Hello eveyone, I'm trying to build a timer for a friend. He wants the timer to go for 72 hours and start/reset with a button. The issue i am struggling with is creating the timer circuit for 72 hours that is accurate. I've seen other posts using different IC's but a lot of them say that the accuracy isn't great for long hours. I know using a micro controller would be easier but he wants the timer to be simple, cheap, and small. If anyone has any expertise or help i would greatly appreciate it.

Thank you.

 

I know using a micro controller would be easier but he wants the timer to be simple, cheap, and small.

A microcontroller is simple, cheap, and small.

 

http://www.cypress.com/documentatio...5-implementing-rtc-psoc-4100psoc-4200-devices



$ 4 board to use for dev (size not to scale in pic) -

http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits

Button implement with onchip capsense.

Regards, Dana.

 

Welcome to AAC!

I know using a micro controller would be easier but he wants the timer to be simple, cheap, and small.

Define simple, cheap, and small.

 

Does he want to build more than one of these?

 

Quartz crystal oscillators are stable to a few ppm.
1ppm drift is like 1 second in 12 days.

 

A quartz oscillator with a frequency of 32 kHz provides good stability only at a stable temperature equal to the temperature at the inflection point (the top of the parabola) of the temperature dependence. Good quartz has this point about 23 degrees Celsius (if not mistaken), and this is the temperature on the hand (on average). To obtain high accuracy, frequency tuning is necessary, and for this, qualitative private measurers are needed. For a wider temperature range, much more frequent is needed. There are hourly quartz at a frequency of 4.19 .... MHz. Such quartz provides +/- 1 second / day in a very wide temperature range (under the condition of tuning). There are also radio hours that use the signals of special radio stations).

 

I know using a micro controller would be easier but he wants the timer to be simple, cheap, and small. If anyone has any expertise or help i would greatly appreciate it.
Thank you.

Do you need any indication that the clock is running e.g. a single digit 7 segment LED that tells the number of hours remaining? A LED that flashes every minute etc?

Is using CMOS DIP packages like 4060, 4040 OK for you or you can handle SMD to make it smaller?

Allen

 

Here is a clock, low power, using 32Khz watch crystal, ATTINY, and code.

http://www.microchip.com/wwwAppNotes/AppNotes.aspx?appnote=en591232

This spreadsheet shows the parts with onboard RTC module that you would use -

https://atmelcorporation.files.wordpress.com/2014/08/attinyavr-product-line_2014-08-20.gif


Regards, Dana.

 

Right at this moment I am building a stopwatch application using an ATmega48. If you need some help with a similar design on an ATtiny or ATmega just give me a shout.

 

72 hours is 259,200 seconds. With a 1-second clock period, this would take an 18-bit counter string to decode. One option is a CD4060 and CD4040 in series. As above, if you need high accuracy, then a crystal-based circuit using a CD4521 and CD4040 in series will work. Note that decoding the 72-hour mark will be easier if you can tolerate a 1.1% error in the 72-hour period (making it 72 hours 49 minutes). If not, the oscillator frequency can be adjusted, but then calibration becomes a problem.

ak

 

I've seen other posts using different IC's but a lot of them say that the accuracy isn't great for long hours.

So you want to be more accurate, but you haven't said how accurate. Do you need to be within 1 hour, 1 minute, 1 second, fractions of a second? The required level of accuracy changes everything.

Accurate isn't a yes/no question. You have to define the limit, the minimum level of accuracy that is acceptable, and then you can choose a circuit to match.

 

You have to define the limit, the minimum level of accuracy that is acceptable...

...and the operating temperature range.

 

How about this?

https://www.ebay.co.uk/itm/Multifun...322981046121?_trksid=p2349526.m4383.l4275.c10