basic elapsed seconds counter

What sort of accuracy do you need and how long will the timed period be? (In other words, do you need "watch" accuracy, or within a couple of percent, and how many digits will be needed to display the timed period?)

The timing is relatively easy, depending on accuracy and the length of the timed period, but the display will take a bit more work.

For an LCD display, you would need a micro-controller, along with programming skills, a compiler and a programmer and, of course, the other hardware such as resistors, capacitors, diodes etc. Programmers and compilers can cost a fair bit. Then you'd need to spend a bit of time working up to the level you require. This method would provide the best results, both in timing and quality of display, but is by far the most expensive, especially if this is a small project.

LED displays are simpler, but need a few more chips for counting, decoding and LED display segment driving, dependent on the number of digits. One thing to consider is whether the unit will be used in relative darkness or daylight. LEDs are best for darker settings and LCDs are more suited to lighter environments.

A bit more info would help. ... Steve

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Thanks for the reply Steve, A bit more info... The accuracy is not an issue for me so long as it is 'fairly' accurate. The only thing I can liken it to is when you step out a distance- "right, that's 20 metres give or take a couple.". A maximum time to count to would be 99 seconds. I have read a little about the

555 timer so I think that's my guy, but as for how I can use it for this application, I'm stumped.

I also like the suggestion for a couple of segment LCD's to display it. I hope this is enough info to get me started. Thanks again!

I just had a wacko thought. Go to your nearest drugstore, Radio Shack, or whatever, and pick up a cheap stopwatch built into a fairly large case.

Build yourself a little "button pusher" -- maybe a reed relay circuit

-- driven when you want to start and stop the timing. Perform a little microsurgery on the stopwatch to solder your button pusher across the stopwatch's start/stop button.

Voila!

Tom

--
This will work: (View in Courier)


   [7555]---[4510]---[4510]
              |        |
   [7555]-+-[4543]---[4543]        
          |   |        |
          +-[7SEG]---[7SEG]

Do you need a schematic?

Or maybe one of those cheapo clocks (wristwatch or little giveaway types) and see what happens if you disconnect and reconnect the battery... if it starts countng seconds from 12:00:00 you are all set!

Back in the Olden Days when 4-function calculators first started to become cheap, there were magazine articles on using them for counters by faking a keypress. You might be able to use the output of a 555 to provide the pulse, and just use the calculator as the counter.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

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Hi John,

Yes- a schematic would be great! Just looking into it now can you correct my logic?

7555 (provides timed pulses)-----4510(converts pulses to binary code)-----4543(converts binary code to drive 7 seg)-----7 seg(displays 4543 input). A couple of questions:

-How can you set the 7555 to count seconds?

-How can this be reset before each count?

-How on earth can I build it???? Very keen to learn about this frontier! Thanks for the assistance

The circuit given, with an oscillator, counters and 7-segment drivers, is the most straightforward. However, FYI, I think most people today would use a small microcontroller instead. That does not mean I'm suggesting you try that approach now, given your lack of experience. I'm simply planting a seed for consideration down the road, should you find yourself becoming more interested in things electronic.

This approach would use a microcontroller (around $2) to do the job of the oscillator, counters and drivers. You could also get fancy and wire in some buttons, a flashing LED or two, etc etc.

Mike

Depending on what else you might want to do, here's a device that I've found handy for counting elapsed seconds with a minimum of muss & fuss:

JM

Thanks Mike. It appears a microcontroller combines all tasks into a single unit, and $2 is plenty cheap enough. But what makes this method more complex? Do I need computer programs etc to program it? Thanks for the suggestion

Hi John,

Thanks for the link, I will check it out now. Simple and straigthforward sounds appealing... I will post back with any questions if that's ok. Cheers

I'm sorry John, but this module is too expensive. I would like to keep the cost to

1) It requires knowing how to write software for the device. 2) It requires understanding the device hardware (timers, I/O ports, etc). 3) It requires a toolset. This can just be a free assembler program for your case. 4) It requires a way to download a program into the micro. This can be a simple parallel-port programmer, or a USB-based device.

None of this is particularly complex, but it's certainly not as easy as wiring up 5 small chips.

For the price of this added complexity you get corresponding benefits, the biggest of which are the ability to add functionality without adding much if any hardware, and to quickly and easily experiment and modify the functionality, to tweak the design. It can also be a heck of a lot of fun.

Mike

Do you know of any resources which can help me learn about microcontrollers? I am also still very interested in wiring up 5 small chips however...

avrfreaks.net and 8052.com are two sites that come to mind. They have forums, tutorials, etc.

Mike

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Hi John,

Thank you very much for your help. However I am unable to get your schematic (I have been at it for 2 hours!). Is there another place where I can access it? Perhaps email? Thanks again -Ben