battery operated digital clock

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hello friends,
i wish to make a digital clock.for display purpose i have plan to use seven segment display or 16*2 LCD display or led scrolling display(if there is any other convenient display method then please suggest me).The issue is that i wish to operate it using a battery.
Any one can suggest me a method or circuit to last battery for a long time as like in wrist watches(or like AA battery operated clock)..i expect all the suggestion on this project from you...all opinion,drawbacks and suggesttions are valuable for me.. thank you very much......

Last Edited: Thu. Jun 23, 2016 - 05:39 AM
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Just some random thoughts:

 

1) when you wake, bleary eyed, during the middle of the night it's far easier to read a clock that has 7-seg than one with an LCD display that usually involves having to press some kind of button to light a backlight

2) on the other hand 7-seg are current hogs and will quickly eat a battery (which is why most 7-seg based clocks are plugged it)

3) if you really intend this to be battery only then you probably don't really have a choice - it has to be LCD and an LCD that is readable even without a backlight (though having a switchable backlight for the night time event will be useful)

4) while your calculations may well show that the display device is the heaviest user of current you should do what you can to reduce the CPU current too. On the whole this means sleeping for as long as possible in the lowest power state possible.

5) modern AVRs, especially those with a model number ending in P (Picopower) are far better at working/sleeping at very low currents than the ancient old (10+ years) models of AVR. So avoid things like mega8, mega16, mega32, mega128 and concentrate on things like mega48P/88P/168P/328P or perhaps mega164P/324P/644P/1284P.

6) how big do you want this thing to be - what kind of enclosure? On the whole that will determine how much room you have for a battery. For example some very small clocks will only have room for something like a single (~3V) CR2032. If the clock is to be bigger perhaps there will be room for a couple of AAA, or maybe a couple of AA or even four of them? On the whole physical size is a fair indicator of capacity which is measured in AmpHours or possible MilliampHours.

 

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clawson wrote:
 7-seg are current hogs

You mean 7-segment LEDs are current hogs.

 

It's the fact that they're LEDs that causes the high current - not the 7-segment format.

 

7-segment LCDs are available.

 

Of course, for this reason, "led scrolling display" is going to be out of the question!

 

In the days of LED watches, you had to press a button to get the display to light.

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awneil wrote:
You mean 7-segment LEDs

I did indeed - I thought that was obvious - sorry if it wasn't.

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If you use one of the new oled style displays, they are very readable, and you can make it scroll inspiring fortune cookie sayings from Confucius as your Thought For The Day as you awaken to face challenges anew.

 

Imagecraft compiler user

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Bob,

 

But how do you see those in the dark? Are they backlit? If so what are the implications of that on battery life?

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They are real light emitting diodes. No backlight. There is a 'contrast adjust' reg that gives a little bright/dim range, and there is a 'display on/off' reg. I dont see how someone designing a twentyfirst century tech gizmo could use a twentieth century 7 seg numeric only display, whether led or lcd. Alphanumeric is much better. You can show words to the carbon based units. Maybe some clever screen saver with a walking pixel would be lo power enough for batt operation. But then one needs to sense when eyeballs are looking at the screen so the message can be lit up. An eyeball sensor! Yeah! Thats the ticket!

 

Imagecraft compiler user

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bobgardner wrote:

They are real light emitting diodes. No backlight. There is a 'contrast adjust' reg that gives a little bright/dim range, and there is a 'display on/off' reg. I dont see how someone designing a twentyfirst century tech gizmo could use a twentieth century 7 seg numeric only display, whether led or lcd. Alphanumeric is much better. You can show words to the carbon based units. Maybe some clever screen saver with a walking pixel would be lo power enough for batt operation. But then one needs to sense when eyeballs are looking at the screen so the message can be lit up. An eyeball sensor! Yeah! Thats the ticket!

How about a motion sensor? Detect when they moved to look at the display. Boom! Light it up!

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What's the power consumption like for OLED ?

 

For really low power, how about a so-called "e-paper" display?

 

aka "bistable" LCDs - as they are stable in both the "dark" and "light" states - don't need power to maintain.

 

Thus they take zero power except when they're actually changing.

 

https://en.wikipedia.org/wiki/Ch...

 

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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e-paper is great...except in the dark.

I think it faces the same challenges as an LCD, one needs a backlight to read it in the dark.

 

That means push a switch, swipe a screen, snap your fingers, etc., to trigger the backlight and display.

 

I have an e-paper "notepad" that my wife and I use to write notes back and forth, given our varying schedules.

 

JC

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DocJC wrote:
e-paper is great...except in the dark.

I think it faces the same challenges as an LCD

Yes, of course.

 

But then the same can be said of traditional clocks & watches with hands.

 

Achieving "Low power" is always a compromise ...

 

The OP didn't specify nighttime viewability.

 

In fact, the OP didn't specify much at all - just said,

 

i expect all the suggestion on this project from you

 

And hasn't engaged at all with any of the suggestions that have been made.

 

sad

 

 

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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Maybe a tritium light to shine on epaper?

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