# How about it? Experiments of the third kind , take 999999.

Started by April 1, 2012
```How about it? Experiments of the third kind , take 999999.
Update
Hotplate design,
stabilizing the heater MOSFET

http://panteltje.com/pub/thermos_box_mounting_plus_heater_circuit_diagram_IMG_3415.JPG
shows the quick sketch diagram of the MOSFET driver.
The idea is that the current through the MOSFET is exactly proportional to the input voltage.
As we all know, MOSFETs like to do their thing too,
and in such a configuration like to sing (oscillate).
And so also this circuit.

Playing with it and the oscilloscope a bit did lead to this very quiet circuit,
that within a fraction of a millivolt has the MOSFET drain current follow the input.
There were 2 issues here, 1) MOSFET likes to oscillate, and 2) opamp too.
So sort of separating both from each other worked.

+4V
R1                                                |
470k           +                                   |------
---===--------------|\        100k       1k       |---       |
|         |        - | >-------===--------===----| |<--      === 1u
control-   ===      ---|/              |             |---|      |
voltage     | 1u   |                  ===        IRLZ34N |     ///
0 to +1 V   | C1   |                   | 1u       on     |
|        ///     |  TCL274          ///       hotplate |
///               |                           as heater | about 300 mA
-------------------------------------|
|
[ ] 3.3 Ohm
|
///

Having a linear relationship between the control voltage and the output current (power) makes
the software control loop simpler.
Why 1 uF everywhere? I bought a bag of 100.
The 470 K is just for test, this will come from the PIC PWM,
R1 C1 is the lowpass.
100 k and 1k are nice round values.
The 3.3 Ohm was calculated using Ohm law.
The rest ... anyways we need no speed, nowhere in the year long project,
Even outside the black box the hotplate, and so the parts on it, easily meets target
temperature of 40C with about 1,3 W input.
Should be way less watts with it in the black box and thermally insulated on top of that.
As stated before, there will be a 1N4148 diode mounted to the hotplate as temperature sensor.
A PIC microcomputer will do the control loop in software.
Time for pizza (heater is still running).

```
```Try a cap from op-amp output to -input, 100pF is enough.  Add a series 10k
resistor between this node (-in with cap) and the shunt resistor, so the cap
has something to work into.  Get rid of the 100k series resistor and 1uF
filter cap.

As shown, it'll something between oscillate and motorboat, depending on the
position of the planets.  The op-amp is an integrator with 90 degree phase
shift, and the RC following it does the same (for a more limited range of
frequencies).  180 degree phase shift at most any frequency means you're
guaranteed to oscillate somewhere.

You might consider making both series input resistors (the 470k control
voltage filter and the shunt voltage feedback) the same value (100k?) so the
input bias (if any) generates a matching offset on both inputs.  As a CMOS
amp, offset won't be the greatest (a few mV, plus input offset bias), but if
this is within a temperature control loop, offset and 1/f noise won't be a
problem.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:jl9spn\$igi\$1@news.albasani.net...
> How about it? Experiments of the third kind , take 999999.
> Update
>  Hotplate design,
>     stabilizing the heater MOSFET
>
> http://panteltje.com/pub/thermos_box_mounting_plus_heater_circuit_diagram_IMG_3415.JPG
> shows the quick sketch diagram of the MOSFET driver.
> The idea is that the current through the MOSFET is exactly proportional to
> the input voltage.
> As we all know, MOSFETs like to do their thing too,
> and in such a configuration like to sing (oscillate).
> And so also this circuit.
>
> Playing with it and the oscilloscope a bit did lead to this very quiet
> circuit,
> that within a fraction of a millivolt has the MOSFET drain current follow
> the input.
> There were 2 issues here, 1) MOSFET likes to oscillate, and 2) opamp too.
> So sort of separating both from each other worked.
>
>                                                        +4V
>       R1                                                |
>      470k           +                                   |------
>   ---===--------------|\        100k       1k       |---       |
>  |         |        - | >-------===--------===----| |<--      === 1u
> control-   ===      ---|/              |             |---|      |
> voltage     | 1u   |                  ===        IRLZ34N |     ///
> 0 to +1 V   | C1   |                   | 1u       on     |
>  |        ///     |  TCL274          ///       hotplate |
> ///               |                           as heater | about 300 mA
>                    -------------------------------------|
>                                                         |
>                                                        [ ] 3.3 Ohm
>                                                         |
>                                                        ///
>
>
> Having a linear relationship between the control voltage and the output
> current (power) makes
> the software control loop simpler.
> Why 1 uF everywhere? I bought a bag of 100.
> The 470 K is just for test, this will come from the PIC PWM,
> R1 C1 is the lowpass.
> 100 k and 1k are nice round values.
> The 3.3 Ohm was calculated using Ohm law.
> The rest ... anyways we need no speed, nowhere in the year long project,
> Even outside the black box the hotplate, and so the parts on it, easily
> meets target
> temperature of 40C with about 1,3 W input.
> Should be way less watts with it in the black box and thermally insulated
> on top of that.
> As stated before, there will be a 1N4148 diode mounted to the hotplate as
> temperature sensor.
> A PIC microcomputer will do the control loop in software.
> Time for pizza (heater is still running).
>

```
```On a sunny day (Sun, 1 Apr 2012 10:48:46 -0500) it happened "Tim Williams"
<tmoranwms@gmail.com> wrote in <jl9tcl\$ju8\$1@dont-email.me>:

>Try a cap from op-amp output to -input, 100pF is enough.  Add a series 10k
>resistor between this node (-in with cap) and the shunt resistor, so the cap
>has something to work into.  Get rid of the 100k series resistor and 1uF
>filter cap.

I have tried several configurations, of course the first one that came to mind
is 'integrator' but I had problems with huge oscillation at some input voltages.
After many test I settled for this, as I cannot get it unstable in any way.
I reduced the source resistor to 1.1 Ohm (2 x 2.2 parallel) to get more
of the generated heat into the hotplate.

>As shown, it'll something between oscillate and motorboat, depending on the
>position of the planets.

The planets seemed favorable today, you will have to show the math why these
should influence - and in what way- the circuit.
I have read about dark energy, but am not that much of a believer,
especially not if it interacts with the electrons in this circuit.
Once someone told be he had a system for the stock market,
and in that system you should buy if this planet went up and the other down,
Why not this planet down and the other up?
That shorted his neural net enough to drop the idea...

>The op-amp is an integrator with 90 degree phase
>shift, and the RC following it does the same (for a more limited range of
>frequencies).  180 degree phase shift at most any frequency means you're
>guaranteed to oscillate somewhere.

The 1k is just a gate resistor to stop the MOSFET from interfering with local FM
and short wave, the 100k isolates the rather low output impedance from
whatever the MOSFET wants to put out on its gate, it is basically a 2 way 'T' filter.

>You might consider making both series input resistors (the 470k control
>voltage filter and the shunt voltage feedback) the same value (100k?) so the
>input bias (if any) generates a matching offset on both inputs.  As a CMOS
>amp, offset won't be the greatest (a few mV, plus input offset bias), but if
>this is within a temperature control loop, offset and 1/f noise won't be a
>problem.

The circuit is now like this:
PIC runs on 3V supply, and the PWM switches between 0 and 3V.
With an 1.1 Ohm resistor for 330 mA max (for now, based on previous plastic box
burning test) no more than 600 mV should be at the + input of the TCL274,
making 330 mV about mid range (it can become -5 &#2013266096;C).
This requires a voltage divider of ratio of .6 to (3 - .6) makes .6 to 2.4,
and to not load that opamp I have now 470 k to the PIC PWM output and 120 k to ground,
normal E series, high values preferred so I can use my 1 uF caps.

+4 V
R1                                                |
470k            +                                  |------
---===---------------|\        100k       1k       |---       |
|        |    |     - | >-------===--------===----| |<--      === 1u
0-3V     [ ]  ===    --|/              |             |---|      |
PWM       |    | 1u |                 ===        IRLZ34N |     ///
from PIC  ///   |C1  |                  | 1u       on     |
|      120k  ///   | TCL274          ///       hotplate |
///                 |                          as heater | about 300 mA
------------------------------------|
|
[ ] 1.1 Ohm
|
///
These are actually nice opamps, very low offset, typical about a mV,
I measure less, even lower offset drift, 1.8 uV (micro volt) per degree C.
And works all the way to -.2 V common mode range (but not very high upwards).
As in these one supply circuits, having the 0 V as reference is nice.
I will take some peculiarities, already I am having great fun with it.
The opamp output voltage range detoriates fast with any load (say 5 mA).

```
```No, like this.
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Current_Sink.png
It is easy to show the speed, stability, accuracy and phase margin are
greatly improved.  If you cannot show why this is better than the circuit
you've drawn, you shouldn't be working with op-amps at all, do it in
software.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:jlaabb\$gek\$1@news.albasani.net...
> On a sunny day (Sun, 1 Apr 2012 10:48:46 -0500) it happened "Tim Williams"
> <tmoranwms@gmail.com> wrote in <jl9tcl\$ju8\$1@dont-email.me>:
>
>>Try a cap from op-amp output to -input, 100pF is enough.  Add a series 10k
>>resistor between this node (-in with cap) and the shunt resistor, so the
>>cap
>>has something to work into.  Get rid of the 100k series resistor and 1uF
>>filter cap.
>
> I have tried several configurations, of course the first one that came to
> mind
> is 'integrator' but I had problems with huge oscillation at some input
> voltages.
> After many test I settled for this, as I cannot get it unstable in any
> way.
> I reduced the source resistor to 1.1 Ohm (2 x 2.2 parallel) to get more
> of the generated heat into the hotplate.
>
>>As shown, it'll something between oscillate and motorboat, depending on
>>the
>>position of the planets.
>
> The planets seemed favorable today, you will have to show the math why
> these
> should influence - and in what way- the circuit.
> I have read about dark energy, but am not that much of a believer,
> especially not if it interacts with the electrons in this circuit.
> Once someone told be he had a system for the stock market,
> and in that system you should buy if this planet went up and the other
> down,
> Why not this planet down and the other up?
> That shorted his neural net enough to drop the idea...
>
>
>>The op-amp is an integrator with 90 degree phase
>>shift, and the RC following it does the same (for a more limited range of
>>frequencies).  180 degree phase shift at most any frequency means you're
>>guaranteed to oscillate somewhere.
>
> The 1k is just a gate resistor to stop the MOSFET from interfering with
> local FM
> and short wave, the 100k isolates the rather low output impedance from
> whatever the MOSFET wants to put out on its gate, it is basically a 2 way
> 'T' filter.
>
>
>>You might consider making both series input resistors (the 470k control
>>voltage filter and the shunt voltage feedback) the same value (100k?) so
>>the
>>input bias (if any) generates a matching offset on both inputs.  As a CMOS
>>amp, offset won't be the greatest (a few mV, plus input offset bias), but
>>if
>>this is within a temperature control loop, offset and 1/f noise won't be a
>>problem.
>
> The circuit is now like this:
> PIC runs on 3V supply, and the PWM switches between 0 and 3V.
> With an 1.1 Ohm resistor for 330 mA max (for now, based on previous
> plastic box
> burning test) no more than 600 mV should be at the + input of the TCL274,
> making 330 mV about mid range (it can become -5 &#2013266096;C).
> This requires a voltage divider of ratio of .6 to (3 - .6) makes .6 to
> 2.4,
> and to not load that opamp I have now 470 k to the PIC PWM output and 120
> k to ground,
> normal E series, high values preferred so I can use my 1 uF caps.
>
>                                                        +4 V
>       R1                                                |
>      470k            +                                  |------
>   ---===---------------|\        100k       1k       |---       |
>  |        |    |     - | >-------===--------===----| |<--      === 1u
> 0-3V     [ ]  ===    --|/              |             |---|      |
> PWM       |    | 1u |                 ===        IRLZ34N |     ///
> from PIC  ///   |C1  |                  | 1u       on     |
>  |      120k  ///   | TCL274          ///       hotplate |
> ///                 |                          as heater | about 300 mA
>                      ------------------------------------|
>                                                          |
>                                                         [ ] 1.1 Ohm
>                                                          |
>                                                         ///
> These are actually nice opamps, very low offset, typical about a mV,
> I measure less, even lower offset drift, 1.8 uV (micro volt) per degree C.
> And works all the way to -.2 V common mode range (but not very high
> upwards).
> As in these one supply circuits, having the 0 V as reference is nice.
> I will take some peculiarities, already I am having great fun with it.
> The opamp output voltage range detoriates fast with any load (say 5 mA).
>

```
```On a sunny day (Sun, 1 Apr 2012 15:12:05 -0500) it happened "Tim Williams"
<tmoranwms@gmail.com> wrote in <jlacqc\$6pj\$1@dont-email.me>:

>No, like this.
>http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Current_Sink.png

Yes Tim, but that is basically an integrator, as  I mentioned.

>It is easy to show the speed, stability, accuracy and phase margin are
>greatly improved.  If you cannot show why this is better than the circuit
>you've drawn, you shouldn't be working with op-amps at all, do it in
>software.

Well, a bit bold statement, you obviously did
to return the political statement ;-)

But anyways, I will try your negative feedback for high frequencies,
alias 'integrator', for a totally different reason:
The PWM filter, the RC combination that smoothes the PWM to DC, is not perfect.
This causes a slight RF ripple of the drive voltage on the opamp + input,
resulting in a lot of output swing in my circuit.

It is less with higher PWM frequency, but for this PIC microcomputer
a higher PWM frequency means 6 bits resolution, a medium PWM
frequency has 8 bits resolution,
and the lowest PWM frequency has 11 bits resolution, all set by the internal
PIC hardware.
So doing the integrator thing would also filter the PWM better, and quiet things
down some more.
So I will leave in the T filter, as it is proven to work,
but do a test with your circuit added, to see how it reacts to PWM ripple.
If you like <..> I can engrave your name on the alu bottom of the box if it works[1].
I bought a nice engraving tool for about 5 \$ on ebay, and have played with it.
Would that heal any wounds I may have made by being not totally cooperative
in immediately agreeing and sending flowers?

>Tim

[1] Will report back.
```
```I wrote:
[1] Will report back.

+4V
|
R1                                           ---- |
470k              +             R2           |     |
PWM ---===----------------|\          100k     |---      |
0-3V       |     |      - | >---------===----| |<--     === 1u
from      [ ]   ===    ---|/    |              |---|     |
PIC   120k |     | 1u  |       ===        IRLZ34N  |    ///
///    |     |        | C2       on      |
///    | TCL274 | 1u     hotplate  |
|        |        as heater | 0-600 mA
-------------===-----------|
100k          |
R3           [ ] 1.1 Ohm
|  R4
///

So, I changed some components around a bit,
this seems to work OK over the full range of 0 to 600 mA.

I stayed with the standard capacitors of 1uF, and the standard resistors of 100k.
1k is OK for R2, in that the MOSFET does not detectable oscillate,
but then its 880 pF input capacitance is still felt by the opamp.
As we are slowing down things anyway, 100k is better.

What point size of engraving do you prefer?
Please note there is only 80 mm height available.
Of course we can always change to a bigger box.
```
```On Tue, 03 Apr 2012 10:13:55 GMT Jan Panteltje <pNaonStpealmtje@yahoo.com>
wrote in Message id: <jleih8\$ff6\$1@news.albasani.net>:

>On a sunny day (Mon, 2 Apr 2012 06:40:32 -0700 (PDT)) it happened George
>Herold <gherold@teachspin.com> wrote in
>
>?????????????????
>
>
>
>>T24gQXByIDIsIDY6MjOgYW0sIEphbiBQYW50ZWx0amUgPHBOYW9uU3RwZWFsbS4uLkB5YWhvby5j
>>b20+IHdyb3RlOgo+IEkgd3JvdGU6Cj4KPiBbMV0gV2lsbCByZXBvcnQgYmFjay4KPgo+IKAgoCCg
>>IKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgKzRWCj4g
>>oCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCg
>>fAo+IKAgoCCgIKBSMSCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCCgIKAgoCAt
>>LS0tIHwKPiCgIKAgoCA0NzBrIKAgoCCgIKAgoCCgIKArIKAgoCCgIKAgoCCgIFIyIKAgoCCgIKAg
>>oCB8IKAgoCB8Cj4gUFdNIC0tLT09PS0tLS0tLS0tLS0tLS0tLS18XCCgIKAgoCCgIKAxMDBrIKAg
>>oCB8LS0tIKAgoCCgfAo+IDAtM1YgoCCgIKAgfCCgIKAgfCCgIKAgoC0gfCA+LS0tLS0tLS0tPT09
>>LS0tLXwgfDwtLSCgIKAgPT09IDF1Cj4gZnJvbSCgIKAgoFsgXSCgID09PSCgIKAtLS18LyCgIKB8
>>IKAgoCCgIKAgoCCgIKB8LS0tfCCgIKAgfAo+IFBJQyCgIDEyMGsgfCCgIKAgfCAxdSCgfCCgIKAg

[snip]

George posted in Base64 for some reason. Here's what it says:

On Apr 2, 6:23&#2013266080;am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> I wrote:
>
> [1] Will report back.
>
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; +4V
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|
> &#2013266080; &#2013266080; &#2013266080; &#2013266080;R1 &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; ---- |
> &#2013266080; &#2013266080; &#2013266080; 470k &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;+ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; R2 &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; |
> PWM ---===----------------|\ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;100k &#2013266080; &#2013266080; |--- &#2013266080; &#2013266080; &#2013266080;|
> 0-3V &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080;- | >---------===----| |<-- &#2013266080; &#2013266080; === 1u
> from &#2013266080; &#2013266080; &#2013266080;[ ] &#2013266080; === &#2013266080; &#2013266080;---|/ &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|---| &#2013266080; &#2013266080; |
> PIC &#2013266080; 120k | &#2013266080; &#2013266080; | 1u &#2013266080;| &#2013266080; &#2013266080; &#2013266080; === &#2013266080; &#2013266080; &#2013266080; &#2013266080;IRLZ34N &#2013266080;| &#2013266080; &#2013266080;///
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; /// &#2013266080; &#2013266080;| &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080;| C2 &#2013266080; &#2013266080; &#2013266080; on &#2013266080; &#2013266080; &#2013266080;|
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; /// &#2013266080; &#2013266080;| TCL274 | 1u &#2013266080; &#2013266080; hotplate &#2013266080;|
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080;as heater | 0-600 mA
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; -------------===-----------|
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;100k &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;R3 &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; [ ] 1.1 Ohm
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080;R4
> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; ///
>
> So, I changed some components around a bit,
> this seems to work OK over the full range of 0 to 600 mA.
>
> I stayed with the standard capacitors of 1uF, and the standard resistors of 100k.
> 1k is OK for R2, in that the MOSFET does not detectable oscillate,
> but then its 880 pF input capacitance is still felt by the opamp.
> As we are slowing down things anyway, 100k is better.
>
> What point size of engraving do you prefer?
> Please note there is only 80 mm height available.
> Of course we can always change to a bigger box.

Hi Jan,  I like the V-I converter.  It gives a nice linear relation
between voltage in and power out.  Do you stick the 1.1 ohm current
sesnse resistor on the hot plate too?  Why not use a BJT for the pass
element?

George H.
```
```On a sunny day (Mon, 2 Apr 2012 06:40:32 -0700 (PDT)) it happened George
>Herold <gherold@teachspin.com> wrote in
>
?????????????????
>>T24gQXByIDIsIDY6MjOgYW0sIEphbiBQYW50ZWx0amUgPHBOYW9uU3RwZWFsbS4uLkB5YWhvby5j

Never mind, need to add auto base64 codec to my newsreader one of those days..
panteltje10: ~ # base64 -d article.txt

>Hi Jan,  I like the V-I converter.  It gives a nice linear relation
>between voltage in and power out.  Do you stick the 1.1 ohm current
>sesnse resistor on the hot plate too?  Why not use a BJT for the pass
>element?

The 1.1 (actually 2 x 2.2 Ohm in parallel) is soldered directly to the source of the MOSFET
and in that way helps heat the MOSFET, and the MOSFET will heat the hotplate.
I could use a BJT, but that needs driving power.
I could get a darlington I suppose, but I have a bunch of these nice
logic level IRLZ43N (on at about 2 V Vgs), and it is easy to drive from
this CMOS opamp.
I really want to keep the currents in the 4 TCL274 as low as possible,
to avoid any cross-heating in the chip with the light and dark preamps.
So now the output current is zero, this also improves output swing for
this opamp.
I am now working on the power supply with battery backup, so far the most difficult thing!

```
```On a sunny day (Tue, 03 Apr 2012 06:33:58 -0400) it happened JW
<none@dev.null> wrote in <1dkln7lvqd5jtu6f4th3utsodg746l086i@4ax.com>:

>George posted in Base64 for some reason. Here's what it says:ogram

OK, got it, and decoded it with the 'base64' program in Linux.
There is a content header that maybe I should one day have my
```On a sunny day (Tue, 03 Apr 2012 10:46:27 GMT) it happened Jan Panteltje