Maker Pro
Maker Pro

Looking for help designing a timer

Robsta

Dec 30, 2017
4
Joined
Dec 30, 2017
Messages
4
Hi everyone,

I'm new here, I came specifically looking for help with a timer I need to make. It's been about 20 years since I did any real electronics, and even then I could construct circuits and PCB's but was never any good at designing them- so any help would be gratefully appreciated!

What I want to make is the following:

A timer with LCD display that will measure to at least two if not three decimal places of a second. It doesn't really need to measure in minutes, and definitely not hours.

I want to have count-up and count-down functions. When in count-down mode, I need to be able to set the starting time, obviously (say, 5 seconds, 10 seconds, etc), and also have an audible alarm/buzzer when the time reaches zero.
It would be nice on the count-up function to have a delayed start, with a buzzer sounding at the actual start point (i.e, press start, have a few seconds delay, then an alarm sound, then the actual timing process starts).

The above two features could be rolled into one with a count-down timer that allowed an over-run, and sounded an alarm at zero. That way, the delayed start could be set by the count-down with the over-run value actually being the count-up time- if that makes sense?

I also need to start and stop the timer with a foot switch, but I guess that is by-the-by. It would be better if this was optional, so the timer also had it's own start/stop switch, with the option to switch externally as and when required.

Could anyone point me in the right direction of a circuit that would do this? I already have a bench timer that supposedly does most of this, but it only measures to whole seconds, and when an external start/stop switch is connected, ALL of the devices buttons are disabled, so you have to disconnect the switch if you want to change the count-down time or even reset it. Stupid really. If I could somehow modify that timer to display in fractions of seconds, I'm sure I could re-wire the external switch connections to run off the device buttons, thereby bypassing the lock-out of all the other buttons- this would probably be the easiest option, rather than starting from scratch, but again I have no idea how I would go about altering the timer resolution.

Many thanks in advance everyone.
 

Bluejets

Oct 5, 2014
6,073
Joined
Oct 5, 2014
Messages
6,073
Stop watch has many of the functions.
Maybe hack one of those.
For $5.00 I'd say worth a try.
 

kellys_eye

Jun 25, 2010
5,311
Joined
Jun 25, 2010
Messages
5,311
A timer with LCD display that will measure to at least two if not three decimal places of a second.
Do you need that accuracy? Seriously?

Look to find a digital frequency meter with TIMING function (many have this) as they also have external trigger (start/stop) inputs too and can, by their nature, be as accurate as the clock-derived crystal frequency reference built-in to them.

Here's a counter/timer on eBay current at $50

https://www.ebay.co.uk/itm/Racal-Da...409770?hash=item36284d9faa:g:wIcAAOSwdx1aO7qh
 

Robsta

Dec 30, 2017
4
Joined
Dec 30, 2017
Messages
4
Thanks both.

Modifying a stopwatch may be the simplest and cheapest way to go about it. I hadn't actually thought of that, so I'll look into it some more.

Yes I definitely need two decimal places at least- it's going to be a speed-shooting timer primarily, and it's that critical (for example, I'm typically shooting the round under 6 seconds, but more than 5; registering a time of 5 seconds would be unfair as I'm closer to 6 seconds, but registering 6 seconds could lose me the top-spot).

I was hoping to do this fairly inexpensively, but if the stop-watch idea doesn't pan out, there's a higher-resolution stop clock-only timer similar to the one I've already got which is only £10, so I might just use the pair in tandem; use the stop-clock operated with the footswitch (which will solve the problem of the buttons being disabled- there are no other buttons on this model), and use my existing timer for count-down only, manually operated. It's not as convenient as I would have liked, but it only means spending an extra tenner.
 

Robsta

Dec 30, 2017
4
Joined
Dec 30, 2017
Messages
4
How does one determine the timing resolution?

I was just thinking that maybe I'm over-thinking this; the timer I have has all the features I need, bar the resolution (and the issue with the buttons disabling, which I think is an easy fix)- all I need to do is increase the resolution (and/or the display), whether that be by altering the existing circuit, or copying it and replacing whichever component determines the resolution.

Is it really this easy, or am I missing something?

Thanks again all.
 

AnalogKid

Jun 10, 2015
2,688
Joined
Jun 10, 2015
Messages
2,688
the timer I have has all the features I need, bar the resolution (and the issue with the buttons disabling, which I think is an easy fix)- all I need to do is increase the resolution (and/or the display), whether that be by altering the existing circuit, or copying it and replacing whichever component determines the resolution.

Is it really this easy, or am I missing something?
You're missing something - the changes you listed add up to a significant modification of an existing product. But you have given us literally zero information to work with.

Schematic of "the timer I have"
Photos inside and outside

How does one determine the timing resolution?

That one is easy - you tell us how many digits you need before and after the decimal point.

ak
 

Petkan

Feb 9, 2011
19
Joined
Feb 9, 2011
Messages
19
How does one determine the timing resolution?

I was just thinking that maybe I'm over-thinking this; the timer I have has all the features I need, bar the resolution (and the issue with the buttons disabling, which I think is an easy fix)- all I need to do is increase the resolution (and/or the display), whether that be by altering the existing circuit, or copying it and replacing whichever component determines the resolution.

Is it really this easy, or am I missing something?

Thanks again all.

Timer's resolution is defined by the frequency counted. For instance a timer counting 1MHz has 1 us resolution.
For instance 1 MHz may be derived from 16 MHz crystal oscillator. It this clock is say 0.01% so is the timer
 
Top