I'm looking to build a belt clock on the pager form.
The specs are pretty simple -- HH:MM:SS and DD:MM:YY, pretty simple.
The device will be battery powered with LED display like this: **broken link removed** I'll hafta attach an additional 2 digit display for the seconds, unless there is a 6 digit display about .28" tall going around. (Those 4 digit ones are the only ones I can find)
This can be done, heck if the **broken link removed**, then I can do it. I'm thinking that I might have to use a cellphone battery if power supply is a problem. It'll have to be opened to adjust anything (to make it as water resistant as possible). An aluminum case (probably anodized to a cool dark blue) with a TIG welded belt loop, and we'll figure out how to program the microcontroller so that the date is displayed every 15 seconds for a duration of 2 seconds.
Now, how do I rig up the electronic circuit? What microcontroller with real time clock circuit (crystal)? I see many like this, but they're all AC powered. I don't think battery backup will be required or could fit. I'm thinking that I might also like a 5 LED battery charge circuit which comes on for 3 seconds every minute.
No, I'm going for a completely different, unique device.
According to the specs, it requires 1.8v at 20mA (per chip: not sure if that means per digit or per 4 digit display). That equals .36 watts. A cellphone battery may be around 3.6 volts, but I don't know how long it would last -- a week?
If that cellphone battery is rated for 1000mAh (an average, some cellphone batteries are less, some are a bit more) @ 3.6V then a circuit drawing 0.36W should (very roughly) run for about 10 hours.
However, that's assuming 100% efficiency , wich is impossible. Using resistors in series with your leds straight from 3.6V will waste a lot more power - so you'll have to use some switching regulator to lower the 3.6V closer to the 1.8V required by the leds. Even then, some power will be wasted.
No, I'm going for a completely different, unique device.
According to the specs, it requires 1.8v at 20mA (per chip: not sure if that means per digit or per 4 digit display). That equals .36 watts. A cellphone battery may be around 3.6 volts, but I don't know how long it would last -- a week?
The best way to save current is to multiplex the display so only one display is lit at a time. However, each led will have to be driven with maxium current, otherwise the display will become very dim.