3,0) states are harder because as Vc goes up, it opens up a potential voltage drop across the other resistor.
This is the formula I derived to find t with respect to C;
Granted the only difference is the direction the 3V comes from for these 2 harder states, I thought I could just swap what i substitue for R1 and R2 around.
When R1 = 3300ohms, R2 = 560ohms....I can solve it.
But when R1 = 560ohms and R2=3300ohms I get a negetive inside my log and cant get any further.
Is there a better way to be trying to calculate these 2 conditions? How can I work out the (0,3) state?
Thanks for any help.
This is part of a segment of a design I came up with using schmitt triggers as relaxation oscillators.
The picture below shows the 4 possible states of the circuit at any given time.
Basically, the left side toggles between 0V and 3V faster than the right. From this, the voltage across C3 changes at different rates given what 'state' the schmitts are in (0,0...0,3...3,0...3,3). This changes the oscillation rate and hence generates two different tones.
The capacitor voltage moves between 0.478V and 2.054V as thats the upper and lower thresholds the schmitt toggles its output.
Basically what I need to do is find the time taken to charge then discharge, with respect to C. From here I can spreadsheet capacitor values and pick one that generates the frequency I desire.
The (0,0) and the (3,3) states are easy because its a simple RC circuit after you combine the parallel resistors.
The (0,3) and the (3,0) states are harder because as Vc goes up, it opens up a potential voltage drop across the other resistor.
This is the formula I derived to find t with respect to C;
Granted the only difference is the direction the 3V comes from for these 2 harder states, I thought I could just swap what i substitue for R1 and R2 around.
When R1 = 3300ohms, R2 = 560ohms....I can solve it.
But when R1 = 560ohms and R2=3300ohms I get a negetive inside my log and cant get any further.
Is there a better way to be trying to calculate these 2 conditions? How can I work out the (0,3) state?
Thanks for any help.