# Need Help for timer.

#### asanenga

Joined Oct 14, 2015
1
Hi everyone Im new started doing electronics engineering at college i have this design a digital stop watch using discrete elements
Functions: Start, Stop, Reset.
• Should be able to count up and count down.
• The interval time should track the minutes, seconds and tenths of a second. Ex. 3:45.8 would be 3 minutes, 45 seconds and 8 tenths of a second.
• The max interval (up or down) will be 9:59.0 after which watch should reset to 0:00.0
• The design may be done using available logic devices or using programmable logic devices (PLDs), but no microcontroller
all the circuits i have seen so far are using micro-controllers

#### Dodgydave

Joined Jun 22, 2012
11,257
One solution,,, you're going to need to use cd4510 bcd counter, cd4511 bcd to seven seg driver, and a 10hz clock source, say a 555 timer or cd4093 osc, and logic gates to send the reset pulse to the last counter..

ok now start googling....

#### AnalogKid

Joined Aug 1, 2013
10,951
Why does a stop watch have to count down? This makes the overall circuit design much more difficult.

ak

#### ISB123

Joined May 21, 2014
1,236
Why does a stop watch have to count down? This makes the overall circuit design much more difficult.

ak
Because engineer is supposed to be a problem solver.

#### shteii01

Joined Feb 19, 2010
4,644
Because engineer is supposed to be a problem solver.
"rumors and lies."

#### JoeJester

Joined Apr 26, 2005
4,390
Why does a stop watch have to count down?
NBA and NFL both use multiple countdown timers.

#### AnalogKid

Joined Aug 1, 2013
10,951
NBA and NFL both use multiple countdown timers.
True, but I doubt that they are on this forum asking how to build them from scratch. There is nothing in the original post to indicate that the question is fully formed. A bidirectional modulo-6 counter is not an off-the-shelf chip.

ak

#### JoeJester

Joined Apr 26, 2005
4,390
@AnalogKid I doubt they are here either ... The TS never indicated the use.

#### WBahn

Joined Mar 31, 2012
29,888
Why does a stop watch have to count down? This makes the overall circuit design much more difficult.

ak
I've owned several watches that had countdown timer. You can set it for a specific time and then it buzzes when the time expires. Very useful.

#### WBahn

Joined Mar 31, 2012
29,888
True, but I doubt that they are on this forum asking how to build them from scratch. There is nothing in the original post to indicate that the question is fully formed. A bidirectional modulo-6 counter is not an off-the-shelf chip.

ak
So... engineering students should only learn to solve problems for which there are complete off-the-shelf solutions available?

#### AnalogKid

Joined Aug 1, 2013
10,951
So... engineering students should only learn to solve problems for which there are complete off-the-shelf solutions available?
Revealing, but not even close to what I said.

My point is that a project should be analyzed for its practicability early in the design cycle, so bottlenecks and other schedule drivers can be evaluated/challenged/negotiated. I was doing the TS a favor by pointing out something he does not have enough experience to realize on his own, that one part of one sentence in his project description is a bigger deal than he realizes, and he might save himself some grief if he confirms that it is necessary before starting to solve it.

In the late 70's / early 80's I bought a floor sample digital watch with a countdown timer from Casio at the summer CES. Wearing it right now.

ak

#### WBahn

Joined Mar 31, 2012
29,888
The project would be a lot simpler if it only counted integer seconds and didn't count minutes or tenths of seconds. Are you recommending that the TS confirm that these are really necessary before starting to solve it?

The TS was given a set of specifications for a course assignment. It's pretty explicit that it needs to count up and down in order to meet spec. That it counts down is referenced numerous places in the requirements, so the chances that the assignment didn't mean to require the project to support being able to count down are pretty much that same that the assignment didn't mean to require the project to support minutes or tenths of seconds -- namely basically zero.

#### GopherT

Joined Nov 23, 2012
8,009
The project would be a lot simpler if it only counted integer seconds and didn't count minutes or tenths of seconds. Are you recommending that the TS confirm that these are really necessary before starting to solve it?

The TS was given a set of specifications for a course assignment. It's pretty explicit that it needs to count up and down in order to meet spec. That it counts down is referenced numerous places in the requirements, so the chances that the assignment didn't mean to require the project to support being able to count down are pretty much that same that the assignment didn't mean to require the project to support minutes or tenths of seconds -- namely basically zero.
What's wrong with you today? Your arguments are not aligned with reality or common sense.

#### WBahn

Joined Mar 31, 2012
29,888
What's wrong with you today? Your arguments are not aligned with reality or common sense.
Please explain. Are you saying that is IS common sense to ask if the assignment really does need to count down as well as up? Given how explicit the instructions are, how is that reasonable? And, if it IS reasonable, how is it not then reasonable to also question every other part of the specification?

#### GopherT

Joined Nov 23, 2012
8,009
Please explain. Are you saying that is IS common sense to ask if the assignment really does need to count down as well as up? Given how explicit the instructions are, how is that reasonable? And, if it IS reasonable, how is it not then reasonable to also question every other part of the specification?
What I'm saying is, there is never any harm in asking a customer to clarify their needs. If you see a big expense with questionable added value, there is nothing wrong with discussing that specific point in detail to make sure the customer understands that a rarely used function could double the development cost.

From the OPs description of the project, the phrase can be interpreted that it is an assignment imposed by a professor OR it is a design project with a list of objectives that are self-imposed.

Hi everyone Im new started doing electronics engineering at college i have this design a digital stop watch using discrete elements
If imposed by someone else, there is little to be done. If self imposed, then the OP could rethink their priorities. Even if a professor made it an assignment, I would be happy to be alerted about a possible challenge associated with the countdown timer portion of the project.

In either case, your ability to bust into a conversation and belittling someone else's line of questions doesn't make me want to have a beer with you.

#### JoeJester

Joined Apr 26, 2005
4,390
If this was a self imposed project, the TS picked it from a list. I doubt they thought of all those specifications.

#### WBahn

Joined Mar 31, 2012
29,888
doesn't make me want to have a beer with you.
That's fine. The best thing to do with beer is pour it back into the horse it came out of, anyway.

#### WBahn

Joined Mar 31, 2012
29,888
What I'm saying is, there is never any harm in asking a customer to clarify their needs. If you see a big expense with questionable added value, there is nothing wrong with discussing that specific point in detail to make sure the customer understands that a rarely used function could double the development cost.
Okay, so why not question the need for tenth-second resolution. If we are going to assume that being able to count down is a rarely used function that the customer needs to justify, why can't the same be said for the ability to get tenth-second timings?

And shouldn't the requirement for ten minutes be questioned, too? That knife cuts both ways. Shouldn't the customer be made aware that a ten-minute limit might often not be sufficient and should perhaps be increased?

Discussing specs with customers is fine and, in the educational setting there are plenty of opportunities for this in project and capstone courses. But this is an assignment. There's a difference.

#### AnalogKid

Joined Aug 1, 2013
10,951
There also is a difference between more or less resolution/precision in a fundamental function, and whether or not to include a electronically very different function (up/down counting vs. up-only counting). Also, it doesn't take a degree in industrial engineering to know that timing human events benefits from 0.1 s resolution. If the requirement were for microsecond resolution, I'd question it vigorously (as I am right now in another thread.).

And again, there was something in the OP wording that raised a should/shall question in my little brain.

ak

#### WBahn

Joined Mar 31, 2012
29,888
And again, there was something in the OP wording that raised a should/shall question in my little brain.
I don't see it, but I will certainly allow for it. If you read the OP as being a proposed set of specs as opposed to a statement of an assignment, then it becomes much more reasonable to query about the need for some of the specs.