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The battery symbol in the schematic is upside down.

The short line represents the cathode (negative), and the long line the anode (positive).

Cheers,

If you have the "Insert Image" button above the text entry box, then you are in Full Edit mode. That button is for images on another server somewhere. Don't touch it! Go below the text entry box. See the "Submit" (and 2 others) buttons about in the (side-to-side) center? A little lower on the left a...

Schmidt2LESDs.png Testing "Attachments". Might still be useful. The only change from previous circuit is pot in base's path of Q1. Important - use "Inline" button to put attachment tags in the reply. Cheers, P.S. Thanks T&L/admin, should make some real happy. Works and was easy to figure out how to...

... shall I need a heat sink?

Maybe.

Need input (supply) voltage, regulated output voltage, max current to be drawn, which part number regulator and package. For example, an LM350 in TO-3 may handle more power than TO-220.

What is the "35"? The max and 4.2V the min? With two 9V in series the max available with "near the end" batteries is 12V. 18V fresh. And LM350 needs about 2V difference between supply in and regulated out; so max out is 10V to 16V depending on freshness. With 9V batteries the max "sustainable" (a do...

How much is load current? Output voltage range needed? Is 9V battery the primary supply? What is resistance of poteniometer?

I said 74K. 1M is 13 times bigger! Did you short the wiper to one end to make a variable resistor in series with 10K?

Or ground one end of pot (making a high resistance voltage divider (wrong!).

???
Where did you put it, and how much?

See- https://en.wikipedia.org/wiki/RC_time_constant Going strictly by RC you can increase the time by increasing the capacitor. But , you've got zero ohms in the charge part of the circuit. That can be hard on the switch contacts, and maybe the power supply too. So I suggested increasing the resista...

I've seen this here before. https://drive.google.com/file/d/1xk6dTFshLYfMyfTaCJ56yrI8K77w1EAX/view?usp=sharing Don't make the capacitor bigger. Put a 74K (or nearest standard value potentiometer configured as a variable resistor in series with the 10K resistor. At zero the 10K gives the 2 seconds as...

I'll have to assume a resistor and C1 determines the 2 second time. As 2 seconds will be the minimum time, leave that resistor in the circuit. Add a potentiometer (configured as a variable resistor) in series. The total of existing resistor and variable at max should be (about) 7.5 times the value o...

Below the Quick Reply text box, click the "Full Editor & Preview" button. Then below the larger text boxthat appears, and to the left, select the "Attachments" tab. I don't believe images will attach ... yet. (asof now) to post and image upload to an image hosting site, get the URL from that site, t...

The image button above the text to post box is for URL to image on a server, not the directory and file name on your PC. And it works perfectly. To upload to this site's server you need the Attachments tab below the text box. It is not accepting images (.bmp, .jpg, .png) yet. As they lease server sp...

Congrats to staff! I noticed that sections untouched for years have been removed.

I meant those with an electronic interest will have a tech apptitude and will figure it out. And real beginners can and will get help. The non-tech folks (not even interested) won't be here in the first place. They are not un-invited, they just will not come. And I do not believe making it retart ea...