2-terminal negative resistance circuits

Bill Sloman wrote:
On Thursday, July 4, 2019 at 11:07:55 PM UTC+2, John Larkin wrote:
On 4 Jul 2019 11:23:58 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Bill Sloman wrote...

[ snip ]

Bill, you're getting awfully snarky in your old age.

He should design something. He might feel better.

I feel fine. I've even designed some stuff recently - though the NSW IEEE July Newsletter is not the kind of electronic design that John Larkin would like us to think that he is thinking of.

Coming home from an excellent dinner in a three star restaurant is an even better way of getting to feel fine, though it doesn't seem to make me any more tolerant of half-baked opinions.

Half-baked opinions are not too tasty....
Click to expand...
 
amdx wrote:
On 7/4/2019 5:57 AM, tabbypurr@gmail.com wrote:
On Thursday, 4 July 2019 11:24:47 UTC+1, Jan Panteltje  wrote:
On a sunny day (Thu, 4 Jul 2019 02:29:38 -0800) it happened Robert Baer
robertbaer@localnet.com> wrote in <ZFjTE.67465$GS1.17679@fx48.iad>:

   2-terminal negative resistance circuits anyone?

   Most especially "Z" types.

   Thanks.

neon bulb

Carbon arc
Fluorescent tube
Pretty much any discharge lamp
Carbon pile with solenoid
Nernst lamp


NT

 Physicist boss was using corundum as an abrasive on PZT8, while
scooping some with an aluminum scoop, he did a measurement, and said
hey, this has negative resistance. I didn't pay much attention, and not
sure what he said is fact, but he was a very intelligent guy.

                            Mikek
Click to expand...
In fact, i have seen a 2-terminal hockey-puck ?regulator? made that
way. Excellent high power beastie.
 
Bill Sloman wrote:
On Thursday, July 4, 2019 at 4:35:04 PM UTC+2, John Larkin wrote:
On Thu, 4 Jul 2019 02:29:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

2-terminal negative resistance circuits anyone?

Most especially "Z" types.

Thanks.

As a college ee project, I built a 2-terminal negative resistance box,
with an opamp and a couple of 9 volt batteries. If you plug in a
negative value for R into the common RC and RLC circuits, the math
still works and the waveforms are radical.

I don't think my instructor understood it.

One might suspect that he understood it better than you did, and consequently wasn't giving you the sort of postive feedback that you seem expect from all your interactions.

They tended to not understand a lot of things that I did. That's another discussion.

Then again, neither do you, and you aren't great at discussion - if you aren't getting praised, you stop listening.

Would that be an example of negative resistance?
Click to expand...
 
On a sunny day (Fri, 5 Jul 2019 11:34:31 -0800) it happened Robert Baer
<robertbaer@localnet.com> wrote in <NKMTE.111392$xm4.49009@fx45.iad>:

Jan Panteltje wrote:
On a sunny day (Thu, 4 Jul 2019 02:29:38 -0800) it happened Robert Baer
robertbaer@localnet.com> wrote in <ZFjTE.67465$GS1.17679@fx48.iad>:

2-terminal negative resistance circuits anyone?

Most especially "Z" types.

Thanks.

neon bulb

Neon bulb more like it;
Click to expand...

After posting that neon bulb remark I realized it is not negative resistance AFAIK,
as its resistance suddenly DECREASES when the voltage across it rises.
The tunnel diode exhibits true negative resistance, as do some transistor
circuits discussed elsewhere.


not a circuit but is (mostly) N-type.
Perhaps with some care, one can extract the negative resistance
avalanche-type characteristics.

In any case, is there a SPICE model?
Click to expand...

I dunno, have only used chili lately.
 
Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie. What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.




One trannny:
0 V +
|
___ |________
| | |
R1 | |
| |/ c |
|---- -| |
| |\|e R3
--- | |
\ / > |----
--- LED R2
| |
--------
|
0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current through R2 + R3.
Click to expand...
Yes, it is not linear, but nowhere near negative resistance.
Do a Spice and you will see how lame it is in action.
 
o pere o wrote:
On 4/7/19 12:29, Robert Baer wrote:
   2-terminal negative resistance circuits anyone?

   Most especially "Z" types.

   Thanks.

Cross-coupled transistor pair.

Pere
Sorry, do not see it. How about a SPICE to show it?
Click to expand...

Thanks.
 
Jan Panteltje wrote:
On a sunny day (Fri, 5 Jul 2019 13:22:44 +0200) it happened Arie de Muynck
no.spam@no.spam.org> wrote in <5d1f3304$0$22349$e4fe514c@news.xs4all.nl>:

On 2019-07-05 12:06, Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie. What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.


One trannny:
0 V +
|
___ |________
| | |
R1 | |
| |/ c |
|---- -| |
| |\|e R3
--- | |
\ / > |----
--- LED R2
| |
--------
|
0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current through R2 + R3.

Very nice idea too. Reminds me of the SOA foldback in PSU and audio
output amplifier circuits. Problem for me would be the high remaining
current through R3, there is no current gain in that path like with the
BJE + JFET circuit. I need a high (inverse) current ratio between lo and
high voltage load.

Yes, but then again an Esaki (tunnel) diode also has high remaining current,
it just decreases a bit at some point.
He did not ask for 'linear' :)

BTW - running out of pencils?

No, but this circuit is so simple that ASCII art will do.
It also better preserved as web links may come and go as servers do.
Click to expand...
But if the sun has a BIG corona fart, the whole electrical system in
the world goes POP and you will need those pencils (and paper).
Real time solid-state graphics..
 
On Fri, 5 Jul 2019 12:40:19 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

piglet wrote:
On 04/07/2019 11:29 am, Robert Baer wrote:
   2-terminal negative resistance circuits anyone?

   Most especially "Z" types.

   Thanks.

Please what is meant by "Z type" ?

piglet

The I/V plot looks like a "Z".
For a real example, take any greater-than 7V zener or any silicon PNP
or NPN low signal transistor EB junction; run curve from zero to 10mA
and you are bound to see the resulting trash.
Some are very noisy.

Thanks.
Click to expand...

Zeners will oscillate in an RC circuit at low current. It is very
noisy.

https://www.dropbox.com/s/z6ozl646hfnbb2q/Zener_Noise.pdf?raw=1




--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Fri, 5 Jul 2019 12:26:12 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

Bill Sloman wrote:
On Thursday, July 4, 2019 at 11:07:55 PM UTC+2, John Larkin wrote:
On 4 Jul 2019 11:23:58 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

Bill Sloman wrote...

[ snip ]

Bill, you're getting awfully snarky in your old age.

He should design something. He might feel better.

I feel fine. I've even designed some stuff recently - though the NSW IEEE July Newsletter is not the kind of electronic design that John Larkin would like us to think that he is thinking of.

Coming home from an excellent dinner in a three star restaurant is an even better way of getting to feel fine, though it doesn't seem to make me any more tolerant of half-baked opinions.

Half-baked opinions are not too tasty....
Click to expand...

It's easy to avoid having silly ideas: never have ideas.


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Thu, 04 Jul 2019 20:09:15 -0500, amdx wrote:

Maybe you did, but I see by your responses to John's posts, you are
very jealous of what he does.

Mikek
Click to expand...

'Envious and resentful' pretty much covers it.



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.
 
John Larkin wrote...
Zeners will oscillate in an RC circuit at low current.
It is very noisy.

https://www.dropbox.com/s/z6ozl646hfnbb2q/Zener_Noise.pdf?raw=1
Click to expand...

Yessir, Tony Williams and I covered that here in depth, about
25 years ago, lots of 500MHZ scope measurements and drawings.
Many physics papers from early 60s, but w/o high-speed scopes.
Unfortunately the files are somehow missing from my computer.


--
Thanks,
- Win
 
On Fri, 5 Jul 2019 21:43:31 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Thu, 04 Jul 2019 20:09:15 -0500, amdx wrote:

Maybe you did, but I see by your responses to John's posts, you are
very jealous of what he does.

Mikek

'Envious and resentful' pretty much covers it.
Click to expand...

That sums up "leftism" pretty well.
 
On a sunny day (Fri, 5 Jul 2019 13:07:24 -0800) it happened Robert Baer
<robertbaer@localnet.com> wrote in <S5OTE.8985$uX3.2752@fx27.iad>:

Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie. What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.




One trannny:
0 V +
|
___ |________
| | |
R1 | |
| |/ c |
|---- -| |
| |\|e R3
--- | |
\ / > |----
--- LED R2
| |
--------
|
0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current through R2 + R3.



Yes, it is not linear, but nowhere near negative resistance.
Do a Spice and you will see how lame it is in action.
Click to expand...

Thank you for pointing out my error.
I did try it in Ltspice, and indeed you are 100% right.
Tried to fix it by changing some component values and even using a zener, but no success.
Your incredible wizdom rules again.
My hat off!
Wonder if I had too much sun or too little 'tronics last week,
could well be, big festivities going on here all day.

Could also be some basic units changed over time due to dark matter and dark force.

I also had the idea to do it with a PIC and one transistor, I am sure that will work,
but slow.
ADC -> software -> DAC -> tranny to short the supply.
:)
 
On 06/07/2019 8:13 am, Jan Panteltje wrote:
On a sunny day (Fri, 5 Jul 2019 13:07:24 -0800) it happened Robert Baer
robertbaer@localnet.com> wrote in <S5OTE.8985$uX3.2752@fx27.iad>:

Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie. What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.




One trannny:
0 V +
|
___ |________
| | |
R1 | |
| |/ c |
|---- -| |
| |\|e R3
--- | |
\ / > |----
--- LED R2
| |
--------
|
0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current through R2 + R3.



Yes, it is not linear, but nowhere near negative resistance.
Do a Spice and you will see how lame it is in action.

Thank you for pointing out my error.
I did try it in Ltspice, and indeed you are 100% right.
Tried to fix it by changing some component values and even using a zener, but no success.
Your incredible wizdom rules again.
My hat off!
Wonder if I had too much sun or too little 'tronics last week,
could well be, big festivities going on here all day.

Could also be some basic units changed over time due to dark matter and dark force.

I also had the idea to do it with a PIC and one transistor, I am sure that will work,
but slow.
ADC -> software -> DAC -> tranny to short the supply.
:)
Click to expand...

Also easy with two BJTs ...

Version 4
SHEET 1 880 680
WIRE -128 -112 -368 -112
WIRE 48 -112 -128 -112
WIRE 176 -112 48 -112
WIRE -368 -48 -368 -112
WIRE 48 0 48 -112
WIRE 176 0 176 -112
WIRE -128 64 -128 -112
WIRE 176 112 176 80
WIRE 176 112 -64 112
WIRE -368 144 -368 32
WIRE 176 160 176 112
WIRE -128 208 -128 160
WIRE -64 208 -128 208
WIRE 48 208 48 80
WIRE 48 208 16 208
WIRE 112 208 48 208
WIRE -128 240 -128 208
WIRE -368 352 -368 224
WIRE -128 352 -128 320
WIRE -128 352 -368 352
WIRE 176 352 176 256
WIRE 176 352 -128 352
WIRE -368 384 -368 352
FLAG -368 384 0
SYMBOL voltage -368 128 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 20 0 1m)
SYMBOL npn 112 160 R0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL npn -64 64 M0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL res 160 -16 R0
SYMATTR InstName R2
SYMATTR Value 300k
SYMBOL res 32 -16 R0
SYMATTR InstName R6
SYMATTR Value 300k
SYMBOL res -144 224 R0
SYMATTR InstName R7
SYMATTR Value 200
SYMBOL res 32 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -384 -64 R0
SYMATTR InstName R1
SYMATTR Value 1
TEXT -272 416 Left 2 !.tran 1m


piglet
 
On 06/07/2019 2:04 am, Winfield Hill wrote:
John Larkin wrote...

Zeners will oscillate in an RC circuit at low current.
It is very noisy.

https://www.dropbox.com/s/z6ozl646hfnbb2q/Zener_Noise.pdf?raw=1

Yessir, Tony Williams and I covered that here in depth, about
25 years ago, lots of 500MHZ scope measurements and drawings.
Many physics papers from early 60s, but w/o high-speed scopes.
Unfortunately the files are somehow missing from my computer.
Click to expand...

More fun stuff ...

<http://www.vk2zay.net/article/157>

piglet
 
On a sunny day (Sat, 6 Jul 2019 15:39:16 +0100) it happened piglet
<erichpwagner@hotmail.com> wrote in <qfqbqm$23d$1@dont-email.me>:

On 06/07/2019 8:13 am, Jan Panteltje wrote:
On a sunny day (Fri, 5 Jul 2019 13:07:24 -0800) it happened Robert Baer
robertbaer@localnet.com> wrote in <S5OTE.8985$uX3.2752@fx27.iad>:

Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie. What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.




One trannny:
0 V +
|
___ |________
| | |
R1 | |
| |/ c |
|---- -| |
| |\|e R3
--- | |
\ / > |----
--- LED R2
| |
--------
|
0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current through R2 + R3.



Yes, it is not linear, but nowhere near negative resistance.
Do a Spice and you will see how lame it is in action.

Thank you for pointing out my error.
I did try it in Ltspice, and indeed you are 100% right.
Tried to fix it by changing some component values and even using a zener, but no success.
Your incredible wizdom rules again.
My hat off!
Wonder if I had too much sun or too little 'tronics last week,
could well be, big festivities going on here all day.

Could also be some basic units changed over time due to dark matter and dark force.

I also had the idea to do it with a PIC and one transistor, I am sure that will work,
but slow.
ADC -> software -> DAC -> tranny to short the supply.
:)



Also easy with two BJTs ...

Version 4
SHEET 1 880 680
WIRE -128 -112 -368 -112
WIRE 48 -112 -128 -112
WIRE 176 -112 48 -112
WIRE -368 -48 -368 -112
WIRE 48 0 48 -112
WIRE 176 0 176 -112
WIRE -128 64 -128 -112
WIRE 176 112 176 80
WIRE 176 112 -64 112
WIRE -368 144 -368 32
WIRE 176 160 176 112
WIRE -128 208 -128 160
WIRE -64 208 -128 208
WIRE 48 208 48 80
WIRE 48 208 16 208
WIRE 112 208 48 208
WIRE -128 240 -128 208
WIRE -368 352 -368 224
WIRE -128 352 -128 320
WIRE -128 352 -368 352
WIRE 176 352 176 256
WIRE 176 352 -128 352
WIRE -368 384 -368 352
FLAG -368 384 0
SYMBOL voltage -368 128 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 20 0 1m)
SYMBOL npn 112 160 R0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL npn -64 64 M0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL res 160 -16 R0
SYMATTR InstName R2
SYMATTR Value 300k
SYMBOL res 32 -16 R0
SYMATTR InstName R6
SYMATTR Value 300k
SYMBOL res -144 224 R0
SYMATTR InstName R7
SYMATTR Value 200
SYMBOL res 32 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -384 -64 R0
SYMATTR InstName R1
SYMATTR Value 1
TEXT -272 416 Left 2 !.tran 1m


piglet
Click to expand...

http://panteltje.com/pub/neg_res2.gif
OK, as the voltage rises Q2 starts conducting and switches the load formed by Q1 off.
?
 
piglet wrote:
On 06/07/2019 2:04 am, Winfield Hill wrote:
John Larkin wrote...

Zeners will oscillate in an RC circuit at low current.
It is very noisy.

https://www.dropbox.com/s/z6ozl646hfnbb2q/Zener_Noise.pdf?raw=1

  Yessir, Tony Williams and I covered that here in depth, about
  25 years ago, lots of 500MHZ scope measurements and drawings.
  Many physics papers from early 60s, but w/o high-speed scopes.
  Unfortunately the files are somehow missing from my computer.



More fun stuff ...

http://www.vk2zay.net/article/157

piglet
Very well done write-up.
Click to expand...
 
piglet wrote:
On 06/07/2019 8:13 am, Jan Panteltje wrote:
On a sunny day (Fri, 5 Jul 2019 13:07:24 -0800) it happened Robert Baer
robertbaer@localnet.com> wrote in <S5OTE.8985$uX3.2752@fx27.iad>:

Jan Panteltje wrote:
On a sunny day (5 Jul 2019 02:30:02 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qfn5aq0g8p@drn.newsguy.com>:

Arie de Muynck wrote...

On 2019-07-05 09:09, piglet wrote:
On 04/07/2019 10:43 pm, Dave Platt wrote:

Lambda diode (e.g. two JFETs).

Or indeed one fet and one bjt.

Like  https://w3jdr.wordpress.com/lambda-diode-experiments/

Nice circuit! Why isn't that in the AoE?
(at least not in the index)

Nice idea, Arie.   What can you do with it?

We like depletion devices, whether JFETs or MOSFETs.
But the -Vgs curve isn't specified or very dependable.




One trannny:
        0 V +
        |
    ___ |________
   |        |    |
   R1       |    |
   |      |/ c   |
   |---- -|      |
   |      |\|e   R3
---       |    |
\ / >     |----
--- LED   R2
   |        |
    --------
       |
       0 V -

Z1 1.5V LED
R1 10k
R2 1k
R3 10k



At low voltages circuit conducts a lot via transistor and R2,
tranny basically shorts R3.

When V goes high at some point (about 10 V) emitter is lifted bove
VZ1 - Vbe,
Ic drops to zero, only current left via R1 and LED plus current
through R2 + R3.



   Yes, it is not linear, but nowhere near negative resistance.
   Do a Spice and you will see how lame it is in action.

Thank you for pointing out my error.
I did try it in Ltspice, and indeed you are 100% right.
Tried to fix it by changing some component values and even using a
zener, but no success.
Your incredible wizdom rules again.
My hat off!
Wonder if I had too much sun or too little 'tronics last week,
could well be, big festivities going on here all day.

Could also be some basic units changed over time due to dark matter
and dark force.

I also had the idea to do it with a PIC and one transistor, I am sure
that will work,
but slow.
ADC -> software -> DAC -> tranny to short the supply.
:)



Also easy with two BJTs ...

Version 4
SHEET 1 880 680
WIRE -128 -112 -368 -112
WIRE 48 -112 -128 -112
WIRE 176 -112 48 -112
WIRE -368 -48 -368 -112
WIRE 48 0 48 -112
WIRE 176 0 176 -112
WIRE -128 64 -128 -112
WIRE 176 112 176 80
WIRE 176 112 -64 112
WIRE -368 144 -368 32
WIRE 176 160 176 112
WIRE -128 208 -128 160
WIRE -64 208 -128 208
WIRE 48 208 48 80
WIRE 48 208 16 208
WIRE 112 208 48 208
WIRE -128 240 -128 208
WIRE -368 352 -368 224
WIRE -128 352 -128 320
WIRE -128 352 -368 352
WIRE 176 352 176 256
WIRE 176 352 -128 352
WIRE -368 384 -368 352
FLAG -368 384 0
SYMBOL voltage -368 128 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 20 0 1m)
SYMBOL npn 112 160 R0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL npn -64 64 M0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL res 160 -16 R0
SYMATTR InstName R2
SYMATTR Value 300k
SYMBOL res 32 -16 R0
SYMATTR InstName R6
SYMATTR Value 300k
SYMBOL res -144 224 R0
SYMATTR InstName R7
SYMATTR Value 200
SYMBOL res 32 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -384 -64 R0
SYMATTR InstName R1
SYMATTR Value 1
TEXT -272 416 Left 2 !.tran 1m


piglet

Excellent!
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