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Author Topic: RING COUNTER and SEQUENTIAL CIRCUITS  (Read 17765 times)

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I had some time this weekend to try some different methods of building a ring counter from various IC's.

I was successful with 74ACT74's, and 74HC4017 (which I have use for a long time), but I could not figure out how to get a 74HC164 shift register, or a 74hc174 hex F-F to work in a self-running, looped mode.  For the two that didn't work, I was not sure how to start the count or whether to loop the last output back or not.

So, I have placed this thread here for the purpose of sharing practical sequential circuits.
   

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Hi G

I found that Shift registers had too much Jitter and ended up building the attached diagram as a little module, it worked well, i used this for my Spheric build.

EDIT although the circuit shows the chips to be the 'F' variant i found them very power hungry, i used HCT instead.
« Last Edit: 2011-05-31, 14:22:20 by Peterae »
   

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Thanks Peter.   I have found the 74HC74 to work well, and you can access the time between pulses should you need to.

Attached is a self-starting ring counter with a NOR Gate:
   

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5 input NOR gates for above:
   

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Don't use F logic it's a pain in the arse, use anything else LS, HCT or whatever meets your speed requirements.

Have you heard of Potato Logic, it's the same gates as TTL but runs at GHZ speeds, not sure how easy it is to buy though never needed it yet
http://www.potatosemi.com/potatosemiweb/74Logic.html

Look at the specs of this 74G74 it runs faster than 600MHz LOL  :D
http://www.potatosemi.com/potatosemiweb/datasheet/PO74G74A.pdf
   

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Don't use F logic it's a pain in the arse, use anything else LS, HCT or whatever meets your speed requirements.

Why is that?

QUESTIONS:

1. Is the CLR of a SN74AHC174 Hex D-Type F-F tied to Vcc if unused?  (I think so, want to make sure.)

2. Regarding the SN74F260 Dual 5-input NOR Gate, if the second group of 5 gates and output is not used, can I ignore them?

http://www.overunityresearch.com/index.php?topic=2303.20
« Last Edit: 2014-10-24, 21:59:33 by Grumpy »
   

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Quote
1. Is the CLR of a SN74AHC174 Hex D-Type F-F tied to Vcc if unused?  (I think so, want to make sure.)

All Inputs need to be tied appropriately, in the data sheet it is /CLR the bar indicates it is active low, so when tied low then you will clear the Q output to a logic low or 0, so the answer to your question is you must tie it high to disable the clear function.
   

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The F Fast Logic is not so easy to work with especially if you are prototyping on vero, the inputs need to be driven correctly, if you are not careful and have any noise you can destroy them through high current consumption, they can be power hungy, i would advise you to avoid them there are better technologies that are less power hungry, if you must use the F series then read the data sheet very carefully and run them in spec by driving the inputs correctly.
   

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The F Fast Logic is not so easy to work with especially if you are prototyping on vero, the inputs need to be driven correctly, if you are not careful and have any noise you can destroy them through high current consumption, they can be power hungy, i would advise you to avoid them there are better technologies that are less power hungry, if you must use the F series then read the data sheet very carefully and run them in spec by driving the inputs correctly.


What about "S" logic?

There are not a lot of options in a 5-input NOR gate.
   
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I use a 74ls175 flip flop.
   

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Ordered some "S" logic NOR gates:


I have the 175 for the tetra.
   

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What speeds are you aiming for.

Why a 5 Input Nor the circuit you posted only require a 3 input nor, if so i would try ALS
http://www.futurlec.com/74ALS/74ALS27.shtml
   

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I have a ring counter made from a hex D F-F.  To ensure that it starts on it's own a NOR gate is required.  One input for each channel minus 1.  So it has to have at least 5 inputs.

Each F-F output goes to the next stage, to the NOR gate and to an isolation transformer made from a tiny ferrite toroid.  Each isolation transformer activates an avalanche stack at the high side.

I used a 164 shift reg before, but it can't be delayed between the stages, only at the output.  Same with the Johnson counter (4017?).


   

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Ok i understand now G  O0
   

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Is thee anything I need to worry about when connecting various devices together that have separate physical grounds.

What I mean is I have:

1. wall plug -> 5v PS -> controller board -> coils  (trigger Pulses)
2. Wall plug -> freq gen -> controller board (CLK)

Should be fine, right?

Everything else is isolated.
   

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Often-times it is very difficult to predict whether
things will play together nicely or whether you'll
get some weirdness.

Conventional wisdom tells us that, barring any
groundloops, things should go as you hope.

Have you tried it yet?


---------------------------
A man gets depressed, he gets sad, he thinks about quitting and folding, but he never does. He pushes through adversity. - Chad Howse
   

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Interesting you are asking that question G.

You could try measuring from your mains earth connection to the freq gen chassis to see if there is any voltage reading, same with the supply.
   
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Wall supplies are isolated, you would need to connect the grounds together. If I'm not mistaken, anyway.
   

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I had a nasty problem with an ungrounded PS before.  I never did figure out why all of the metal like the pots and heatsink for the regulator chip got such a high charge on them.  It was only while driving a HV supply into a pulser.

My 5v PS is ungrounded.  It's a simple one with a LT regulator and a small transformer,  What is the best way to ground it?  Ground the transformer and the heatsink?  I don;t think I should tie neg to ground, just ground everything else.   It's in a plastic box.
   

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The secondary of the transformer is very unlikely to have leakage to earth, if you want to be sure use a current measuring meter in series with a high value resistor and see if you can measure any AC current, start with a high value resistor and once you are sure there's no leakage current lower the value, if you have even 1mA leakage something is wrong, if there is no leakage then earth the 0V line.

Once earthed be carefull, it's easier to kill yourself with an earth by giving yourself another current path
   
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