Zener kinda turns on

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

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

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

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

Yep. A 555 is nothing more than a comparator with VCC/3 hysteresis.

Some people here seem to have some problem with precision. It shows in their posts. ...Jim Thompson

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

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

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

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

You can do it quite nicely with a 556 (dual 555)...

Not quite as tight as my first version, but not hack/Larkin level either.

You can also do it easily with an LM339. ...Jim Thompson

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

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

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

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

joke

Tight? Your first hairball had 19 parts to drive two LEDs! Well, this one's only

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

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

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

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

joke

Good grief, you got the functionality wrong!

Remember that time I micowaved a 555 and busted it and then toasted it and got it "working" again? the above circuit was woring with that 555

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

With a 12V supply the zener comes out below 1/3 VCC and the 555 is basically an inverter so a low input converts to a high output lighting the lower LED

What i'm doing is comparing the internal divider with an low precision refernece voltage from the zener

Why? the divider's right. I had the trigger and threshold pins connections wrong though.

If you tie the threshold pin high the trigger pin controls the output and that inconvenient 1/3 VCC hysteresis dissapears.

yeah, but if you do that the hysteresis makes input voltage more critical

Corrected version: +----+---------+------------+-- 5V/12V | | | | | | | V | | | T \\ 5V | | . . . .|. . . . | | | . VCC(8) . 330 | | . . | 1K +---RES(4) OUT(3)------+ | | . 555 . | | +---TH(6) DIS(7)-- 1K | . . | +--------TR(2) CV(5)-- V | . . T \\ 12V 3V3 Z . GND(1) . | zener A . . . .|. . . . | | | | | | | +--------------+------------+-- 0V

I rediced the 10K to 1K to make the zener behave a little better those 3V3 parts are real mushy.

With 3.3V on pin 2 VCC anywhere above 10V registers lights the 12V LED and the lower voltages light the other one

Yeah, that's going to be much more fun it needs another part, they're cheaper parts +-----------+--------------+-----+-- +3-16V | | | | 33K V V | | T\\ 12V T\\5V | | | | | | +-----------------------+ | | | | | | | | +--------100K--+ | | | | | | | | 2K2 680R | | | + | - | | | +--|\ +-------|\ | [LM339] | | >---+ | >----+ | +-----|/ +--|/ | | - | + | +----------------+ | | | 100K | | | +--------------------------------+-- 0V

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

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

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

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

joke

Thompson pretends to killfile me, which is weird since he took my sarcastic suggestion to do this puzzle with 555s.

Would someone please inform him that he botched it?

You need a reference ;-) ...Jim Thompson

unreal! indeed. Both LEDs are off at 4.9 volts, and the "5V" LED is on at 11.9! Plain wrong. I don't know how it behaves as the voltage comes back down, but that could well be snarled too.

Cute. I was trying to find a way to use one of the LEDs as the voltage reference (JT missed that, too) but the damned things are so efficient these days that even tiny currents are visible. I tested one LED in total darkness and was barely able to see light at about 800 pA. 1 uA is plainly visible in room light on a good LED.

Looks like you got hysteresis for free!

Since one LED or the other is always on, the average drop could be useful as a reference.

Are you still fiddling with this lame nothing circuit?

I'm a circuit designer, and this is a cute puzzle.

Why aren't you playing?

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation

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

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

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

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

joke

One LED on at 5V, off at 12V; other LED on at 12V, just as proscribed.

So again we're left with an "ignorati utterance" from Larkin.

As Larkin sig's...

John Larkin Highland Technology Inc

"Precision" BWAHAHAHAHAHAHAHA electronic instrumentation

How can Larkin be so Pecksniffianly ignorant?

Fundamental ancestry of "white/trailer trash" would be my guess. ...Jim Thompson

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

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

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

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

joke

JF

Wrong. Read the OP's requirement. He wants to know if his gear is connected to a 5 volt supply or to a 12 volt one.

Your 555 circuit has both LEDs off at 4.9, and the "5V" LED is on at

Stupid! And look up "proscribed" some time.

Circuit engineer is right, you do seem to be going around in circles on this one :-)

one :-)

Or at least circuitously ignorant >:-} ...Jim Thompson

one :-)

Why do you lurk SED if you're not interested in circuit design?

These little puzzles are fun, and educational too.

Come on, try one yourself. There are lots of possibilities still unexplored.

one :-)

All the circuits that I posted would work. One of yours is a clumsy hairball, and the other one is plain wrong.

I forgot about the TR dominating the THR as a momentary switch while the THR is being held.

Years ago I made an array of 556's on a board as run/jog/stop operator logic switches.

Sink Logic

Vcc | NC .-. E-Stop STOP | | PUll UP NC | | T T '-' --- --- | -o o-+-----+-------+-o o+-----------------------+Threshold | | | | | | T | --- + +--------+-o o+---------------------- Trigger

START/JOG (NO) Hold STOP for jog function. (created by AACircuit v1.28.6 beta 04/19/05

We considered using RS FF but they didn't offer the flexibility of a timer and also, with the timer, we could simply add a time effect to it if we needed a TimeOff/On delay, which we also do that with jumper options and places to put the RC components in for each zone. These were put in custom card slots as modular systems and proved to work very nicely.

I know one of these systems is still operating because I've had to service it for minor details, like dried out caps etc..

So your circuit does agree with me, thanks for the drive down memory lane :)

Jamie

before JF

yet a pen,

Like your crappy drawings? No thanks. One of my main uses for LTspice is schematic capture. Much nicer output, easy to put part values in (especially when you can find semiconductors reasonable close to what you want). Plus if anyone wants to challenge it they have a plenty good file to work from.

Of course i could use my antique Tango Schematic, or my equally antique Circad pretty much as easily.

?-)