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Convert Square Wave Signal to Spike Signal

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WishIknew

New Member
I need to convert a square wave signal to a signal with a spike (not sure what the official term is). Below is a photo of the scope screen with the signal I am looking to convert to (see below).

DSC09753.JPG


I want to convert too look like the signal below.

DSC09758.JPG


If you have any ideas please send them over.

Duane Martin
 

rjenkinsgb

Well-Known Member
Most Helpful Member
An "edge detector"?
A series capacitor in to a full wave rectifier, with a resistor as a load. The time constant of the cap and resistor will define the pulse size.

Or, if it's a logic circuit, an XOR gate with the direct signal to one input, then that also linked by a series resistor and shunt capacitor to the other input.
The gate would give an output at each transition, until the cap charged to the new level and it turned off again.

That may need a gate with schmitt inputs or buffers before it, to handle slowly changing signals. You can make an XOR from the gates in a 4093 schmitt NAND.

There are other ways as well.
 

crutschow

Well-Known Member
Most Helpful Member
So you want a positive pulse (spike) on each transition of the squarewave?
 

WishIknew

New Member
The minimum high voltage is 80mv and the low is 40mv. One positive pulse for every 80mv high pulse of the square wave. The pulse in both pictures is generated by a tonewheel and pickup coil. The rate of the pulse changes with the speed of the tone wheel.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
That will need buffering / amplifying first, before any further processing.
See the second section on this page, the microphone preamp. That should be suitable, with R1 eg. 1K and a 100k preset for Rf, giving a gain anything from 1 to 100.

Follow that with a unity gain inverter; eg. the second half of this circuit using R3, R4 and the opamp, with R3 fed directly from the above opamp output.

Both opamps outputs then feed to two of these so-called "voltage doubler" circuits:

Leave out C1, as you don't want a smoothed output, and join the two outputs together (so RL is shared between the two).

The pulses you get will have a duration based on the time constant of the input capacitor and the load resistor; eg. a 10K load and 47nF input caps to the rectifiers should give good pulses.
 

AnalogKid

Well-Known Member
Most Helpful Member
1. Your scope shots in post #1show output pulses (spikes) at every positive ***and negative*** transition of the input square wave. This is different from what you describe in post #5, so please clarify.

2. Do you want the output to be a spike, or a pulse? A pulse is different from a spike. A pulse has a leading edge, a nominally flat top or a measurable width, and a trailing edge. Usually, a spike has a rapid, straight-line increase for the leading edge up to a point, then a less rapid exponential decrease for the trailing edge. A common description for the width of the spike is the width at 50% of the peak amplitude.

3. What is the desired output pulse amplitude.

4. What is the desired output pulse width?

ak
 
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