Pulse Train Circuit

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  • Last Post 19 February 2018
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Zanzal posted this 12 January 2018

I thought I'd share a circuit for generating pulse trains that repeat for a certain duration and frequency. The example is shown in an online circuit simulator and uses two timers. One controls the burst width and burst frequency and the other controls the individual pulses that make up the burst.

You can tinker with the circuit using the links below:

Version 0.2
Removed superfluous AND gate and added a NOR gate to fix error on reset. The extra NOR gate may not be needed for the real circuit. The 555 controlling burst width and frequency was replaced with a square wave source to better illustrate that any square wave source can be used to control the burst width and frequency.

Version 0.1
First version. Had some redundant components that were not needed.

 

 

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Zanzal posted this 19 February 2018

Thanks Chris. I had 10 pcbs made through pcbway for $14 shipped. The other 9 can be used in projects that need to be driven from this signal source so I don't really feel inclined to sell them. When using them that way one doesn't necessarily need to add piano dips or use the long knob pots. ICs can be used without sockets, etc.

If anyone finds a good use for them, feel free to share.

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Chris posted this 18 February 2018

That is Awesome Zanzal - Very nice!

How many boards did you get made?

If you have some spare, and if you like, post details here and if others want to buy, then you can make a little on the side?

This sort of stuff is just fantastic! Others sharing their skills and know how, its great to see! Again, part of the reason we are Light Years Ahead of the others, our excellent Community!

   Chris

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Zanzal posted this 18 February 2018

Finished PCBs arrived. I haven't had a chance to really play around with it too much yet, but so far it looks really nice. Specs should be:

Max load: 25mA (Limited by CD74HC02E output pin)
Max input voltage: 40V
Min input voltage: 5.5V
Reverse polarity protection: up to -24V
No load current draw: < 1.5mA @ 12.5V
Minimum output pulse width at lowest capacitance: 320ns


Important considerations:

  • There is no transistor/resistor or other protection for the output / trigger pins.
  • Only use CMOS NOR chip (CD74HC02)
  • LM358 dual op amp can be substituted with another op amp with similar operating characteristics and pin layout.
  • No indicator LED.
  • The piano dip layout may be a little annoying. In hindsight I should have ensured the same switching layout for both instead SW2 is reversed (not a big deal, it still works).

 

The gerber files and bill of materials are attached in case anyone wants to make one.

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Zanzal posted this 27 January 2018

First PCBs have been ordered. It may be a couple weeks before they arrive and can be tested, but if all goes well, I will make the them available here.

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Chris posted this 24 January 2018

Thanks for sharing Zanzal - This sort of thing is so valuable!

Many have skills in many areas, but not all, some have little Electronics skills, so for all here, this is valuable!

Thank you for sharing!

   Chris

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Zanzal posted this 24 January 2018

Version 0.3.1
Just some small value tweaks and I also labelled the trigger point.

The circuit has been tested on a breadboard and surprisingly it works. Components are:

LM2936Z-5/NOPB Regulator, 2N7000G N-channel mosfet, TLC555 fast low power 555, CD74HC02E quad 2-input NOR gate IC, LM358P op amp

If simulations are correct, it could draw as much as 5mA at very high frequencies, but at the low frequencies I was using it was only 1.6mA (no load) from a 12V battery.

 

 

 

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Zanzal posted this 18 January 2018

Version 0.3
Added an LM358 based PWM to control burst frequency and width, ensures that changing burst frequency does not change burst duty cycle. Optimized for current draw, less than 1ma (not counting power used by ICs). This can increase a bit with higher frequencies. Also the pulses no longer limited to being 50% duty cycle, an on off period can be set using two additional potentiometers. LM358 circuitry is based on the one from ebay that sells for about a dollar.

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Wistiti posted this 13 January 2018

Nice to have you in Zanzal! Thanks for sharing!

Zanzal posted this 12 January 2018

I've updated the circuit. The AND gate was not needed, which is great since adding an IC for a single gate is annoying. The circuit also better shows how you can control burst width and frequency using a signal generator or any square wave source (mind the voltage on the signal source should not exceed the voltage limitation on your NOR gate ic.)

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Chris posted this 12 January 2018

Hey Zanzal, a few minor improvements... 

My Wife, love her to bits, says this to me all the time, "You never have anything finished..." I say to her that I am making improvements, its the next generation...

She shakes her head... I shake mine... 

Point is, its a place to start, a Baseline for the next model!

   Chris

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Zanzal posted this 12 January 2018

Thanks Chris, I haven't had a chance to build the real circuit since I had no logic gates. I just realized there may be a logical error here, but it will be several weeks before I can test it. If it turns out that the function is simply the result of simulator bugs then I'll post a new schematic.

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Chris posted this 12 January 2018

Hey Zanzal - Awesome Thank You!

This circuit and the output it produces has been used by the likes of Stan Meyer and many others - This is a huge benefit to others!

Thank You!

   Chris

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