First and foremost this is a School project but the teacher has highly suggested we use the internet to do this, this is also a group project in which i am the 3rd member.

My teammates have completed the basic design but the timing is still wrong and i have been assigned the job of designing a circuit that meets the following qualifications.

-Two push buttons
-One Starts/Stops the circuit much like a stopwatch
-Second button acts as an overall system reset

The project itself is supposed to resemble a timing control for a Boy scouts Model racing track, This is how the teacher described it to us.

I have included the Multisim file below and i mainly need help with designing the circuit that allows for starting/stopping/resetting

Thank you

I will try to post a picture soon

 

 

This is a blueprint i discovered through a Google search that is similar to what we are doing and it has a Stop/Start reset circuit built in but i don't know how to implement it properly!

 

So for a start/stop you just want to turn your clock signal On/Off from the 555. What if you came off the 555 Out and ran that signal into an AND Gate? You could use a push button to toggle a D flip flop for example. Push the button once and the Q output goes High, push the button again and the Q output goes Low. That Q output is one input to your AND gate, the other is your clock from the 555. When the Q out is High the clock pulses are passed to your counters, when Q is low nothing is passed to the counters. You can use a D flip flop configured as a divide by 2. The CLK into the flip flop is a single push button with switch debounce. As to the RST is just a matter of placing the 7490 reset pins to ground with a push button switch. There are other ways to go about this and my suggestion is merely something to think about.

I see you posted another drawing using different counters.

Ron

 

Hi Jacob,

Since this is a school project, it should be treated like a homework problem.

What are your ideas on how to implement reset and start/stop?

 

So for a start/stop you just want to turn your clock signal On/Off from the 555. What if you came off the 555 Out and ran that signal into an AND Gate? You could use a push button to toggle a D flip flop for example. Push the button once and the Q output goes High, push the button again and the Q output goes Low. That Q output is one input to your AND gate, the other is your clock from the 555. When the Q out is High the clock pulses are passed to your counters, when Q is low nothing is passed to the counters. You can use a D flip flop configured as a divide by 2. The CLK into the flip flop is a single push button with switch debounce. As to the RST is just a matter of placing the 7490 reset pins to ground with a push button switch. There are other ways to go about this and my suggestion is merely something to think about.

I see you posted another drawing using different counters.

Ron

The second drawing is, as i mentioned earlier, from a Google search i did on Start/Stop/Reset circuit. The counter in question actually works but i am really confused on how the switch works. I tried to implement a version of it for multisim into our Project but i don't understand how to get it working or which pins it would need to be hooked up to!

I understand the suggestion for using a D Flip FLop, to be honest i am surprised you explained it so gracefully. So give me a while and i will try out your suggestion and get back to you on whether it works or not! I didn't think that the reset switch would be that easy!

 

Hi Jacob,

Since this is a school project, it should be treated like a homework problem.

What are your ideas on how to implement reset and start/stop?

Well to be honest i really like how Reloadron Explained the usage of a D Flip-Flop to me and how combining it with an AND gate And a 555 timer on the other input. The biggest issue is that i suck at electronics!

 

I should have come to that idea on my own but this class has really been kicking my butt from the beginning!

 

Well to be honest i really like how Reloadron Explained the usage of a D Flip-Flop to me and how combining it with an AND gate And a 555 timer on the other input. The biggest issue is that i suck at electronics!

How do you want to implement those features? The suggested solutions aren't the simplest options...

If this is homework, we're not supposed to just give you the answers. Are you expected to do this on your own?

 

View attachment 84220

Why is the H input (which I'm assuming is the decimal point) being tied HI on the left counter and not the right? More specifically, why doesn't it need a current limiting resistor when the other segments apparently do?

Do understand why the 7490 chips are hooked up like they are?

Do you agree that it is okay to leave inputs unconnected?

 

So for a start/stop you just want to turn your clock signal On/Off from the 555. What if you came off the 555 Out and ran that signal into an AND Gate? You could use a push button to toggle a D flip flop for example. Push the button once and the Q output goes High, push the button again and the Q output goes Low. That Q output is one input to your AND gate, the other is your clock from the 555. When the Q out is High the clock pulses are passed to your counters, when Q is low nothing is passed to the counters. You can use a D flip flop configured as a divide by 2. The CLK into the flip flop is a single push button with switch debounce. As to the RST is just a matter of placing the 7490 reset pins to ground with a push button switch. There are other ways to go about this and my suggestion is merely something to think about.

I see you posted another drawing using different counters.

Ron

The problem with this suggestion is it is very susceptible to switch bounce. You pretty much always have to assume that whenever you activate a switch that it will actually open and close a few dozen times. You need debounce circuitry.

In general, using gated clocks is a bad idea unless you have a damn good reason (and damn good reasons DO exist).

 

How do you want to implement those features? The suggested solutions aren't the simplest options...

If this is homework, we're not supposed to just give you the answers. Are you expected to do this on your own?

I don't know where you keep getting the idea this is a homework assignment when i made it pretty clear this is a Group Project that i am the third member of, hopefully we have that settled now because i am in multisim at the moment trying to implement a D-FlipFlop! Maybe you should start from the beginning of the thread!

 

Why is the H input (which I'm assuming is the decimal point) being tied HI on the left counter and not the right? More specifically, why doesn't it need a current limiting resistor when the other segments apparently do?

Do understand why the 7490 chips are hooked up like they are?

Do you agree that it is okay to leave inputs unconnected?

I didn't design this particular part of the circuit, the other member of our group did. I don't know how to answer your question but i did think it was funny a pin was not being used on the 555! And i do agree that the way he has the 7490 hooked up is obviously done poorly but i can't fix that right now. I'm just trying to make a simple yet good circuit for starting and stopping the ENTIRE circuit on a whim, and of course a reset switch to reset the ENTIRE circuit.

 

I don't know where you keep getting the idea this is a homework assignment when i made it pretty clear this is a Group Project that i am the third member of, hopefully we have that settled now because i am in multisim at the moment trying to implement a D-FlipFlop! Maybe you should start from the beginning of the thread!

Perhaps because you posted in the Homework Help Forum???

The three people responding to this thread know how to solve your problem. But I'm sure your teacher doesn't care what we know... I suspect your teacher wanted you to do research on the internet, not ask for a solution.

 

The problem with this suggestion is it is very susceptible to switch bounce. You pretty much always have to assume that whenever you activate a switch that it will actually open and close a few dozen times. You need debounce circuitry.

In general, using gated clocks is a bad idea unless you have a damn good reason (and damn good reasons DO exist).

I Didn't know that Gated clocks were a bad idea, but to be honest this is just for a final project with two other group members, we don't plan on selling this as a commercial product nor does it need to be Quartz Accurate!

 

I Didn't know that Gated clocks were a bad idea, but to be honest this is just for a final project with two other group members, we don't plan on selling this as a commercial product nor does it need to be Quartz Accurate!

So that means that learning good design isn't important?

If you want your final project to behave erratically every time you push a button, then by all means proceed.

 

I don't know where you keep getting the idea this is a homework assignment when i made it pretty clear this is a Group Project that i am the third member of, hopefully we have that settled now because i am in multisim at the moment trying to implement a D-FlipFlop! Maybe you should start from the beginning of the thread!

If it is a project that you have been assigned and that you will be submitting for credit based on demonstrating something that you have learned or skills that you have, either individually or collectively, then it is Homework. Calling it a group project doesn't change that.

 

Perhaps because you posted in the Homework Help Forum???

The three people responding to this thread know how to solve your problem. But I'm sure your teacher doesn't care what we know... I suspect your teacher wanted you to do research on the internet, not ask for a solution.

I'm not asking for a solution Dude so please don't accuse me of being lazy, I didn't know where else to put my question as you guys don't have a "College Project help" Section.

I have been taking everything you guys have suggested and i am currently in multisim trying out the ideas, so unless you are willing to be helpful then please just don't waste either of our time!

Not trying to be rude!

 

I just thought i would ask for help because of my difficulty in this subject but i guess im better off not trying to...

 

I'm not asking for a solution Dude so please don't accuse me of being lazy, I didn't know where else to put my question as you guys don't have a "College Project help" Section.

I have been taking everything you guys have suggested and i am currently in multisim trying out the ideas, so unless you are willing to be helpful then please just don't waste either of our time!

Not trying to be rude!

The first responder gave you a solution that you're trying to implement. Though it is unlikely a solution that someone of your level would have come up with on their own.

I'd hate to see you if you were trying to be rude. You don't know me well enough to call me "Dude". Have a little respect for your elders. Were you taught that as a child???

If you'll answer my questions, I'll help guide you to a solution. But, as this sounds like a homework assignment, I won't give you an answer without you showing what you've attempted and what you understand.