555 monostable to trigger a 555 astable

Wendy

Joined Mar 24, 2008
22,141
Suggestion: Ever notice the wire kits, the ones with the ends bent 90°? Then look at my drawings of protoboards, my finished circuits really do look like that. I bought a kit box from Walmart to put my wires in, something like the commercial versions. The neater a circuit looks when you finish it the more likely it will work first time. I don't know why, but the rule has worked for me for over 30 years.
 

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thedude123

Joined Aug 29, 2011
39
Suggestion: Ever notice the wire kits, the ones with the ends bent 90°? Then look at my drawings of protoboards, my finished circuits really do look like that. I bought a kit box from Walmart to put my wires in, something like the commercial versions. The neater a circuit looks when you finish it the more likely it will work first time. I don't know why, but the rule has worked for me for over 30 years.
I agree, like when you wash your car, it seems to run better.

I have one of those kits with the wire ends are bent 90deg, yes. I've used them for most of my breadboarding. But for some connections, not all, I used intentional longer "loops" of wires so they could be easilly unplugged and placed somewhere else in the circuit for troubleshooting to get the system to work right. If I were smart enough and knew in advance where each wire were to be connected, the breadboard would look neater, yes. Most likely if I can figure out how to simply have a monostable delayed circuit start the operation of an astable one, or at this point ANY circuit that would delay the operation of a circuit that would blink LEDs then I would go back and "clean up the mess" so I can then install it on a PCB with confidence.
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
Okay, I completely missed the link to the toggle switch - that makes a lot more sense now.

Bill and SgtWookie and other people smarter than myself can comment and correct, but you can add the 4 second startup delay in one of two ways - add another 555 circuit or use an RC circuit.

Now, I haven't played with these much myself just yet, but I've attached a few ideas that may or may not work based on the RC circuit. I don't know if R1 in circuit B or Rb in circuit C is necessary or possibly detrimental, but I added the former to keep pin 4 pulled low (in reset) and the latter to limit current to the transistor.

You'll need to figure out the value for Rt and Ct to get 4 seconds. You can use this to help you: http://www.bowdenshobbycircuits.info/rc.htm.

Note that the 555 operates well below 9V, so you may need to adjust your R & C values to give you a longer time (4 seconds to reach 5V instead of 9V for example, in case 5V is enough to trigger the reset or trigger pins). Alternately, you may elect to add a zener diode so you're sure the output does not go high until the zener voltage is reached. Since you're using 9V, you may have to go with a 8.2V zener such as 1N4738.
I can figure the values for the RESs and CAPs as needed no problem.

The 555 can operate between 4 and 18V as I understand it. And output, or flip/flop values are at 1/3 and 2/3 supply voltage, 3v and 6v respectivly. So I am both confused and interested of your suggestion to use a zener diode...

The pdf of the three circuits is confusing to me as well... The first two are labeled U1 and the third has no label,,, but each pic is labeled Circuit A, B, and C.....?
 
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thedude123

Joined Aug 29, 2011
39
I'm sorry all, but I do not understand why this is so complicated. I have seen way more complicated circuits in this forum. Mine seems simple, Activate a blinking LED after a pause, thats it. I have yet to have anyone explain simply how to activate one 555 circuit from another 555 circuit. Or maybe I'm not going about this with the right ICs..? If not,, any suggestions would be appreciated.

Is it my switching procedure requirement?
Am I not using the right ICs?
Should I be using two astables instead of one mono to trigger one astable?
I'm not married to anything I started with. If it is the wrong starting point then some redirection would be helpfull...

Again, sorry, I do not mean this to sound like a rant and I appreciate everyones help as I understand that they are favors and thank you all. But we are up to 5 pages now and I am no closer to solving this than I was from my original breadboarding....

If there is any further explanation I can give please let me know.

Thank you all very much for your time so far.
 

Wendy

Joined Mar 24, 2008
22,141
Depends on what you call closer. You have a schematic that might work, if it doesn't then state the problem.

You've gotten some good input how to use a SPICE package.

You probably have a better idea how the 555 works.

Unless you declare it, we're not done yet.

If you read back I was wanting to simplify the problem, you can always complicate it again later.
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
Depends on what you call closer. You have a schematic that might work, if it doesn't then state the problem.

Well,, When I use the term "closer" I mean I feel as though I am closer to creating the circuit I need.
Yes, I have provided a schematic,, one that I assume will work, or is a starting point that is open for revisions and suggestions. With all due respect I, nor any novice like me can not create a working schematic of a circuit that I am asking how to build properly. If I could create a working schematic then that would mean that I know how to build the circuit, in which case I would not have started this thread. I have stated the problem and requirments in many posts.

You've gotten some good input how to use a SPICE package.

True,, I have,, and made the changes per the advice. I commented on the results.

You probably have a better idea how the 555 works.

Not anymore then when I first posted actually. I had already done my research and was familiar with the types and how to calculate the times/frequencies, etc. of each. I understand the 1/3 and 2/3 the supply voltage triggering etc,,, I built a spreadsheet to help calculate the values of the Res and Caps given mono or astable, and duty cycle,, etc, etc,,,,,

Unless you declare it, we're not done yet.

What does this mean? I have no solution to my circuit, so I am not done.
I will find a way to make this work. Are you saying I should just declare the thread dead and ask the mods to close it?

If you read back I was wanting to simplify the problem, you can always complicate it again later.

Which post are you referring to regarding simplification? I have tried everything that has been suggested so far and posted the results.
So, am I using the wrong ICs to perform the task I need? Should I go about this in a different way?

Any advice is appreciated,,,
 

Wendy

Joined Mar 24, 2008
22,141
It's not the ICs, it is the weird sequence used to trigger them. I don't really understand what you are trying to do, and this hinders me helping.

I have a full time job and other stuff going on, the last couple of days have been hectic for me. Eventually it will settle down, and I'll be able to focus better. From what I think I understand what you are trying to do it shouldn't be that hard. I'm sure I'm missing something in your requirements, which is why I keep asking for what this circuit is not doing that you need.

So lets simplify the front end and work on the middle. I think this is where you are having problems.

This circuit currently starts off Alarm active, since the monostable starts off and is inverted. This is the bad thing happening.

You want the circuit to start with the Alarm in the off condition. When it is triggered it stays off for a set duration (monostable duration), then triggers on and stays on. This is currently where you are stuck.

The astable basically does what it is supposed to, the beep duration is correct and the dead time between the beeps are correct.

Have I summed up the problem correctly? Understanding is half the battle.

Assuming I have the problem nailed down (and I am not sure I do) you will need an extra part to serve as a memory. This in turn suggests a flip flop (which is memory). I can make a flip flop using gates (like a 4011) or I can use a premade one, something like a 4013.

OK, I'll draw something from these requirements.



The only concern I have with this design is the flip flop formed by U3a and U3b. It is critical that it start up just right, which is why the note about the capacitors exists. During power up C6 predominates, causing the flip flop to power up the way we want.

While I didn't put it in the schematic, you may want a 2nd LED/resistor on U1 output as a diagnostic.

This is the kind of problem that won't simulate well, reality has a way of doing things its own way sometimes.

Side note, a really good website to look up parts and datasheets is http://users.otenet.gr/~athsam/database.htm
 

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elec_mech

Joined Nov 12, 2008
1,500
I thought you stated that when release SW3 (after SW1 is turned on), U1 sends a 4 second pulse to U2 which blinks the LED for 4 seconds. Is this correct? If so, you're farther along than when you started.

Assuming this is the case, now we are on to the next problem: adding a 4 second delay when you release SW3. That is what I was trying to address with my last attachment. I'm sorry, I was in a rush and forgot to label U1 for circuit C. A, B, and C are all ways to add the 4 second delay using the RC method based on some research I've done lately. I haven't had time to verify them, but wanted to offer them to you to try to get you going. The first two use the reset pin of U1 while C uses the trigger pin instead. I've only controlled 555 using the reset pin as I'm not familar with using the trigger pin, but it might work.

If these don't work or you don't want to try them, you can always add another 555 monostable timer for 4 seconds and have it trigger U1 just like you are triggering U2 with U1. You know this will work.

I agree with Bill, the biggest difficulty has been understanding your button start-up sequence. So as it stands, if the user flips toggle SW1 on without first holding down SW3, the circuit will trigger U1 and begin (unless the user flips SW1 off within the initial as yet not added 4 second delay). If the user holds down SW3 then flips SW1 on, U1 will not be triggered on until SW3 is released.

Simplified (and correct me if I'm wrong):
Intended operation:
1) User holds SW3 down
2) User flips SW1 on.
3) Circuit does nothing until user releases SW3.
4) User releases SW3.
5) 4 second delay then LED blinks for 4 seconds then goes off.
6) Another LED blinks for 1 second once every five minutes until SW1 is flipped off.

Alternate operation (if user fails to press SW3 first)
1) User flips SW1 on.
2) 4 second delay then LED blinks for 4 seconds then goes off.
3) Another LED blinks for 1 second once every five minutes until SW1 is flipped off.

You can add another 555 also triggered by U1 (in parallel with U2) with a 5 minute (maybe 1 minute would be better to remind user?) cycle to blink an LED (I think).
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
It's not the ICs, it is the weird sequence used to trigger them. I don't really understand what you are trying to do, and this hinders me helping.

In basic form...

Press and hold a spring loaded switch (S2, (on your schematic)), flip a toggle switch to energize the curcuit,(S1) nothing starts until the spring loaded switch is released, after is is released, delay 4 sec LEDs flash, flip the toggle to turn off the circuit.

Since I have learned how to tie the ics together for "normal" purposes, I can add any extra ICs/features later.



I have a full time job and other stuff going on, the last couple of days have been hectic for me. Eventually it will settle down, and I'll be able to focus better. From what I think I understand what you are trying to do it shouldn't be that hard. I'm sure I'm missing something in your requirements, which is why I keep asking for what this circuit is not doing that you need.

I cetaninly understand the hectic life and appreciate any time anyone can give. I was not getting discouraged due to the time between posts. That would be inconsiderate and narcesistic of me. I couldn't be further from the two. Guess it's been a long week. I apologize if I have offended anyone.


So lets simplify the front end and work on the middle. I think this is where you are having problems.

This circuit currently starts off Alarm active, since the monostable starts off and is inverted. This is the bad thing happening.

Yes and I have been making the mistake of connecting the U1 output to my U2 Pin2. This worked to delay the lighting of the LED but since pin2 was then set to 0v, there was no blinking. This is what made me feel like I was CLOSE...

In my original schematic from back on Post#3 I mentioned that from my research I found that I might need something to invert the output of U1.
Seems like that might just be the ticket. I found this info from this post in another forum.
http://www.electronicspoint.com/triggering-555-another-t224804.html

You want the circuit to start with the Alarm in the off condition. When it is triggered it stays off for a set duration (monostable duration), then triggers on and stays on. This is currently where you are stuck.

YES,,, When connecting U1 pin3 to U2 pin4; Triggering U1, the LED blinks for 4 sec then turns off. This is the opposite of what I need.

The astable basically does what it is supposed to, the beep duration is correct and the dead time between the beeps are correct.

Yes, both U1 and U2 operate as designed by themselves.

Have I summed up the problem correctly? Understanding is half the battle.

Yes. But also, dont forget. I need the circuit to START its operation when the momentary is released. Surely this is easy enough to do...and can simply be corrected later.

Assuming I have the problem nailed down (and I am not sure I do) you will need an extra part to serve as a memory. This in turn suggests a flip flop (which is memory). I can make a flip flop using gates (like a 4011) or I can use a premade one, something like a 4013.

OK, I'll draw something from these requirements.



The only concern I have with this design is the flip flop formed by U3a and U3b. It is critical that it start up just right, which is why the note about the capacitors exists. During power up C6 predominates, causing the flip flop to power up the way we want.

While I didn't put it in the schematic, you may want a 2nd LED/resistor on U1 output as a diagnostic.

This is the kind of problem that won't simulate well, reality has a way of doing things its own way sometimes.

Side note, a really good website to look up parts and datasheets is http://users.otenet.gr/~athsam/database.htm
Bill, thank you again for your help. I have commented within your qoute above. I am new new NAND Gates, or any gate for that matter and have been reading up about them. You mention in your post that one can be made from 4011, or one can be bought, 4013. Radio shack carries niether so I will look ito ordering a few of the 4013 for now, after I understand them better I'll have more confidance to make my own.

In your schematic. Are the gates shown as the purchased 4013 type? Since the 4013 is a quad, Are U3c and U3d in the small diagram to the upper right of the 4013 just not used, but need to be wired to Vcc and ground?

Thanks again....
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
I thought you stated that when release SW3 (after SW1 is turned on), U1 sends a 4 second pulse to U2 which blinks the LED for 4 seconds. Is this correct? If so, you're farther along than when you started.

Assuming this is the case, now we are on to the next problem: adding a 4 second delay when you release SW3. That is what I was trying to address with my last attachment. I'm sorry, I was in a rush and forgot to label U1 for circuit C. A, B, and C are all ways to add the 4 second delay using the RC method based on some research I've done lately. I haven't had time to verify them, but wanted to offer them to you to try to get you going. The first two use the reset pin of U1 while C uses the trigger pin instead. I've only controlled 555 using the reset pin as I'm not familar with using the trigger pin, but it might work.

If these don't work or you don't want to try them, you can always add another 555 monostable timer for 4 seconds and have it trigger U1 just like you are triggering U2 with U1. You know this will work.

I agree with Bill, the biggest difficulty has been understanding your button start-up sequence. So as it stands, if the user flips toggle SW1 on without first holding down SW3, the circuit will trigger U1 and begin (unless the user flips SW1 off within the initial as yet not added 4 second delay). If the user holds down SW3 then flips SW1 on, U1 will not be triggered on until SW3 is released.
BINGO!!

Simplified (and correct me if I'm wrong):
Intended operation:
1) User holds SW3 down
2) User flips SW1 on.
3) Circuit does nothing until user releases SW3.
4) User releases SW3.
5) 4 second delay then LED blinks for 4 seconds then goes off.
6) Another LED blinks for 1 second once every five minutes until SW1 is flipped off.

Alternate operation (if user fails to press SW3 first)
1) User flips SW1 on.
2) 4 second delay then LED blinks for 4 seconds then goes off.
3) Another LED blinks for 1 second once every five minutes until SW1 is flipped off.

You can add another 555 also triggered by U1 (in parallel with U2) with a 5 minute (maybe 1 minute would be better to remind user?) cycle to blink an LED (I think).
You have the procedure(s) correct now, yes.

Yes, maybe 5 min may be too long, but lets get the circuit working properly, I can adjust output times and Hz from component selection easy enough.

It is the delay to trigger U2 to GO that is causing the problem.
It is also the way that U1 requires triggering. The manual pulse to ground from SW3 is not working for me as I need it to trigger only when released.

I do see a third 555 to operate the reminder circuit, yes. This would be a more standard situation and is easy to add once I get the main circuit working properly.

I have replied to Bills post with a few questions as well. We'll see what he has to say.
 
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Wendy

Joined Mar 24, 2008
22,141
If you look closely I mention the 4011 as the quad gates, two of which are waste and must be tied down (this is normal for digital type gates). It saves me making a logic inverter from the 555.

This is a classic set/reset flip flop, a single bit of memory.

A 4013 is two set reset type D flip flops inside one chip (don't worry about the type D bit yet). I would still need an inverted signal from U1 555 output, so I chose not to use it.

As I understand it you want the alarm to be on after the monostable has triggered, but after it has timed out. I'm not sure who has the correct understanding of what you are after, elec mech or I. Only you really know at this point.

Text can be a pain to work with, you are seeing it's disadvantages in this thead. If I understand what is needed I can usually design a circuit from scratch pretty easily, but I have to understand exactly what is needed. I've had this problem with other people too, nuances are easy to miss sometimes.

The sequence as I have laid it out.

1. Hold S2 down.
2. Flip S1 on.
3. Release S2, the circuit starts timing.
4. Upon timeout, the LED and sonalert flash for whatever the time is, goes out, repeats.

I missed one LED, and if you need a flash for one and another flash for the other you will need 2 more 555 timers, in addition to the flip flop circuit, since the flash is a simple astable being turned on/off.

Looking at the time/date stamp, we cross posted, I was writing my reply after you started.
 
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thedude123

Joined Aug 29, 2011
39
If you look closely I mention the 4011 as the quad gates, two of which are waste and must be tied down (this is normal for digital type gates). It saves me making a logic inverter from the 555.

This is a classic set/reset flip flop, a single bit of memory.

A 4013 is two set reset type D flip flops inside one chip (don't worry about the type D bit yet). I would still need an inverted signal from U1 555 output, so I chose not to use it.

Ok,, so your schematic is made using the 4011 gate. Gotcha

As I understand it you want the alarm to be on after the monostable has triggered, but after it has timed out. I'm not sure who has the correct understanding of what you are after, elec mech or I. Only you really know at this point.

I have been commenting on all posts within the qoutes from you'alls posts. Like I am this one. Are you able to read these or should I not do it this way? It is more organized to do it this way as there are many comments and questions within each post.

I gave a basic procedure and result in my last post.
In basic form...

Press and hold a spring loaded switch (S2, (on your schematic)), flip a toggle switch to energize the curcuit,(S1) nothing starts until the spring loaded switch is released, after is is released, delay 4 sec LEDs flash, flip the toggle to turn off the circuit.

Bill,,, yes sometimes hard to explain, but please let me know which part of this procedure is unclear.

Text can be a pain to work with, you are seeing it's disadvantages in this thead. If I understand what is needed I can usually design a circuit from scratch pretty easily, but I have to understand exactly what is needed. I've had this problem with other people too, nuances are easy to miss sometimes.

The sequence as I have laid it out.

1. Hold S2 down. YES
2. Flip S1 on. YES
3. Release S2, the circuit starts timing. YES
4. Upon timeout, the LED and sonalert flash for whatever the time is, goes out, repeats. No Repeat,,, It should go out and stay out.. Adding a third 555 to sound a 1/2sec alarm every 5 min would be great. This is the "Reminder" alarm I mentioned earlier.

I missed one LED, and if you need a flash for one and another flash for the other you will need 2 more 555 timers, in addition to the flip flop circuit, since the flash is a simple astable being turned on/off.

I will add as many 555 timers,, (or 556 to save space), as needed. I have room physically. My final output will be about 6 LEDs and one sonolert.
I did not think that my output would be critical to the circuit operation, but to be forthcoming, that wil be the output. (For my breadboarding, I'm using one LED as output. No sonolarm.)

Looking at the time/date stamp, we cross posted, I was writing my reply after you started.
Thanks Bill,, I hope the above clears some things up..
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
Do you want the sonalert to only go off on the first LED, or both?
Both. It can go off along with the timing of the LEDs, they can work simultainesly.

I was troubleshooting/learning more yesterday about what the timers need to function. I think I'm going to have a problem with the trigger switch on the monostable circuit.
Since the monostable triggering requires a temporary short to ground to start the CAP charge I'm concerned that a momentary switch will not operate properly for this. Any suggestion on a switch or switching "circuit" or component that would provide this temp short to ground when the user releases the switch?
 

Wendy

Joined Mar 24, 2008
22,141
If it isn't too late hold off buying that gate. I've been thinking about it. You need a short power up delay on the alarm group of 555s.

A lot of times these circuits peculate in the back of my brain while I'm doing something else, until a new idea gells. If you ask me to explain how I do it I haven't a clue, but it works. Driving and throne time are the most productive on this.
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
If it isn't too late hold off buying that gate. I've been thinking about it. You need a short power up delay on the alarm group of 555s.

A lot of times these circuits peculate in the back of my brain while I'm doing something else, until a new idea gells. If you ask me to explain how I do it I haven't a clue, but it works. Driving and throne time are the most productive on this.
Bill,
I have not bought them yet. I look forward to reading your ideas.

Thanks again...
 

Wendy

Joined Mar 24, 2008
22,141
A quick explanation why I am going through the contortions of the logic gates or the 555 circuit I am about to draw.

When you look at this circuit...



Note how the capacitor C1 is grounded on the front end. Don't worry about the circuitry the 555 is feeding, I pulled this image from my library. This circuit is a power up reset type, it is a monostable that is triggered by powering up the 555.

When the 555 is low on the output it is ground, there is a switch through a transistor to ground, so you treat the output is ground. If you have a second 555 monostable connected another 555 then you have a configuration that is very similar to that which is shown, and the second 555 will trigger on power up, an undesired operation. This is what I've been thinking of how to defeat. The answer is the reset, if we can delay the power up of the second 555 for about a second or so the input will settle down without triggering the second 555 monostable.

I'll be back on the next post with a couple of possible schematics to fight this.
 

Thread Starter

thedude123

Joined Aug 29, 2011
39
Bill, awesome. this is making more sence regarding the odd way I need the circuit to function. I'm tempted to wire this circuit tonight after a trip to R.S.....
But I think I'd better wait to see what else your thinking....

Thanks again.
 
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