pulse generator

What's the bias pin? Do you mean pin 5?

I've already talked about that, it will vary the frequency.

Then why not vary pin 5 for frequency, and use the dual diodes w/pins 2 & 6 for duty cycle? I've thought about trying that, but each time I think about it, I just don't think using pin 5 works very well. Course, I've been too lazy to try it.

Edit: The more I think about it, the more I think it should work, depending on how good the timer comparators are.

Like this:

Opps, left out capacitor, but hope you know where I'm going with this.


EDIT: Simulation gave unsatisfactory results. Also shows pin 5 changes duty cycle.

Generally speaking, classical pulse generators had very fast rise- and fall-times. The typical unit had adjustments for pulse frequency (or period), pulse width, rise time and fall time. Positive-going and negative-going outputs were available and the amplitudes on both were adjustable, on older units often going as high as ±80 or 90 volts peak. The units were always oscillators that drove one-shots and the oscillator on some models could be configured for single-pulse or triggered operation.

One of the characteristics of this oscillator/one-shot combination was that the operator was always accidentally setting the oscillator such that it's period was shorter than the pulse. Of course, the result was the the output pulse disappeared since the one-shot was being retriggered before it completed its previous pulse.

Dean Huster said:

Generally speaking, classical pulse generators had very fast rise- and fall-times.

Click to expand...

Yep, usually Schmitt triggers. The rise and fall edges are so fast you have to have a pretty decent scope to measure them.

hero's circuit works well with an NE555.

I used an N-channel MosFet instead of a P-channel type because of generally lower RDS(ON).

Here are the simulation results. (tried with 47nF and 22nF without change of properties, motor model used: 9V/6Ω, load/max torque 50%)

There is a voltage drop of approximately 400mV across the transistor not allowing full speed of the motor. You might use a switch to bypass the transistor for full rpm. (also shown in the schematic)

Boncuk

The drop across the transistor depends on the transistor used.

Have you actually built it or have you just simulated it?

Here's another way to achieve variable frequency and duty cycle.

https://www.electro-tech-online.com/threads/variable-frequency-and-duty-cycle.96824/