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Old April 1st 15, 07:00 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Default "Random" Circuit Needed.

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

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Old April 1st 15, 07:27 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Posts: 2,022
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


---
If you use something like an HC154 with an LFSR driving its address
inputs to generate random one-hots on its outputs, will that work
for you?

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Old April 1st 15, 07:53 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Posts: 2,181
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 13:27:06 -0500, John Fields
wrote:

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


---
If you use something like an HC154 with an LFSR driving its address
inputs to generate random one-hots on its outputs, will that work
for you?


John,

What are you saying... take the outputs of the LFSR broadside to drive
the address lines of the 'HC154?

I think that would do it.

Thanks also to Lasse for the same suggestion.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Old April 1st 15, 08:06 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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First recorded activity by DIYBanter: Feb 2012
Posts: 231
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


Do you want to build hardware, or just Spice this?

LT Spice has random signal generators. You could quantize one of them,
and drive a decoder.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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Old April 1st 15, 08:07 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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First recorded activity by DIYBanter: Sep 2006
Posts: 611
Default "Random" Circuit Needed.

On 04/01/2015 02:00 PM, Jim Thompson wrote:
For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


How random? You could use a 16-bit PRBS made from two HC299 and an
HC86. Feed back Q14 XOR Q13, and tap out four stages to a HC154 demux.
If you need better randomness, use four PRBSes of different length.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net


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Old April 1st 15, 08:08 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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First recorded activity by DIYBanter: Mar 2010
Posts: 2,181
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 12:06:00 -0700, John Larkin
wrote:

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


Do you want to build hardware, or just Spice this?

LT Spice has random signal generators. You could quantize one of them,
and drive a decoder.


"For a simulation situation..." ;-)

John F and Lasse have provided how to do it.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Old April 1st 15, 08:10 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Posts: 2,181
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 11:53:10 -0700, Jim Thompson
wrote:

On Wed, 01 Apr 2015 13:27:06 -0500, John Fields
wrote:

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


---
If you use something like an HC154 with an LFSR driving its address
inputs to generate random one-hots on its outputs, will that work
for you?


John,

What are you saying... take the outputs of the LFSR broadside to drive
the address lines of the 'HC154?

I think that would do it.

Thanks also to Lasse for the same suggestion.

...Jim Thompson


I was puzzling over how to get 0000, but then it dawned... just use an
8-bit LFSR and use the last 4-bits.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Old April 1st 15, 08:14 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Posts: 2,181
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 15:07:54 -0400, Phil Hobbs
wrote:

On 04/01/2015 02:00 PM, Jim Thompson wrote:
For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


How random? You could use a 16-bit PRBS made from two HC299 and an
HC86. Feed back Q14 XOR Q13, and tap out four stages to a HC154 demux.
If you need better randomness, use four PRBSes of different length.

Cheers

Phil Hobbs


I just need semi-random enough to test a fast AGC.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Old April 1st 15, 08:18 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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First recorded activity by DIYBanter: Jul 2006
Posts: 2,022
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 11:53:10 -0700, Jim Thompson
wrote:

On Wed, 01 Apr 2015 13:27:06 -0500, John Fields
wrote:

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson


---
If you use something like an HC154 with an LFSR driving its address
inputs to generate random one-hots on its outputs, will that work
for you?


John,

What are you saying... take the outputs of the LFSR broadside to drive
the address lines of the 'HC154?


---
Yes.
---

I think that would do it.


---
OK :-)
---

Thanks also to Lasse for the same suggestion.


---
He posted earlier than I did, so the "win" is really his.

Also, perhaps not immediately apparent is that he also posted that
the length of the LFSR will determine the repeat of the one-hot
sequence out of the demux.

For example, if you use a maximal length 4 bit LFSR, the sequence
will repeat every 15 clocks, while if you use a maximal length 8 bit
LFSR the sequence will repeat every 255 clocks, and so on...

John Fields
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Old April 1st 15, 09:13 PM posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.basics
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Posts: 2,022
Default "Random" Circuit Needed.

On Wed, 01 Apr 2015 12:10:24 -0700, Jim Thompson
wrote:

On Wed, 01 Apr 2015 11:53:10 -0700, Jim Thompson
wrote:

On Wed, 01 Apr 2015 13:27:06 -0500, John Fields
wrote:

On Wed, 01 Apr 2015 11:00:25 -0700, Jim Thompson
wrote:

For a simulation situation I need a random number generator with a
twist...

What I need to simulate is a "random" selection of one-of-16 outputs.

Clock "speed" is 12.5kHz ;-)

Built of 74HCxx parts is preferred... I have a full ensemble of those
device in my PSpice library.

Thanks in advance.

...Jim Thompson

---
If you use something like an HC154 with an LFSR driving its address
inputs to generate random one-hots on its outputs, will that work
for you?


John,

What are you saying... take the outputs of the LFSR broadside to drive
the address lines of the 'HC154?

I think that would do it.

Thanks also to Lasse for the same suggestion.

...Jim Thompson


I was puzzling over how to get 0000, but then it dawned... just use an
8-bit LFSR and use the last 4-bits.

...Jim Thompson


---
There's really nothing quite like that thrilling flash of discovery,
is there?

If you need 0000 out and you only want to use a 4 bit LFSR, then use
XNOR feedback to force the lockup state to 1111 instead of 0000 and
you'll magically jump over 1111 once per cycle.

If you need an LFSR with a maximal length of 2^n instead of 2^n-1,
then a pulse-stuffer is called for.

If there's any interest I'll post a schematic.


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