# 555 monostable with multiple inputs and outputs

#### HW-nut

Joined May 12, 2016
94
The circuit is getting complex enough where a small micro-controller would be simpler (i.e. Arduino).

#### ScottWang

Joined Aug 23, 2012
6,926
Thanks a lot ScottWang, thank you very much for your time truly appreciate,

As mentioned I’m totally new to electronics, so starting with small steps, I would have clearly used three 555s for three different buttons and outputs, but I just wanted to know instead of using 3 identical circuits can’t we use single circuit with the help of pushed input to derive the output. This solution might be expensive than having 3 separate 555 monostable circuits, but this solution definitely taught me lot of things.

Thanks again and I can’t believe how helpful and nice all of you in this forum
@Alect_t - as I mentioned I may not need to keep it 30 seconds on, probably less but the idea is for me to learn something I couldn't figure out myself
If I just tell you that using three 555 are more easier then maybe you can't imagine that, even using two CD4093 could do, but for a new learner, the things more simple are more easy, for a uC user maybe will give you the uC is more easier, that is the different position different thought, how to get to the top of the mountain, just point out the way and let you go alone or show you the way on map, or bring you to climb the mountain, which way is the best way to you, it is all depends on you.

#### crutschow

Joined Mar 14, 2008
25,269
The circuit is getting complex enough where a small micro-controller would be simpler (i.e. Arduino).
I wouldn't recommend that to some who describes himself as "totally new to electronics".

#### vinras

Joined May 11, 2016
6
If I just tell you that using three 555 are more easier then maybe you can't imagine that, even using two CD4093 could do, but for a new learner, the things more simple are more easy, for a uC user maybe will give you the uC is more easier, that is the different position different thought, how to get to the top of the mountain, just point out the way and let you go alone or show you the way on map, or bring you to climb the mountain, which way is the best way to you, it is all depends on you.
Agree, nowadays we could do these type of thing using Arduino, but for me it doesn't feel right, it is not pure electronics, it is programming on top of on something someone built, it will not teach you electronics much but it will teach you how to use existing device with some programming. I had uncle who was excellent at building circuits he didnt have any higher education but he could build anything, unfortunately he has passed away and i couldnt spend enough time with him to learn it from him.
using three 555 timers may not lead me to thinking how to use latches or flip-flops, now I know something called latches are there to keep store the state, so I can learn about it and use in different project other than this

I'm going to order few components (74HC74) and try out this circuit to understand it, even though my practical solution to original question end up with using three 555 option.

Can I ask one question regarding your design, so the actual driver to make the given LED on is the push button signal? and the pin 3 output is the one make it off after given time out period?

#### ScottWang

Joined Aug 23, 2012
6,926
Agree, nowadays we could do these type of thing using Arduino, but for me it doesn't feel right, it is not pure electronics, it is programming on top of on something someone built, it will not teach you electronics much but it will teach you how to use existing device with some programming. I had uncle who was excellent at building circuits he didnt have any higher education but he could build anything, unfortunately he has passed away and i couldnt spend enough time with him to learn it from him.
Yes, if you want to learn EE then learn it from the basic bjt, R and C, using arduino is for application, it can't give you the basic conception, or any uC are the same.

Interested in something could cause learning motive and focus on it, your uncle just like that, and he enjoy that and became a circuit design expert, no matter what does his education, focus generate power.

using three 555 timers may not lead me to thinking how to use latches or flip-flops, now I know something called latches are there to keep store the state, so I can learn about it and use in different project other than this
555 can do many different functions, it could be hundred and hundred, so it can be the latches or flip-flops in their(ne555 and cmos 555 as TLC555) ways, you just google it then you will get much more functions you want.

I'm going to order few components (74HC74) and try out this circuit to understand it, even though my practical solution to original question end up with using three 555 option.
Long time ago, I was used 74LS74 and then I changed to cmos type CD4013, so I didn't prepare the 74CHC74, in your case the logical needs a low level to trigger it, so I chose 74HC74, otherwise I will use CD4013.

Can I ask one question regarding your design, so the actual driver to make the given LED on is the push button signal? and the pin 3 output is the one make it off after given time out period?
You are right.

I used three 1N4148 D1, D2, D3 to isolated three input signals, so the three push buttons could trigger 3 different D-FFs, and used the falling edge of output (pin 3) to reset the D-FF, because the reset pin just needs trigger signal, so I used three caps to isolated the input signal when the falling edge was trigger then the reset pin will go back to their status after RC constant.

I didn't test the circuit yet, but I hope it won't has any big problem.

#### WBahn

Joined Mar 31, 2012
26,074
@vinras: I haven't seen a response to my query in Post #5 (perhaps I missed it). It seems rather important to know how you want the system to behave if a button for an LED is pressed while another LED is still lit and partway through its thirty second window.

#### ScottWang

Joined Aug 23, 2012
6,926
@vinras: I haven't seen a response to my query in Post #5 (perhaps I missed it). It seems rather important to know how you want the system to behave if a button for an LED is pressed while another LED is still lit and partway through its thirty second window.
There is one condition does not clear was the TS said:
when button 1 is pushed LED 1 will be on for 30 secs and then turned off automatically. If I push button 2 the second LED will be on for 30 secs

There are two conditions, the one is push the button 2 while the first led still light as you mentioned, in this situation, using one common 555 is impossible, the another condition is push the button 2 while the first led was turn off, in this situation, using one common 555 is possible.

#### vinras

Joined May 11, 2016
6
@vinras: I haven't seen a response to my query in Post #5 (perhaps I missed it). It seems rather important to know how you want the system to behave if a button for an LED is pressed while another LED is still lit and partway through its thirty second window.
@WBahn , sorry I have missed it, no I don't need to operate two buttons at the same time or during one of the out put is active, good example to think of is simple toy car gadget where if you push 1st button it will light up some police flashing light circuit for 10 (30) seconds, and the function of the second push button is to activate police siren for same duration, and push button 3 is to activate led running circuit etc. so I don't want to activate more than one at a time. I hope this will answer @ScottWang 's Question as well

#### WBahn

Joined Mar 31, 2012
26,074
@WBahn , sorry I have missed it, no I don't need to operate two buttons at the same time or during one of the out put is active, good example to think of is simple toy car gadget where if you push 1st button it will light up some police flashing light circuit for 10 (30) seconds, and the function of the second push button is to activate police siren for same duration, and push button 3 is to activate led running circuit etc. so I don't want to activate more than one at a time. I hope this will answer @ScottWang 's Question as well
So what do you want to have happen when, invariably, someone pushes the button to activate the police flashing light and then, five seconds later, pushes the button to activate the police siren?

The simplest is to say that people shouldn't do that and, if they do, then they can't complain about how the circuit behaves in response. This is known as "invoking undefined behavior" and it is sometimes (particularly in the software world) how these situations are handled. But if you are going to expect that, for instance, pushing the second button is simply ignored until after the time expires for the first, then you HAVE to explicitly include that expected behavior as part of your specification. Another reasonable expectation might be that the first button's action is immediately terminated and the second button then starts its action for the normal amount of time. There are other reasonable behaviors that could be specified. But if you choose not to specify what the expected behavior is, then you forfeit the right to object to whatever annoying behavior that turns out to be.

#### ScottWang

Joined Aug 23, 2012
6,926
How are the draw curent of these:
1. police flashing light
2. police siren
3. led running circuit

Two much draw current will be need the bjt or mosfet to drive them.

#### WBahn

Joined Mar 31, 2012
26,074
How are the draw curent of these:
1. police flashing light
2. police siren
3. led running circuit

Two much draw current will be need the bjt or mosfet to drive them.
I think he's just using that as an example to get the idea across.

#### ScottWang

Joined Aug 23, 2012
6,926
I think he's just using that as an example to get the idea across.
Maybe.