OT: Does anyone have a good, simple random noise generator?

Tony Rolando wrote:

"Steve Jacobson" <stevelists@jjworld.com> wrote in message

news:c16i94trmro9sh8rl01es6maubk9v9fump@4ax.com...

On Tue, 05 Aug 2008 23:07:28 -0400, Steve Jacobson <stevelists@jjworld.com>

wrote:

 

On Tue, 05 Aug 2008 17:44:33 -0700, Gary Gofstein

<ggofstein@lbl_nospam.gov>

wrote:

 

just reverse bias the base emmitter junction of any normal transistor,

NPN breaks down at about 7V. don't connect the collector. the transistor

will be useless for any other purpose after this, it will appear to work

but detailed measurements will show it is out of spec, so throw it away

if you decide not to use it. 1ma is plenty of current. ac couple the

transistor voltage to an op amp and voila! true analog white noise.

 

Gary,

 

What you are saying is to connect the base-emitter junction of an NPN

transistor

to a source greater than 7V.  Connect the base to +7V and the emitter

to -7V.

Ground the base and take the white noise off the emitter (coupled with a

cap).

Is this correct?  What noise voltage should I expect?

 

Thanks for your help.  I hope I don't appear too dense.

 

I will be running the thing at 9V.  Should I be using a current limiting

resistor?  Also, what would be a good NPN transistor?

 

Steve

 

A BC550 is a good place to start. Grab a handful, and select for highest

noise. I have used 2N3904 as well.

 

However, as Gary wrote make sure it doesn't end up back in the parts

bin. Snipping off the collector lead or tab would be one way, or paint

on some gross color (I've used some of my wife's nail polish for that

but don't tell her ...). If it does end up back in the bin that would be

a perfect recipe for drustrations months down the road.

--

Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.

Use another domain or send PM.

Tony Rolando wrote:

"Steve Jacobson" <stevelists@jjworld.com> wrote in message

news:c16i94trmro9sh8rl01es6maubk9v9fump@4ax.com...

On Tue, 05 Aug 2008 23:07:28 -0400, Steve Jacobson <stevelists@jjworld.com>

wrote:

 

On Tue, 05 Aug 2008 17:44:33 -0700, Gary Gofstein

<ggofstein@lbl_nospam.gov>

wrote:

 

just reverse bias the base emmitter junction of any normal transistor,

NPN breaks down at about 7V. don't connect the collector. the transistor

will be useless for any other purpose after this, it will appear to work

but detailed measurements will show it is out of spec, so throw it away

if you decide not to use it. 1ma is plenty of current. ac couple the

transistor voltage to an op amp and voila! true analog white noise.

 

Gary,

 

What you are saying is to connect the base-emitter junction of an NPN

transistor

to a source greater than 7V.  Connect the base to +7V and the emitter

to -7V.

Ground the base and take the white noise off the emitter (coupled with a

cap).

Is this correct?  What noise voltage should I expect?

 

Thanks for your help.  I hope I don't appear too dense.

 

I will be running the thing at 9V.  Should I be using a current limiting

resistor?  Also, what would be a good NPN transistor?

 

Steve

 

A BC550 is a good place to start. Grab a handful, and select for highest

noise. I have used 2N3904 as well.

 

However, as Gary wrote make sure it doesn't end up back in the parts

bin. Snipping off the collector lead or tab would be one way, or paint

on some gross color (I've used some of my wife's nail polish for that

but don't tell her ...). If it does end up back in the bin that would be

a perfect recipe for drustrations months down the road.

--

Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.

Use another domain or send PM.