Newb Help

I want to create a watch that has a binary display for the time and date. I was wondering what would be the best board to use to create a compact and light watch that will draw minimal power. I don't want to have to charge this watch every night. I was also thinking possibly some wireless interaction where it will poll for a connection and update the time. I'm extremely new to this but I'm not afraid of the programming aspect. I just want to know exactly what is needed for a noob to pull this off. I've seen a couple of projects but nothing specifically what I want.

Thanks for any help :]

You should probably figure out the coding and hardware requirements for a larger device, first. When that works, you can determine how to miniaturize it.

Hour ranges from 0 to 23 (or 0 to 11 if you have AM/PM indicator). That will need 6 LEDs.

Minute ranges from from 0 to 59. That will require 7 LEDs.

Second ranges from 0 to 59. That will require 7 LEDs.

That is between 13 and 20 LEDs. The Arduino has 20 digital pins (2 of which are for the serial connection, if you are using that (and you will for debugging and uploading sketches, most likely).

I was also thinking possibly some wireless interaction where it will poll for a connection and update the time.

Poll what? Wireless and long battery life (especially in watch size) are not compatible concepts.

I just want to know exactly what is needed for a noob to pull this off.

By the time you are done, you won't be a noob, that's for sure.

A small LED matrix display that you scan would not need so many pins. Like:

Other: LEDs take a lot more power than LCDs.

Some early LED watches saved power by blanking the display until you shook your hand...

Or maybe use a small graphics display instead?
I picked up one of these, haven’t tried doing anything with it yet.
Even has some sample codes posted.

I know that wifi isn't the best for battery but if it is only polling the internet once a day/month/whatever it wouldn't be that bad. It would query a website to keep the time correct. I was also thinking of some interfacing with my android phone. Would the LCD screen draw a great deal of power? that would be pretty awesome to have. I could have it turn off after like 15-30 seconds and turn on by pressing a button.

If I were to stick with LED's I would display Hours Minutes and the Date. I don't know if I would display the seconds. Or I can do all that and when you click a button it displays the date.

As I said I'm pretty noob so I'm not entirely positive how feasible all these ideas are.

From page 25 of the datasheet, it looks like the display itself uses 2-3mA, while the backlight needs 20mA.

Back to your original post: "a binary display for the time and date", "display Hours Minutes and the Date" So you'd have 4 LEDs for minutes-ones (0-9), 3 LEDs for minutes-tens (0-5), 4 LEDs for hours-ones (0-11), 4 LEDs for days-ones (0-9), 2 LEDs for days-tens (0-3), 4 LEDs for month (0-12)

Total: 21 - 1 too many for a '328 unless you do some multiplexing; 4 pins for the bits, 6 for the digits. Down to 10. Need 2 for serial interfacing to USB/Serial device for occasional internet connection. Think I'd go with RTC chip via I2C instead. Leaves you free 8 free for android interface and display turn on button.

okay so what I have gotten from that post is an lcd screen is not a good idea because of the backlight. (unless you werent talking about the lcd screen there).

I also follow how many pins I would need. I don't entirely get multiplexing but I'm sure that's something I can Google and learn more about.

With the 8 free pins would I be able to have like a message warning or something like that? And that leaves enough for a button to press to turn on the display.

I have two questions, the first about what you said with the serial interfacing... Do you mean the wireless chip/a usb updater type thing?

and is there a battery that would sufficiently give me an extended period of time without needing a charge/ a solar charging way / is a normal battery probably what I'm ending up with?

Thank you for your help that was a very specific and straight forward response.

You could do whatever you'd like with the free pins - maybe use them to enter an alarm time or something, have all the LEDs flash on/off to let you know it went off. Serial - I was thinking some pins/connector so could connect to USB/Serial adapter to download sketches or something. Keep D0/D1 free for that. Battery - how's 1000mAH LiPo battery sound? ATMega running 8 MHz, 3.7V, draws about 5mA, LEDs however bright you have them running. at 4 MHz, 1.2mA. Go to sleep in between the minute updates, draw even less.

I am sorry I am not an engineer and no skill at electricity. Can you give me an estimate of how much time that would be?

I am a programmer so that part really doesn't scare me too much. I take that as a challenge.

I greatly appreciate all of your help you have been great.

Do you want a binary display, or a BCD display?
If the latter, you use fewer LEDs and possibly pins.

I'm pretty sure I'm going with BCD but can you elaborate on it saving me LED's. 59 is 6 LED's (1 less then BCD) 12 is 5 LED's (3 less then BCD) right?

It has been a while since I did binary and BCD

Here’s a binary LED display - you have to look at the Bits and interpret them.

That looks more like BCD than binary. 0 to 59 in BCD needs 3 + 4 bits, but only 6 bits in binary.

4 bits is pretty easy to look and interpret, 6 bits much harder. I think even 12 is pushing it, but you gotta draw the line somewhere on the size. 6 'digits' seems reasonable, especially with month rarely changing and Days only changing 7 times a week.

I do understand what you are saying it is much easier to convert 0-9 and 0-5 to binary then 0-59. But whatever is more compact and cleaner I guess would be the best for me. I'd like to get insanely good at binary :]

Hi, Here's an example.. Not much detail, though:

Ok, so 4 digits then? Minutes 0-59 Hours 0-23

Days 1-31 Month 1-12

Or do you want to go day of the year? 1 digit, 1-366?

Or 1 digit, minute of the year? 1-527,040? 20 LEDs


That one actually gave me the idea however it wasn't exactly what I wanted and as you said not very in depth.

CrossRoads: Or do you want to go day of the year? 1 digit, 1-366?

Or 1 digit, minute of the year? 1-527,040? 20 LEDs

I don't want the day of the year or the minute of the year. A basic 0-23 hours 0-59 minutes 1-31 days and 1-12 months is what I'm looking for. I wouldn't even mind pressing a button and having the time turn to the date and flash back after 15-30 seconds to conserve on LED's being used.

About LED vs LCD screen is LCD really less energy? I've always thought LED's consumed far less energy then anything else. That's why they have LED LCD tvs or am I thinking to large scale? Because I really wouldn't mind an LCD display, that would actually be pretty awesome because then I can just work on linking it to my phone once I get it all setup.

so if you have any suggestions on boards, LED's/LCD displays, batteries, or whatever else you can think of feel free to note it I'll go through and do my best to patch together a decent combo. I'll probably ask for the groups opinion on my selection just to be sure.


Please clarify what you want to see when you look at your wrist. You said binary to start with, said you wanted to get good at converting. I posted a schematic for you, suggested a nice battery, you indicated you wanted a coding challenge so I left the multiplexing of the display, doing a serial interface to update time, provided some buttons for setting time, alarm, turning on display temporarily, whatever. Here's a high brightness LED that is small and would need very little current to be nice & bright even.

Now after 2 pages of discussion over several days, you are waffling about what the display should be. Go poke around here, see if anything suits your fancy.

Sorry for switching back and forth I'm just considering all the options I have.

I think for now I'm going to go with the LED's maybe in the future when I know a bit more I'll play around with an LCD graphics display. To have a solid example.

So I will end up with the 1000mAH batter that CrossRoads suggested. Would the RGB LED's draw the same amount of current or more/less then just a straight one color LED? Kinda like this one:

Does 5mm look much larger then 3mm in an LED? I feel like it won't be a significant change but also that they might stick out more. Anyone know from experience of how it aesthetically would look on a watch?

I like the LED suggested I'm just perusing other possible options that way I'm not restricted to one color. However if it draws more power or would look too large on a watch then I am perfectly fine with just one color.