Zener kinda turns on

For me, using LTSpice, that switches at about 14 volts.

Use a .dc sweep analysis. you'll see what I mean.

be

and

Just open your links with left doohickey and close with right doohickey () and they'll function properly.

Who's passing all the farts, otherwise known as excess line feeds ?:-} ...Jim Thompson

You gets what you pays for >:-}

Went to an MIT wine tasting last night at il Vinaio (270 W Main St Mesa, AZ, Great Place!). I have to adopt and modify a Henny Youngman phrase scrolled on the wall: "I just turned 73, but I still don't need glasses. I just drink straight from the bottle" ;-) ...Jim Thompson

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

"I _think_ I can remedy this problem by changing R2 to a lower value..."

Why not "do the math" instead? Seat of the pants guessing is NOT engineering. ...Jim Thompson

will be

and

lights.

current:

No. At 5V ish (gate source threshold, the 5V LED is on. At 12V ish and beyond, both LEDs are on

Regards

Klaus

Well, I did. This circuit is not intended for precision and neither are the values picked thoroughly for the precise voltage levels, just depiction of the general idea.

Regards

Klaus

ator turns on and if you power it up with 12V the 5V LED goes off and the 1

OFF until I provide it a voltage drop of 5.6V, and since it's in series wit h some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 L ED light up... I'm basically measuring a little over 1V at the gate.

ke 1k maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

pdf

This is going to vary much with temperature and production spread of the VB E of the BZX70 transistor for the 12V level. The same for

Cheers

Klaus

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

the BZX70 transistor for the 12V level. The same for

Yep. But Larkin thunked it up, so it must be wonderful, just like his "invention"...

Where I come from we call that "an utterance of the ignorati" ...Jim Thompson

will be

and

lights.

current:

both LEDs are on

I was referring to your first schematic; I didn't realize that there was a second sheet in the thing that you posted.

The max gate threshold voltage of a 2N7002 is 2.5 volts. That probably happens at Vcc=5, but it's borderline at, say, 4.5 volts and some temperature swing. It's a battle of picoamps between the LED, D1, and Q1.

If you rearrange it slightly, and remove some parts, it starts to look like this:

or

which has some both-led-on overlap at intermediate voltages.

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

the BZX70 transistor for the 12V level. The same for

The base drive voltage is 0.36 at +5 and 0.86 at +12. It will work with any BCX70 at any temperature that people can stand. As I said, add a bandgap in the "13K" leg if you don't trust silicon.

indicator turns on and if you power it up with 12V the 5V LED goes off and the

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

of the BZX70 transistor for the 12V level. The same for

It will work, with about a fifth as many parts as the insane brute-force joke you posted.

Try again, something realistic this time. Use a 555 or something, before JF beats you to it.

I call it blank verse. Klaus did most of it, although it's not really is fault. Please blame the new, improved, and poorly designed Google Groups, with it's bad habit of double spacing quoted text.

His initial posting quoted your 52 line posting turning it into a 91 line posting. He then added a few lines twice to his own posting resulting in 183 and 363 lines respectively. A reply to comments by John bloated it to the current record of 796 lines. If he reappears, is certain to double again, and again, and again...

Google shows no interest in fixing the problem which it created, so it is up to the Google users to edit or just eliminate quoted text. Better yet, to abandon Google Groups and use a real Usenet news reader.

Amen! ...Jim Thompson

indicator turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

would be OFF until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

value... like 1k maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

pdf

the VBE of the BZX70 transistor for the 12V level. The same for

joke

JF

Cool beans idea. I already see how to do it with a 7555. If i can get LTSpice to cooperate enough i will even post it.

?-)

here's one way.

on rethinking that circuit doesn't make any sense, I think I must have been was using a damaged 555 when I got that to work,

maybe with a zener twice the size,

I am afraid that isn't going to work that way, for a couple of reasons.

1. You have the output orientations backwards. The Threshold point will turn off the output, which will then activate the upper LED. Simply change the labeling for those two to fix that.
2. Internally you have a voltage divider of 1/3 and 2/3 of the Vcc, since you are raising the Vcc, it'll never reach the threshold. To fixed that, you need to supply the Vcc with a fixed 5 volt or less supply. Also, you most likely can tie both the trigger and threshold together.

When it's all put together with the proper voltage divider, that will work nicely.. Don't forget that you can use the Discharge output to drive an LED. You don't need that zener unless you want to protect the inputs from over 5 volts and the Vcc rail could be supplied via a basic 78L05 reg..

Jamie