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.

 

[danadak]

A couple of considerations, again for future designs.

One assumes no action should be taken until 12V supplies fully on. So that
should be detected/handled.

Also when end of 15 sec event occurs, should there be a delay before aux 12
V line is activated, to allow 12V main switch to fully remove its V ?

Lastly the trigger source, is it mechanical switch ? If so should pulse train
be initiated after it goes on then off, or initiated at leading edge of
input ? Reason for asking is if former then switch should be debounced.

The following should accomplish all the above still using ATTINY85 as discussed in
post # 6. Here is what it should look like in block code :

The main loop block group upper left right hand window, and the subroutines called as needed.

The power of programmable devices where appropriate. And simplicity of block programing if
one is new to programing micros.

There is a learning curve associated with above, so stay the course on your 555 approach,
and you can address the above design points other ways if any of them deemed necessary.


Regards, Dana.

 

[danadak]

An example :

I sped timing up to make acquisitions for me easier than twiddling my thumbs waiting
for long delays. Note the 100 mS delay implemented between 15 sec pulse and the 1 sec.
That of course is adjustable. Simple block delay entry. Thats to allow the 12V main supply
to drop to < 1V (just a setting in block code above) before switching on the aux 1 sec supply.

I also looked for glitches on power up, found none. Trigger is bottom trace, implemented as bounce in then
out to initiate pulses. Mechanical generated trigger. Again trivial to change to edge based trigger.

Just a thought....

 

[iAmGrizzly]

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

So I tried what you were saying but still doesn't seem to be right, I have a feeling I'm just not using this program correctly or something though lol again forgive my ignorance with this, I added the ASC file to help figure out where I may have gone wrong.

EDIT: I think I get what your saying the line between C2 and V1 is the issue but how else would power get to those components?

 

[iAmGrizzly]

A couple of considerations, again for future designs.

One assumes no action should be taken until 12V supplies fully on. So that
should be detected/handled.

Also when end of 15 sec event occurs, should there be a delay before aux 12
V line is activated, to allow 12V main switch to fully remove its V ?

Lastly the trigger source, is it mechanical switch ? If so should pulse train
be initiated after it goes on then off, or initiated at leading edge of
input ? Reason for asking is if former then switch should be debounced.

The following should accomplish all the above still using ATTINY85 as discussed in
post # 6. Here is what it should look like in block code :

View attachment 147508

The main loop block group upper left right hand window, and the subroutines called as needed.

The power of programmable devices where appropriate. And simplicity of block programing if
one is new to programing micros.

There is a learning curve associated with above, so stay the course on your 555 approach,
and you can address the above design points other ways if any of them deemed necessary.


Regards, Dana.

Q: "when end of 15 sec event occurs, should there be a delay before aux 12
V line is activated, to allow 12V main switch to fully remove its V ?"

A: No, also it is not entirely necessary to totally disconnect the main 12v line, unless it is not required or interferes with the other parts of the circuit related to the aux 12v line.

(EDIT: I feel I wasn't clear enough here, the main 12v line will run separate from the aux 12v line, the primary purpose of this circuit is to cut off the aux 12v for 15 seconds before restoring is connection, I figured this would also need a delay but that is not entirely necessary for the application)

Q:"Lastly the trigger source, is it mechanical switch ? If so should pulse train
be initiated after it goes on then off, or initiated at leading edge of
input ?"

A: I'm not entirely sure what initiates the power on the aux 12v line, however the amount of time this line is triggered is variable through software settings on the source device. I believe triggering the pulse train off the leading edge of input would be best however adjustments could be made to make it work either way I believe.

I appreciate the insight and help, thank you!

 

[aliarifat794]

You can make a monostable 555 circuit to achieve a 15-second delay and then power a second 555 with a 1-second delay. The first 555 timer will be in monostable mode, triggered when the circuit receives power. The timing is determined by the capacitor (C) and resistor (R) connected to the 555. The delay time for a monostable 555 is given by the equation:

T=1.1×R×C
To achieve a 15-second delay, you can choose appropriate values of R and C.
For example, choosing R = 1.36 MΩ and C = 10 µF gives:
T=1.1×1.36MΩ×10µF≈15 seconds
For the second timer, it will be,
T=1.1×91kΩ×10µF≈1 second

If you want to make a relay switch with the 555, you can see this: https://www.pcbway.com/project/shareproject/555_Adjustable_Timer_Relay_Switch.html

 

[eTech]

You can make a monostable 555 circuit to achieve a 15-second delay and then power a second 555 with a 1-second delay. The first 555 timer will be in monostable mode, triggered when the circuit receives power. The timing is determined by the capacitor (C) and resistor (R) connected to the 555. The delay time for a monostable 555 is given by the equation:

T=1.1×R×C
To achieve a 15-second delay, you can choose appropriate values of R and C.
For example, choosing R = 1.36 MΩ and C = 10 µF gives:
T=1.1×1.36MΩ×10µF≈15 seconds
For the second timer, it will be,
T=1.1×91kΩ×10µF≈1 second

If you want to make a relay switch with the 555, you can see this: https://www.pcbway.com/project/shareproject/555_Adjustable_Timer_Relay_Switch.html

I’ve shown this back in post #13.

 

[ZipZapOuch]

I’ve shown this back in post #13.

No, you didn't. You just jumped to a conclusion that your cascade is the same as what aliarifat794 explained. Read again and then look at your circuit.

The first 555 in your circuit definitely does not power the second because pin #3 of your left 555 is not connected to pin 8 of the 555 on the right, right?

The circuit from aliarifat794 is super easy, makes the auto-trigger on power-up a feature rather than an issue and does not require continuous power to the circuit.

The only issue is his post is the timing formulas. The formulas he used are for a circuit that is continuously powered. The first cycle on power-up is actually slightly different because the timing capacitor charges from zero volts instead of from 1/3Vcc when it is continuously powered.

 

[AnalogKid]

The first cycle

My read of #1:

There are no cycles. My read is that there are two power-on monostables. He is switching power to the 2nd 555 instead of having it continuously powered, and triggering it. Thus, both timers use the standard monostable equation.

ak

 

[AnalogKid]

Forgot to add (and now I can't; what's up with that - ?):

I'm not a fan of using a 555 output as a power source for a downstream circuit. Better to use it as a trigger signal for a normally-powered part. Post #12 is a version of this.

ak

 

[AnalogKid]

Re-reading things, it could be that the fir st 555 is the 15 second delay, and the second 555 is not a timer at all - he is using it as a power transistor to control power to downstream stuff. But if that is the case, then why does the OP mention a 1-second time period?

OR

?

ak

 

[danadak]

OP consider google search "555 timer glitch", a number of hits
on power up. May or may not affect your design.

What accuracy do you want in your timing. Many electrolytics come
with a room temp +/- 20% accuracy initially, and add some T
change to that, 5-10%, and DC bias effects, not exactly a precision
approach. Add to that lifetime effects on C and timer
threshold accuracy and V effects. Not pretty, but for some aps
OK.

I am trying to find a spice model for a electrolytic with T and V effects
to sim to see if I can get to overall predicted accuracy.


Regards, Dana.

 

[iAmGrizzly]

Re-reading things, it could be that the fir st 555 is the 15 second delay, and the second 555 is not a timer at all - he is using it as a power transistor to control power to downstream stuff. But if that is the case, then why does the OP mention a 1-second time period?

OR

?

ak

The timing of the second part is technically arbitrary, you're correct that I'm essentially trying to use the 2nd 555 as a transistor. I have considered just trying to find a transistor that fits the bill and going with that, I feel like that would simplify things quite a bit. Also if you have the time could you put together the circuit from post #12 in LTspice? I've been trying to figure it out myself but I can't seem to grasp this program. Might just try to put it together on a breadboard and try it that way...

 

[iAmGrizzly]

So I finally had some success with LTspice, I found out the issue I was having simulating the circuit was from a missing variable. With this the first part of the circuit functions properly in the simulation, posting this so hopefully it will be helpful for other people learning the program. This is the source where I found the mistake I was making https://www.eevblog.com/forum/beginners/simple-555-timer-delay-on-not-working-on-ltspice/

Added the ASC file that I had work for me, delay on this one is around 18s but can be adjusted by changing the value of R2 & C2.

I'd like to thank everyone again for their help, I think we are getting close to a solution

 

[iAmGrizzly]

Hey everyone I finally had success in LTspice getting this circuit to work! adding the file along with this post. If anyone has any insights to improve this design I am more than welcome to input. I will try to assemble the circuit and test in the real world soon to see if it performs similar to the simulation and then I will make this the solution. Until then I'd like to thank everyone again for their contributions, this forum has been very helpful for me and I feel I've learned a lot in the past few days