Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need help making a simple pop-up timer

Not open for further replies.


New Member
Hi, I'm trying to create a simple pop-up timer for a science experiment but don't really know where to start.

**broken link removed**

My idea is basically for a small timer that retracts after a set countdown.

It's for pushing an external button for a very precise amount of time. I want to be able to control the countdown to within a hundredth of a second and to be able to reset it easily. If there was a way to put the timings into memory (like in a calculator) that would be ideal.

How it would work is, I set the time in the timer, and push the trigger button down onto a button which starts the countdown. When the countdown is finished the arm extension would pop-in, disengaging the external button.

The design does not need to be as above, but I would like it to be small and able to fit in and be worked with one hand.

Is this something that could be done by an amateur like myself or would it take considerably more skill? If it's the former, can someone give me some advice on where I can get started?

Does a timer like this already exist? If there is I might prefer to just use that.
Last edited:
Sounds pretty cool. Is this to be used for winning a competition or something?

I hope it's not for playing the poker machines, that's only a myth that pressing the button for an exact time causes a winning roll.
It's not for poker, in fact I'm not really sure how it would work for poker...

It's my own experiment to use with a machine to guide a target into a hole.

I'm not even sure it would work, but it should be fine in theory.

Thanks for the confidence in the concept, if anyone could provide help on where I should get started it'd be appreciated.


I'm thinking of trying to utilize a 555 Timer circuit with a spring loaded button.

Perhaps I could butcher a Turkey timer for its parts, unless there's a better alternative.

I'd much rather the button itself be at the tip of the timer so the compression is what starts it, but I'm not sure how I could do that...

Still not sure about what sort of digital timer I should use.
A 555 timer won't be 'that' accurate. Tolerances and temperature variations won't give you a decent resolution.

At 0.01 seconds (10ms) it'll be tough, I'm sure the elecotrnics own't be too difficult but you might have to tweak the timings for any delay caused by the 'retract' mechanism. Also, if it is holding the button down for a certain amount of time, then you'll have a small delay at the start too, between starting the timer and the plunger actually fully depressing the button. Those variables shouldn't change too much though, so they could be 'hardwired' with a calibration.

I can give you idea's on the plunger mechanism, although that would take the fun out of your science experiment :) As for the pure logic would work, but you may end up with lots of chips in there, although they are cheap and don't require programming. Even harder to add memory to that. Sounds like a perfect application for a microcontroller, but I'm not sure if you want to get into that :)

So I guess using an off the shelve one is the best idea, hacking it for your needs. A countdown timer would be great, as long as it has an alarm which you can 'tap' to get a signal out of it when it hits 0...but...can you get egg timers where you can set the resolution to 10ms ?
Well that's the primary problem methinks.

There don't seem to be commercial timers (that I can find) that deal exclusively in seconds. They all have minutes and those I've found only allow you to adjust the minutes. Even if I found one that let you adjust the seconds, that probably wouldn't be precise enough.

A 100dth of a second may be asking much, but even a 10th of a second seems hard to come by. I'm not even sure what search terms to look for to get the results I want...
Ahh, so you don't require a timer with minutes? Just purely seconds (like 0-999) along with tenths and 100ths ? That makes using logic gates easier!! As you don't have to fiddle about with reseting the counting at 60. Of cousre I 'say' it makes it easier, but I have never tried making one from scratch...too many microcontorllers sitting around my place doing nothing. I may look into this, and see what is the easiest route as I haven't managed to find any commercial products working with franctions of as second.

I did manage to find some 'kits' which count in seconds (no mintues just up/down 0-999) some even used 10th's as well, but they appeared to be a bit expensive ($60 US).
Well I'd prefer not to have to make one from scratch, since the design of the device itself is enough work.

Yeah, it doesn't need minutes at all. In fact if it only went up to 60 seconds it would be fine, so long as I could adjust it beyond just seconds.

Is there a simple way to build that logic gate? I was thinking of just using a market timer but since it doesn't seem to exist I may just have to make my own. Would it be possible to reprogram a regular timer to fit my purposes? Or easier just to build it from scratch?
Well, I realise that making it from scratch, especially using gates relaly is a hassle. Even though these chips are pretty cheap, you'll need a few of them, and, even though they don't require many uspport components (resistors, capacitors) they require lots of connections.

If you were dealing with non decimal counting, like minutes (go up to 60, rather than 100) then I probably would have abandoned the idea. But, there are chips specifically for counting 0-9, then reseting (CD4510, 74HC4510 etc..). Look here:

**broken link removed**

Alotof circuits there deal with 0-60, which you don't need. In fact, the chips can just be cascaded, one for each digit.

As always tohugh, things get tricky. With a 100Hz input, you could have 100ths, 10ths, seconds, and tens of seconds. The chip can count up or down, and has an output when it resets (when it over flows from 9, to 0, or 0 to 9). You'll need an accurate clock for this, preferably crystal. One last thing, thes chips have 'loadable' presets, meaning you can load in a preset value, allowing you to reset your counter to a specified time, but, for four digits, each one takes 4 lines, so thats 16 lines to pull high/low for the reset. Its starting to get complicated :/

I'm sure there is a chip which can do this all for you, although, as you found out, commercial products, and the chips that drive them, all seem to work in seconds and minutes, with no smaller resolution. I'll keep looking.


The ICM7217, and the ICM7217A both count 0000-9999 (up or down), but differ ein the display they use. If you check the datasheet out, you can see the connections required. This will do almost all of the work for you, all you'll need is 100Hz source, and some switches for the 'preset count'. I ithnk it even has a 'store' function for reseting to a set time after its hit 0.

Note: Maxim are great for providing samples. You sohiuld be able to get free samples of this (or any other one of their chips) within days :)

You're amazing!

This will finally put me on the right track. I don't know much about building circuits, but this is a start.

Thanks, I'll know who to go to when I reach my next step.
Most welcome :)

Hope you get it all going, and we're all here if you get stuck.

Apologies for the horrific number of typo's in my above posts...they were rushed.
Have you considered a microwave oven PCB, with a digital readout? Many ovens I disassemble were unusable, but the logic board can be adjusted to your needs. Just change the crystal frequency and bypass the bell for a plunger ( solenoid). The front face has extra keys, but with changes can be set to fractional readouts.
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips