Pulse Generator Semantics

Thread Starter

StevoKeano

Joined Jan 13, 2024
14
@radiationalert1 require alignment equipment including "A pulse generator capable of producing the following pulses, 100usec, Negative going, 5VDC, 4.49hz" among others.
20240113_143949.jpg
Finishing up the "Monitor 4" kit and unclear what "negative going" pulse looks like. Attached scope of an Arduino 100usec duty cycle pulse.
20240113_153855.jpg
Have an AE20125; but alas, no DC Offset or experience using it ( just built). Please go easy, 1st time posting. Did ask radiationalert1 but nothing yet.
20240113_154401.jpg
 
Last edited by a moderator:

Thread Starter

StevoKeano

Joined Jan 13, 2024
14
@radiationalert1 require alignment equipment including "A pulse generator capable of producing the following pulses, 100usec, Negative going, 5VDC, 4.49hz" among others.
View attachment 312645
Finishing up the "Monitor 4" kit and unclear what "negative going" pulse looks like. Attached scope of an Arduino 100usec duty cycle pulse.
View attachment 312650
Have an AE20125; but alas, no DC Offset or experience using it ( just built). Please go easy, 1st time posting. Did ask radiationalert1 but nothing yet.
View attachment 312651
Found AE20125 DC offset, and generated this "pulse?".20240113_163838.jpg
 

k1ng 1337

Joined Sep 11, 2020
960
Hi, here is a simulation showing the difference between Positive-going Pulse, Negative-going Pulse, Rising Edge and Falling Edge.

The PULSE command for the left circuit simulates a 1s pulse of 0 to +1V with a Rise Time of 1ms and a Fall Time of 1ms after a delay of 3s.

The PULSE command for the right circuit simulates a 1s pulse of 0 to -1V with a Rise Time of 1ms and a Fall Time of 1ms after a delay of 3s.

Notice how both circuits are exactly the same aside from one being +1V and the other -1V. We say the +1V circuit is Positive-going because the voltage is a positive value relative to 0V. Likewise, we say the -1V circuit is Negative-going because the voltage is a negative value relative to 0V.

Make sense?

Untitled.png
 

k1ng 1337

Joined Sep 11, 2020
960
Doesn't your 'negative-going pulse' have mislabelled edges?
Why? A rising edge is representing an increasing voltage. Since 0 to -1V is an increase in voltage potential, it makes more sense to me to call this the rising edge unless we have a system biased towards positive voltages which is not present here.
 

boostbuck

Joined Oct 5, 2017
515
I suppose I would regard a transition from 0 to -1 as a fall in voltage potential. It's just the same as from 1 to 0 but with a different reference point.
 

Thread Starter

StevoKeano

Joined Jan 13, 2024
14
So leading edge, rising potential, negative going, or positive going. Nice semantics. Thanks. Now off to generate negative going 100usec 4.59hz 5vdc pulse.
 

k1ng 1337

Joined Sep 11, 2020
960
I suppose I would regard a transition from 0 to -1 as a fall in voltage potential. It's just the same as from 1 to 0 but with a different reference point.
I don't see how this is a decrease / fall in potential because current increases from 0-1A. This is the same for the positive pulse so the designation of each pair of edges is the same.

So leading edge, rising potential, negative going, or positive going. Nice semantics. Thanks. Now off to generate negative going 100usec 4.59hz 5vdc pulse.
Keep in mind going from +5 to 0V may be regarded as a Negative-going pulse depending on the reference point chosen. This is like reversing the probes on a multimeter, it's the same reading but the signs are reversed.

I'm fairly certain the proper treatment of the term Negative-going is when a signal goes from 0V to some negative value like -1 or -10V. The thing to remember is a voltage is always taken to be the potential difference between two points. Our designations of these terms are arbitrary as long as we stick with the paradigm that 0V is common to all other voltages.

If you are strictly working with positive voltages, then it can be assumed Negative-going means a pulse of +5 to 0V. Eventually you will realize the difference between a positive and negative voltage is simply a reverse in the direction of a current through a load. I can provide a few more simulations to make this clear.
 

boostbuck

Joined Oct 5, 2017
515
I regard a voltage as absolute, irrespective of the direction of current through a load, and the scale of the voltage is defined measured from an agreed reference point ("signal ground"). If I reverse the connections to the load it does not reverse the voltages supplied unless the agreed reference is with respect to the load, which is normally isn't. So in the example from the TS, the supplied signal is normally +5V with respect to the agreed circuit ground, and the pulse is 'negative going' to ground with respect to it's normal state and has a falling leading edge and a rising trailing edge.

It's but an opinion of mine. I'm sure yours is just as valid but holding different definitions certainly make communications clumsy. I'd be interested to be pointed to a more formal definition of these terms.
 

Thread Starter

StevoKeano

Joined Jan 13, 2024
14
Indeed, Distructions say...
A Pulse generator, capable of producing the following pulses, 100 µsec, Negative going, 5 VDC, at 4.49 Hz., 20 μsec, Negative going, 5 VDC, at 43.7 Hz., 200μsec, Negative going, 5 VDC, at 417.8 Hz.

Got any pulse generator in mind I might use?
 

Thread Starter

StevoKeano

Joined Jan 13, 2024
14
Thanks! Specs are as stated by the kit manufacturer... Thanks for the options! may go the DIY route! After today my DS1052E failes to boot. Ugh.
 

k1ng 1337

Joined Sep 11, 2020
960
I regard a voltage as absolute, irrespective of the direction of current through a load, and the scale of the voltage is defined measured from an agreed reference point ("signal ground"). If I reverse the connections to the load it does not reverse the voltages supplied unless the agreed reference is with respect to the load, which is normally isn't. So in the example from the TS, the supplied signal is normally +5V with respect to the agreed circuit ground, and the pulse is 'negative going' to ground with respect to it's normal state and has a falling leading edge and a rising trailing edge.

It's but an opinion of mine. I'm sure yours is just as valid but holding different definitions certainly make communications clumsy. I'd be interested to be pointed to a more formal definition of these terms.
Hmm.. I have to think about it. I'm also interested in the formal definitions which is why I stay away from these kinds of terms. I prefer to say something like: +5V to 0V pulse or +5V to -5V pulse because it is fairly obvious what the intention is.

Indeed, Distructions say...
A Pulse generator, capable of producing the following pulses, 100 µsec, Negative going, 5 VDC, at 4.49 Hz., 20 μsec, Negative going, 5 VDC, at 43.7 Hz., 200μsec, Negative going, 5 VDC, at 417.8 Hz.

Got any pulse generator in mind I might use?
This can be easily done with the trusty ol' 555 timer. I used this calculator to find the component values based on your specs:

NE555 Astable Multivibrator Frequency and Duty Cycle Calculator (daycounter.com)

The box in the first graph is showing the Low Time and the box in the second graph is showing the Period.

Untitled.png
Untitled2.png
Untitled3.png
 

k1ng 1337

Joined Sep 11, 2020
960
A better option would be to use a microcontroller with a quartz crystal. The 555 timer is RC based (a low Q) and each component has a +- manufacture tolerance. These factors may lack the precision you require.

For the example above, simply write a 5V GPIO pin HIGH for 2.393ms and LOW for 0.200ms to achieve the same result. I can provide an Arduino sketch to do this.
 
Top