Regulating Voltage with LM78XX

X-Face: ?)Aw4rXwN5u0~$nqKj`xPz>xHCwgi^q+^?Ri*+R(&uv2=E1Q0Zk(>h!~o2ID@6{uf8s;a+M[5[U[QT7xFN%^gR"=tuJw%TXXR'Fp~W;(T"1(739R%m0Yyyv*gkGoPA.$b,D.w:z+ idea how to determine them. The circuit just said 12V for the relay and

true, if you have a 12V relay, measure its resistance, halve that and put a resistor approximately that size in series with the relay (+/-10% is close enough). you can treat the combination as an 18V relay

as long as whatever that's going to be sqitching the relay on and off can handle 18V instead of 12V you'll have no problems.

Bye. Jasen

I am the OP and the circuit is from:

I wanted the circuit to shut off a 120V outlet after 2 hours. (I'll google a time delay relay), sometimes you just don't know the key word to query?

I do not know much but how to follow a simple schematic is sometimes taxing to me, as are most things to do with math. I was assaulted three years ago and suffered at least one concussion, and three skull fractures which has left me with about 20% of what I had for brain power and remembering s*it. I'm not complaining, just living with it and doing the best I can.

Thanks for all the responses. I had not seen many options for any timer over 60 seconds much less the 2hrs that I need. Funny thing is that I was a programmer for 36 years, and I can still do that, although it's very slow. Analogy is I used to be a brick layer that could do 1000 bricks a day, now I can struggle and do 200. I can still do it but much too slow to work it as a profession any longer.

Thanks again for all the help; Don

Hi, Don. Your link to the 4060-based timer circuit explains a lot. Yes, you do need a steady DC supply if you're going to use this circuit (which is similar to the standard Time Delay Relay module of the 1970s and early '80s). Your circuit will cost a lot less than a TDR, especially if you've got the 12V coil relay in your junkbox, and it should work well. You also need a voltage within +/-20% of the nominal relay coil voltage when the relay is on. So it might be best to just go with a regulated output +12V supply, like another post suggested.

Good luck with your project. I shouldn't have cast aspersions -- how should a newbie be expected to know the right way to phrase a question unless he already pretty much knows the answer? This ain't Plato's Cave, it's just a newsgroup. :-P

Cheers Chris

(snip)

Thanks for the link. Now we know what you are talking about.

The cmos counter chip (CD4060, with 16 pins)

What DC voltage source do you have available to drive this circuit (between the +VE and -VE terminals on the schematic)?

Ideally, you should pick a small relay that matches that supply voltage.

Here is an example of a digital time delay relay that has something like this circuit inside it:

Chris; (I looked at the link for the time delay relays, they did look a bit out of my budget). No aspersions were ever taken or considered, but I did fail to mention the circuit, (not intended but, pretty vague on my part). I usually over do it on information since in my old job (as here) it was so very important to be precise and not be led down the river of no return, "He who fails to plan, plans to fail". I dug up my last 7812 and I have a full wave bridge, now its up to me to get everything in the right direction and place. You all have been very helpful, and I appreciate all the time and effort/knowledge that is required to respond to my posts. Too often, someone gets help and does not even have the decency to say a simple thank you, I hope I said it well enough! Thanks to all and I certainly appreciate all the help; Don

Thanks for the link, I was going to get a 12-18V transformer and the relay is 12v and I have my last 7812 available and all the other parts.

John; Thanks for the insight and link! (hindsight foresight comes into play here since I can get the whole package for under $50). Thanks again, I have bookmarked the page for my next easier project, all in one! Thanks again; Don

John P>

true, if you have a 12V relay, measure its resistance, halve that and put a resistor approximately that size in series with the relay (+/-10% is close enough). you can treat the combination as an 18V relay

as long as whatever that's going to be sqitching the relay on and off can handle 18V instead of 12V you'll have no problems.

Bye. Jasen