555 Delay On Circuit

[iAmGrizzly]

Hey guy's, I may find the solution before someone answers here but I figured if it can save me sometime might as well double down.

Trying to figure out how to setup a monostable 555 circuit to add a 15 second delay upon receiving power, then power a second 555 with a shorter 1 second delay. I found a few different circuits just searching the web but whenever I try to simulate them in LTspice I'm not getting the type of readings I was expecting. Essentially the goal of what I am doing is to get the first half of the circuit to wait 15 seconds then power a second half that has a shorter delay (1 second) that will receive its voltage from a secondary source.

I know it would probably be better to use relays but I have loads of 555 chips on hand already so if I can figure something out just using these then that would be nice. Any help would be greatly appreciated.

 

[Lightium]

The first "then" indicates a 2nd delay.

 

[danadak]

555 timer - Search - Anna’s Archive

annas-archive.org

 

[ChrisP58]

Please post your LTspice file to make it easier for others here to help you. I would also ask for a timing diagram of what you want the circuit to do.

 

[crutschow]

It's not clear what you want.
What does the second 1s delay do if you already have a 15s delay in front of that?
Or do you mean a 1s pulse after a 15s delay?

 

[danadak]

A quick and simple way (future designs) :

Use ATTINY85. mBlock takes your block config and converts that into Arduino code you
then program the ATTINY85. So when this powers up output 0 goes high. Then 15 secs
later output 1 goes high. Is that what you wanted ?

Timing accuracy over T and V is +/- 10%, with user cal +/- 1%, or use $ 3 board
~ .1%.

A sophisticated timer with various triggers :

Pulse Sequence Generator / Smart Timer

Often users, developers, hobbyists need timed and qualified event generators, many resorting to 555 timers and the like. The venerable 555 has had a long run but its limited in accuracy and capability. This approach uses block language to create...

www.electro-tech-online.com

Regards, Dana.

 

[ZipZapOuch]

Hey guy's, I may find the solution before someone answers here but I figured if it can save me sometime might as well double down.

Trying to figure out how to setup a monostable 555 circuit to add a 15 second delay upon receiving power, then power a second 555 with a shorter 1 second delay. I found a few different circuits just searching the web but whenever I try to simulate them in LTspice I'm not getting the type of readings I was expecting. Essentially the goal of what I am doing is to get the first half of the circuit to wait 15 seconds then power a second half that has a shorter delay (1 second) that will receive its voltage from a secondary source.

I know it would probably be better to use relays but I have loads of 555 chips on hand already so if I can figure something out just using these then that would be nice. Any help would be greatly appreciated.

Your problem is likely cause by the first cycle of the 555's timing capacitor charge from 0 to 2/3Vdd. Subsequent cycles go from 1/3v to 2/3v. So, plan your timing accordingly if you are charging from the first connection and the timing cap is completely discharged. If you trigger twice in short succession, you may need to discharge the capacitor completely as part of the trigger to keep timing consistent.

 

[AnalogKid]

Better to have both 555's powered continuously, and have the first 555 *trigger* the second one. This works by having the first 555's Output connected to the second one's Trigger input through an R-C differentiation network.

Are your parts bipolar of CMOS?

ak

 

[danadak]

Interesting comments by ZZO, no such problem in the micro.

But micros not totally immune to issues. There is a "no mans land" of
output uncertainty when powering up, so choose micro wisely. Better
datasheets show a region of Vdd operating for valid output.


Regards, Dana.

 

[ZipZapOuch]

Interesting comments by ZZO, no such problem in the micro.

But micros not totally immune to issues. There is a "no mans land" of
output uncertainty when powering up, so choose micro wisely. Better
datasheets show a region of Vdd operating for valid output.


Regards, Dana.

Unfortunately, the OP asked for solutions to use his stock of 555s.

 

[danadak]

And thats why I said

A quick and simple way (future designs) :

With the follow on post showing additional advantages in using the "future" possible micro....

 

[AnalogKid]

First pass at the requested dual-555 circuit.

R1-C1 is the 15 second power-on delay. R2-C2 is a differentiator to compensate for the 555's non-monostable behavior. It turns the U1 output trailing edge into a short trigger pulse. Its period is not critical, but must be less than the output pulse width. R3-C3 sets the 1 second output pulse time.

For both timers, the pulse width is 1.05 x R x C.

R4 provides a discharge path for C1 and C3 when power is removed. C4 and C5 are power supply decoupling caps for the two ICs.

The two ICs can have different power sources, but the two circuits must share a common GND.

Click on the schematic for a larger image.

ak

 

[eTech]

This uses NE555 chips. The LED's are optional.

 

[iAmGrizzly]

Hey guys sorry for the delayed feedback! I really appreciate all the help here, I'm going to comb through all this tonight and let you guys know what works best for me.

Please post your LTspice file to make it easier for others here to help you. I would also ask for a timing diagram of what you want the circuit to do.

Unfortunately I didn't save any of them since I couldn't get the results I wanted and it was a fairly simple circuit to put together. It looks like several of the schematics here are close to what I was trying.

It's not clear what you want.
What does the second 1s delay do if you already have a 15s delay in front of that?
Or do you mean a 1s pulse after a 15s delay?

Just to clarify a bit more here is the situation. There are 2 seperate 12v lines, one is always on, and one is momentarily on. The issue is when the device is powered on by the main (The always on line will be "main") it sends a constant 12v down the momentary line as well which causes a conflict shortly after.

So what I am trying to achieve is basically having the first 555 start when the device is powered from the main, I want to run the momentary 12v line through a 2nd 555 that is off, this way no current will be allowed through until AFTER the first delay. Then once all of that is complete the 2nd 555 will stay on but with short delay so the momentary 12v line can do its thing.

The main device is a amusement machine so what happens when the momentary 12v line is energized for longer than 5 seconds or so, it makes the machine go into an error because it sees that as a coin slot being stuck closed.



Again thanks everyone for your contributions! I will try some of these solutions tonight and let you know what works best for me as soon as I'm able to

 

[danadak]

Do 555 timers have well behaved power up behavior ? No output
glitching ? Especially if supply has slow risetime ?


Regards, Dana.

 

[iAmGrizzly]

Better to have both 555's powered continuously, and have the first 555 *trigger* the second one. This works by having the first 555's Output connected to the second one's Trigger input through an R-C differentiation network.

Are your parts bipolar of CMOS?

ak

One will be powered continuously however I would like the second one to remain off for the short duration that way no voltage will pass through it before the first delay. Bipolar

 

[iAmGrizzly]

Do 555 timers have well behaved power up behavior ? No output
glitching ? Especially if supply has slow risetime ?


Regards, Dana.

They're well behaved for the most part, to my knowledge they don't work well if you need super specific timing of things but if the values don't need to be spot on then usually they're fine.

EDIT: side note the supply gets to 12v immediately so that shouldn't be an issue

 

[danadak]

If you have a scope easy test to check out using scope on single shot
trigger to capture power up sequence. Say trigger off supply pin,
~ 100 - 200 mV, and look at outputs, see what they are doing.

No supply has immediate rise time.

Note it may not be a problem for your application if short glitches
occur that downstream circuits do not respond to, thats up to you
to confirm.


Regards, Dana.

 

[iAmGrizzly]

First pass at the requested dual-555 circuit.

R1-C1 is the 15 second power-on delay. R2-C2 is a differentiator to compensate for the 555's non-monostable behavior. It turns the U1 output trailing edge into a short trigger pulse. Its period is not critical, but must be less than the output pulse width. R3-C3 sets the 1 second output pulse time.

For both timers, the pulse width is 1.05 x R x C.

R4 provides a discharge path for C1 and C3 when power is removed. C4 and C5 are power supply decoupling caps for the two ICs.

The two ICs can have different power sources, but the two circuits must share a common GND.

Click on the schematic for a larger image.

ak

View attachment 147501

So I attempted to copy the first part replacing the output with a LED just for testing sake, I feel like I have something setup wrong though. Getting 850mv through output. Fairly certain I just have this setup wrong, I'm new to using this kind of software so forgive my ignorance lol

EDIT: I noticed I did miss a connection but even after connecting that other resistor it didn't fix it

 

[AnalogKid]

You have the Trig and Thrs inputs connected directly to Vcc, and the bottom end of R2 is floating. Break the connection to Vcc, and connect R2 to Trig and Thrs.

ak