Time Delay Without A 555 Timer ?


When it comes to electronic circuits I'm a mix between a newb and a novice. What I want to do here is make a circuit closed for 3 seconds (doesn't have to be exact) then open till the circuit is reset. Is there a possible way to do this without using a 555 timer?

Thanks in advance.

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iceng5 years ago
Here is one of two circuits I designed just for you.  .  .  A
timer scr.GIF
If you Mention the value of the C and R1 it will be helpful.......
This is not a 555, this is a straight RC time constant situation but that depends on your DC supply voltage ?

And if it is less then 50VDC you will need to replace the 35V diac with a
10 volt motorola type diac.

I like to start with a 0.1uF capacitor and find a value of R such that the
66% of voltage occurs in RC seconds.

There will be some experimentation needed because the diacs
break-over voltages vary by +-10 percent...

Re-design5 years ago
Nope, it can't be done.  Timers didn't exist until the 555 was invented.

Well, that's a lie.

There have been timers almost from the beginning of electronics.  Even before tubes.  Then they used tubes then transistors.  Now ICs are made so that almost everything is in one package.

Check out this instructable.  Especially the Radio Shack diagram for 1972.  It contains EVERYTHING you need to do your project.  But you have to figure out what's going on and adapt what's there to what you need.  It's very close but not exactly. 

Check out the links in the posts.  The link to the transistor tutorial page is really full of great info.

Good luck.

Here's another good example.

Google "Resistance capacitance timer schematic" or "rc timer schematic" for more examples.
Seifpic (author)  Re-design5 years ago
I like the Resistance capacitance idea but can it be used so that it outputs high for 3 seconds then low till the circuit is reset? If so can you show me how since I don't really understand how I'm going to use it for my purpose (turn on an electromagnet for 3 seconds then off until the circuit is reset).

Thanks In Advance.
Of course it can. Use a transistor flip-flop on the output.

Or a normally open relay.
seandogue5 years ago
Look up the 74121 "one-shot". That would be the original standard logic part number, but there are also newer variants. Quite a useful IC.