Hey, I liked the 2001 jokes ;-)
Chuck
--- In motm@y..., mark@i... wrote:
>
> I'd thought I'd rephrase my questions, and leave out the silly _2001: A
> Space Odyssey_ jokes, in hope of getting a better response.
>
> I would like to build an edge detecting circuit in order to derive a
> trigger signal from the voltage changes of a stepped waveform. I plan on
> using it with the CV output of a UEG in LOOP ONLY mode with the SLOPE
> switch set to STEP. So it will generate a signal when the voltage changes
> in either direction.
>
> I'm not an EE, but I have a copy of Horowitz & Hill. Based on that text, I
> have pieced together the following ideas for a circuit:
>
> Take the CV output of the UEG, run it through a voltage follower (as not to
> draw too much current), to a differentiator. Figure 4.51 on page 224 looks
> like a cap (C) going into the inverting input of an op-amp, with a resistor
> (R) going from the op-amp's output to the inverting input, and the
> non-inverting input going to ground, such that:
>
> Vout = -RC dVin/dt
>
> Then it says this circuit generally has "problems with noise and
> instabilities at high frequencies because of the op-amp's high gain and,
> internal phase shifts". It shows a new circuit, with high-frequency
> rolloff, in Figure 4.52. Yet it doesn't give a formula in which to
> calculate the component values. Does anyone know how to get this circuit
> in Figure 4.52 so that it will work?? Any other ideas??
>
> Even if I can get the differentiator to work, I would end up with both
> negative and positive voltages. So after this differentiatior, I would
> need an "absolute value circuit" or "active full wave rectifier", I found
> two on page 222.
>
> After that, I need to get this positive voltage up to approximately 5
> volts, with enough current available to be used as a trigger. Is there a
> comparator circuit that anyone would like to recommend?? I'm thinking a
> LM339 with a pullup resistor connected to 5 volts would work.
>
> Do they make comparators that will give a positive output regardless of the
> polarity of the input voltage?? The table in Horowitz & Hill (pp. 584-585)
> leads me to believe that an LM311 can, which would eliminate the need for
> an absolute value circuit. Any ideas??