I like the idea of two LED's to indicate presence of AC. I'm trying to figure out how to modify the circuit Alec posted (which is appreciated). So far I'm not confident my drawing will work. At this point I'm open to any other ideas, as well as the notion of my original idea of using a current mirror circuit.

Years ago; a small blue square PTC component became the standard start up resistor in TDA4600 SMPSUs - it crossed my mind that it might work in a similar manner to the PTC device in the voltage/continuity tester I mentioned, but I can't remember if I ever got around to trying it.

 

I would have thought a PTC would need to pass considerable current so as to heat up and change its resistance dramatically to be useful as an "auto-ranging" device for the tester. It's not usually desirable for test instruments to gobble a lot of current from the DUT.

 

I would have thought a PTC would need to pass considerable current so as to heat up and change its resistance dramatically to be useful as an "auto-ranging" device for the tester. It's not usually desirable for test instruments to gobble a lot of current from the DUT.

The one in the commercial tester was a thin film on a ceramic tube former and had very low thermal inertia - the LEDs were ultra efficient 2mA types.

The TDA4600 startup PTC probably has a lot more thermal inertia - I can't remember if I got around to trying one.

There are probably lowest end Polyfuse devices that will do - but probably not with ultra efficient LEDs.

 

Can I get a little help with LTSpice? Finally figured out a very little about what I'm doing. So when I try to run this SIM it reports "No Analysis Command Found". I tried the net name thing AND the "OP." command but I have never used this before. Here's my circuit in LTSpice:

 

Delete the two '.op' commands from the schematic. A transient analysis (.tran) then works ok. If you actually want to do a DC operating point analysis (.op), then click 'Simulate/Edit simulation command' to bring up the pop-up for changing mode. For the .op mode you will find it handy to have net nodes labelled with something meaningful, e.g. 'cap', 'in', 'out'.
You have a label 'Voltage_detector' that is floating. Perhaps you meant that as descriptive text instead? Note: the 'Label' tool and the 'Text' tool are for use with circuit nodes and descriptive text respectively.
BTW, the 'amplitude' parameter of a sine voltage source is the peak voltage, not the rms voltage. So perhaps for V2 your '120' should be '170'?

 

@Alec_t: Thank you. The videos I've seen on YouTube have been barely helpful, and I understand that LTS is not your run-of-the-mill circuit simulator. It will take some serious learning to get proficient with it.

Is there a tutorial or some other site that will list all the commands and instructions on how to use them that you know of?

I'd like everyone to know I appreciate the help. Even when I'm wrong. I'm not above learning something new. Even as an old dog - I can still learn something new. Thanks again. And thanks to all.

 

Oh how wonderful! Now I get the message "Missing stop time for transient analysis".

Heads up - I'm using MAC and I don't have the handy tool bar across the top. Is there a work-around or do I have to continue to search for tools via Right Clicking?

 

Hello,

There are many tutorial PDF's on the net:
LTspice tutorial

I also posted a quickchart in this thread:
LT spice models

Bertus

 

I don't know how LTS works on a Mac, but there must be some way of setting the stop time for a .tran analysis. Don't you get an 'Edit simulation command' pop-up?
The LTS 'Help' (which you presumably have access to on a Mac) is actually helpful and explains most things you need to know, albeit somewhat cryptically on occasions .

 

E-mailed LTS. They said they removed the tool bar from the Mac OS X because it was counter productive to use it. WHAT?! I thought it would make my task easier. No, they said it was originally designed with the intention to use "Right Click" to access the menus. Go figure.

Here's a cut and paste of the actual return message:

I removed the toolbar from the Mac OS X version because it usually counter productive to use it. The software was always intended to be used with right mouse click menus and hot keys.

--Mike

Whatever. I'm still trying to figure out how to apply a "Stop" command. True, I've been out running Mother-in-law around for six hours. So I'll stab at it again. maybe I'll hit something vital. The SIM! Not the MIL.

 

Hello,

Did you see my thread?
There is this image with shortcuts:

Bertus

 

I'm still trying to figure out how to apply a "Stop" command.

Can you post a screenshot of your Mac display when running LTS, showing in particular any tabs/controls etc?

 

Hi,

To run an LED from sources from say 12v to 120v you can use a constant current regulator. The constant current regulator keeps the current at the level required for an LED. If you use a high brightness LED you can get away with as little as 5ma. Constant current regulators using a single transistor are not hard to design.

 

Alec:

Here's those screen shots you requested: #2, 3 & 4 are with the drop-down menu's from "File" "Edit" & "Window". Only "File" had any additional drop-down menu's but I didn't bother to shoot them because - obviously they would't hold any secrets.

I'm going to be moving Mother-in-law this weekend, so I'll be away from the computer until next week. I may find time to sneak in and post something, but generally I won't be available.

 

What do the icons at top left do? Are the three circles in the top row significant?

I presume the bottom left icon represents 'run', but does that give you options for setting the stop time or other sim parameters?
Good luck with the MIL move.

 

The little "Running" man "RUN(s)" the sim. Haven't figured out the hand yet, the hammer opens "Waveforms", "Save Defaults", "SPICE", "Drafting", "Operation" & "Hacks". In each of those tabs there are no settings that I can see where I can define a "Stop Time".

Meanwhile I think I've come up with a way to build this probe. The attache drawing shows two LEDs. One GREEN and one RED. When probing a positive voltage the green LED will illuminate. When probing a negative voltage (actually a reverse current) the red LED will illuminate. If both LEDs illuminate then I know I have AC. Q3 is current limited and inverted to run the current from Probe 2 (ground) to Probe 1.

ANYBODY: Do you see problems? Is 10 mA enough to illuminate the super bright LEDs? I suspect they are approximately 2Vf & 3Vf (red / green). There's an idea, a Red/Green LED. One color or the other and I have a direct current (forward or reverse). If yellow - AC. What'cha all think?

 

Haven't figured out the hand yet

Perhaps that does the 'Stop'?

Do you see problems?

The current mirror doesn't work for Q3. Negative voltage on Probe 1 will result in Q3 passing very high current and getting fried.
Anything above 40V will exceed the absolute maximum voltage rating of the 2N3904.