Help interfacing Current Transformers to ADC

[Joerg]

The largest loads will be

1) dual 150W magnetic MH ballast, so figure 450W draw during operation
and somewhat more than that due to the inrush when It powers on.
2) All of the pumps are less than 200W motors, and no more than 2 will
be on any given monitored outlet.
3) 500 watt heaters, 1 per monitored outlet.

So most of the stuff will be well less than 10A during operation,
inrush is a different story.

Inrush is usually handled by having a resistor of, say, several kohm
between the rectified and filtered output of your CT circuit and the AD
converter (or the uC if it has built-in ADC). Then a diode to the VCC
rail and another to GND (BAV99 is a nice dual diode for that). The
white-knuckle approach would be to let the internal substrate diodes
take care of things after that resistor, something that's done all the
time. Just don't exceed abs max values.

Now if the CT circuit output voltage spikes when a lamp or motor turns
on the spike is capped.

 

[John Woodgate]

In message <[email protected]>, dated Thu, 14

I forgot. To Brits and Aussies, biscuits are cookies ;-)

To me, a biscuit is what you pour sausage gravy over ;-)

Well, if you snatched one of those away from a Brit, you'd get plenty of
noise. Just ask Genome!

I'm afraid we don't have a proper English word for them; I think we have
to use a - horrors! - French word, 'croute'.

 

[[email protected]]

Now I don't know how
"Southern" squirrels would be

Small, relatinely hairless and tough. Not like those fat tender ones
you get up north.

 

[Michael A. Terrell]

Small, relatinely hairless and tough. Not like those fat tender ones
you get up north.

Often found already cooked at the base of power poles, after they
chew through the protective boots on the primary side of a pole pig.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[beananimal]

Inrush is usually handled by having a resistor of, say, several kohm
between the rectified and filtered output of your CT circuit and the AD
converter (or the uC if it has built-in ADC). Then a diode to the VCC
rail and another to GND (BAV99 is a nice dual diode for that). The
white-knuckle approach would be to let the internal substrate diodes
take care of things after that resistor, something that's done all the
time. Just don't exceed abs max values.

Now if the CT circuit output voltage spikes when a lamp or motor turns
on the spike is capped.

I would MUCH rather stick with through hole stuff. Those tiny SOT
packages are not something I enjoy working with.

So here is where we seem to be at:
Choosing between:

500:1 CT TRIAD CSE187L (cheaper)
-=OR=-
1000:1 AMVECO AC-1020 (better choice)

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

What are the specs I need to be looking for in the bridge?

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

 

[Jim Thompson]

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

I recommend it ;-)

What are the specs I need to be looking for in the bridge?

Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

C1 should be all you need.

...Jim Thompson

 

[Joerg]

Hello Jim,

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

I recommend it ;-)

What are the specs I need to be looking for in the bridge?

Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

C1 should be all you need.

I'd add a resistor between C and the PIC. Low enough to make sure the
ADC in the PIC works fine (I don't know their input circuitry) and high
enough to avoid driving the subtrate diode of the PIC on that input pin
past the abs max limit. Probably a few kohm.

You never know which supply comes up first and driving a PIC via a
substrate diode might not be a good thing. Although I have seen a
schematic where a guy deliberately did that.

 

[Jim Thompson]

Hello Jim,

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

I recommend it ;-)

What are the specs I need to be looking for in the bridge?

Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

C1 should be all you need.

I'd add a resistor between C and the PIC. Low enough to make sure the
ADC in the PIC works fine (I don't know their input circuitry) and high
enough to avoid driving the subtrate diode of the PIC on that input pin
past the abs max limit. Probably a few kohm.

You never know which supply comes up first and driving a PIC via a
substrate diode might not be a good thing. Although I have seen a
schematic where a guy deliberately did that.

Reading comprehension score = 20%, you missed the OP saying...

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

(;-)

...Jim Thompson

 

[Joerg]

Hello Jim,

Hello Jim,

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]


Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf


I recommend it ;-)



What are the specs I need to be looking for in the bridge?


Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.



Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?


Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.



This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).


R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.



Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).


C1 should be all you need.

I'd add a resistor between C and the PIC. Low enough to make sure the
ADC in the PIC works fine (I don't know their input circuitry) and high
enough to avoid driving the subtrate diode of the PIC on that input pin
past the abs max limit. Probably a few kohm.

You never know which supply comes up first and driving a PIC via a
substrate diode might not be a good thing. Although I have seen a
schematic where a guy deliberately did that.

Reading comprehension score = 20%, you missed the OP saying...

Oh, but I think I got at least 25%...

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

(;-)

Sorry, missed that paragraph completely. Thou shalt not do NG on one PC
and filter calcs on the other.

 

[Jim Thompson]

Hello Jim,
[snip]

Reading comprehension score = 20%, you missed the OP saying...

Oh, but I think I got at least 25%...

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

(;-)

Sorry, missed that paragraph completely. Thou shalt not do NG on one PC
and filter calcs on the other.

Are you using a KVM? I'm using an IOGear box with 4-way capability.

...Jim Thompson

 

[John Popelish]

I would MUCH rather stick with through hole stuff. Those tiny SOT
packages are not something I enjoy working with.

So here is where we seem to be at:
Choosing between:

500:1 CT TRIAD CSE187L (cheaper)
-=OR=-
1000:1 AMVECO AC-1020 (better choice)

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

What are the specs I need to be looking for in the bridge?

(snip)

I would probably go for something cheap in a 1 A, 50 V bridge, like
http://59.120.39.77/mccsemi/up_pdf/DB101-DB107(DB-1).pdf
about $.50 each from Digikey. It drops about .7 volts at the current
you will be shoving through it. Of course, you can probably find 1 A
50V axial diodes for about a nickel each. You could also use 4 1N4148
switching diodes that are rated .15 A at 75 for less than that.

If you want to add an extra over voltage clamp to cover an open bridge
diode, you might use a pair of 1N4734A, 5.6V 1W zeners in series
opposing, about $.10 ea.
http://dkc3.digikey.com/PDF/T063/0950.pdf

 

[Joerg]

Hello Jim,

Are you using a KVM? I'm using an IOGear box with 4-way capability.

Only the Barricade router (probably the same that you have) plus another
switch and a printer multiplexer. But when doing filters I use PC#1 (w/
left-hand mouse) for one program and PC#2 (w/ right-hand mouse) for
another or for sims and CAD. Then the window on PC#1 overlaps into the
NG window. I still shouldn't have missed that paragraph.

BTW, in case you ever have to do wave digital filters because there is
no real estate for a full multiplier: TI just came out with a DOS
calculator for the coeffs. Called "wdf_coeff.exe" and comes with the zip
files in app note slaa331. It evens spits out the coefficients in CSD so
it doesn't have to be done by hand. Sweet.

 

[Jim Thompson]

Hello Jim,


Only the Barricade router (probably the same that you have) plus another
switch and a printer multiplexer. But when doing filters I use PC#1 (w/
left-hand mouse) for one program and PC#2 (w/ right-hand mouse) for
another or for sims and CAD. Then the window on PC#1 overlaps into the
NG window. I still shouldn't have missed that paragraph.

BTW, in case you ever have to do wave digital filters because there is
no real estate for a full multiplier: TI just came out with a DOS
calculator for the coeffs. Called "wdf_coeff.exe" and comes with the zip
files in app note slaa331. It evens spits out the coefficients in CSD so
it doesn't have to be done by hand. Sweet.

I'm analog... what's a "wave digital filter" ?

...Jim Thompson

 

[Joerg]

Hello Jim,

I'm analog... what's a "wave digital filter" ?

It's a distant cousin twice removed of the IIR family

These come in really handy if you have to do baseband filtering and the
real estate is tight. Their main advantage besides stability is that you
can butcher their coefficients a little without too much in pass-band
penalties (but you do have to keep an eye on the stop-band). IOW when
trying to get away with the least amount of "ones" in them. Since
subtraction is as easy as addition you can also replace some of them
with "-1" which often further reduces the load. For uC guys the
positions of the "1" or "-1" will determine the number of shift
operations needed to get to each add/subtract while for the chip
designer it's merely a routing matter. Darn, you guys always have a leg
up when it comes to implementing stuff.

 

[beananimal]

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

I recommend it ;-)

What are the specs I need to be looking for in the bridge?

Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

C1 should be all you need.

...Jim Thompson

Sadly, I do not have a scope yet. I would not even know how to utilize
one. That is surely something that is hard to self learn. I keep an
eye out on eBay for cheap units but honestly don't really know what to
look for. I also play around with audio stuff as well. It does however
appear that this is a tool I am going to need to invest in to further
my knowledge and understanding of circuits such as this.

I am going to try and get this simple circuit breadboarded ASAP and see
if how well I can implement it. I just purchased a PIC book today, as
that appears to be the easiest way for me to sample the data and then
async it to the PC as needed.

I feel (and know) I am much closer to understanding this project and
being able to move forward to actually realizing a working prototype.
Thanks!

 

[Jim Thompson]

Hello Jim,



It's a distant cousin twice removed of the IIR family

These come in really handy if you have to do baseband filtering and the
real estate is tight. Their main advantage besides stability is that you
can butcher their coefficients a little without too much in pass-band
penalties (but you do have to keep an eye on the stop-band). IOW when
trying to get away with the least amount of "ones" in them. Since
subtraction is as easy as addition you can also replace some of them
with "-1" which often further reduces the load. For uC guys the
positions of the "1" or "-1" will determine the number of shift
operations needed to get to each add/subtract while for the chip
designer it's merely a routing matter. Darn, you guys always have a leg
up when it comes to implementing stuff.

Do you have some references you can point me to?

...Jim Thompson

 

[John Popelish]

Sadly, I do not have a scope yet. I would not even know how to utilize
one. That is surely something that is hard to self learn. I keep an
eye out on eBay for cheap units but honestly don't really know what to
look for. I also play around with audio stuff as well. It does however
appear that this is a tool I am going to need to invest in to further
my knowledge and understanding of circuits such as this.

I suggest a Tektronix 465 of any variety. For instance:
http://cgi.ebay.com/TEKTRONIX-465-O...yZ104247QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[Homer J Simpson]

Sadly, I do not have a scope yet. I would not even know how to utilize
one. That is surely something that is hard to self learn. I keep an
eye out on eBay for cheap units but honestly don't really know what to
look for.

Almost anything is better than nothing, and scopes have been going for
peanuts on eBay US recently.

A basic scope is 5 MHz. A good one is 20 MHz and a great one is 100 MHz.
Dual channels are nice, and a delay on the sweep is very nice indeed (looks
like a 10 turn pot).

Just make sure it works some - a focusable trace is a good indicator. You
sure don't want to try to find a new tube.

 

[beananimal]

Almost anything is better than nothing, and scopes have been going for
peanuts on eBay US recently.

A basic scope is 5 MHz. A good one is 20 MHz and a great one is 100 MHz.
Dual channels are nice, and a delay on the sweep is very nice indeed (looks
like a 10 turn pot).

Just make sure it works some - a focusable trace is a good indicator. You
sure don't want to try to find a new tube.

I looked several years ago, but was afraid to purcase something that I
was not sure of. I started out looking 5MHz stuff and ended up looking
at 100MHz stuff. I gave up in frustration and lack of the most basic
ability to choose a good used unit. I have shelfs full of impulse eBay
buys that I did not research well.

 

[beananimal]

Hello Jim,

On 14 Sep 2006 13:05:35 -0700, "beananimal" <[email protected]>
wrote:

[snip]

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf


I recommend it ;-)


What are the specs I need to be looking for in the bridge?


Any old bridge will do. You're dealing in only 10's of mA, and PIV of
no more than a few volts.


Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?


Wouldn't hurt... will safely limit any fault currents flowing thru the
ESD diodes of the PIC.


This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).


R1 <= specified value of burden resistor (transformer specs). I'd
avoid going below around 10 ohms, otherwise there may be enough
capacitance seen at the summing node of the OpAMp to cause
instability.

R2 sets Full Scale Range

C1 is chosen to minimize ripple.

I'd test it without the PIC attached and view the output with a scope
to get yourself "calibrated" to how the circuit works.


Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).


C1 should be all you need.

I'd add a resistor between C and the PIC. Low enough to make sure the
ADC in the PIC works fine (I don't know their input circuitry) and high
enough to avoid driving the subtrate diode of the PIC on that input pin
past the abs max limit. Probably a few kohm.

You never know which supply comes up first and driving a PIC via a
substrate diode might not be a good thing. Although I have seen a
schematic where a guy deliberately did that.

Reading comprehension score = 20%, you missed the OP saying...

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

(;-)

Here is what I gather my circuit is suposed to look like:
http://tinyurl.com/f6et7

Here is what I understand that needs to be done (In the event I have
made no errors).

1) I am still unsure of the best choice for the CT (the 500:1 Triad, or
the 1000:1 Avemco)
2) the choice of CT will dictate the size of R1
3) Once R1 is calculated, then R2 needs to be selected to provide the
A/D with a suitable voltage range.
4) The value of R2/R1 gives the Amplification ratio of the inverting
amplifier that is formed by the OP-AMP. In this case it would be 7.87.
So 1mv on the output of the Bridge will provide 7.87mV to the D/A
through R3. 10mV would provide 78.7mV. and 100mV would provide 787mv?
5) The inverting amp is being fed from the negative side of the bridge,
so the output of the amp will be a positive voltage?
6) I think I have the diodes oriented correctly to protect the A/D
input pin from the transients. The more I look at them the more I
doubt myself. I thought I understood what was going on here.
7) From the datasheets I see that the recomended BAV99 package is
faster and has a lower capacitance than the through hole 1n4148s I
chose. I hope this is not an issue for the intended purpose, as I am
not good with SOTs and certainly don't want to do 24 of them at 3 pins
each!

If I am totaly off base, please let me know and I will give this up and
buy more electronics books before I waste anybody elses time.

Lastly: There will be 24 of these in my house running 24/7. After the
numerous open secondary warnings, is there anything else that I need to
do to ensure safety for myself and our home? Honestly, after all of
the grave warnings, I actually feel like (in comparisson) that the act
of poking around the grid voltage and gain stages of my tube amps is
safe!