Instructables

How can I build a small digital counter powered by solar panel?

I would like to make a small digital counter.  The requirements are:

1. No bigger than 2" x 1.5" x 1"
2. Powered by small solar cell (like those calculators we had in elementary school).
3. Has 4 buttons that adjust the counter; +1, -1, +5, -5.

The solar powered part would be neat, but not a must have.  The goal of this device is to be used as a counter for gaming applications d&d hp counter and the like.  The dimensions are small because ideally I would be able to place these on a card, character sheet, grid representing a map to track both the number on the counter and the location of the counter.  If it is reasonable I would like to have a much smaller device than my original goal of  2" x 1.5" x 1".  I have a bit of experience wiring small project on a breadboard and I'm confident I could throw something small together from schematics.  The last thing is that I would like to make a number of these, so cheap is good. What I don't know is:

1. Where can I find such a small solar panel?
2. Where can I find such a small digital display counter (2 digits minimum, probably don't need more than 3 digits)?
3. Is there open source software I can use to model a simple circuit and test my schematics before trying to build it?
4. Tips for creating a small circuit board in the event one is required.

This is not a hobby area I have explored much so I may not be using the proper terms and this project may not be feasible so please forgive me if you find this to be a silly request.

Thank you for your time.

Apart from the solar panel/charger this should be a relatively simple project as both counters and binary to 7-segment decoder functions are available as single ICs.

You can use an 8-bit counter IC to deal with incrementing/ decrementing the number up to 255, although I'm not aware of a proper way to increase the number by 5 (one way to do it is to leave the +/-5 switches without debouncing circuits- inaccurate but easy).

You may be able to find a suitable decoder that'll do the 8bits to 3 digit conversion in one go, but it is more likely that you'll have to stack a few smaller ICs together to get the right results- have a look and see what other people have done, it should be a fairly common circuit.

As for low power displays, make sure to get individual digits, or a single package which can be staticly driven (so you don't have to worry about lighting each digit one at a time and switching between them at high speed). Self magnifying displays can be very low power, which will be important if you add a solar panel later- for example I have 3-digit ones here that are just over 1/2" long and only need 7mW per digit.

If you really want to add a solar panel, I would still build them with a rechargable battery and see if you can find a suitable solar panel that'll put out a slightly higher voltage while you are looking for the other parts.
A small solar panel like that may not work. But you could use a button battery.

Start checking out major parts distributors like Mouser.

Do a web search. You can find all sorts of 'small electronic counter schematics' out there. Most of then use a simple pic micro controller and a pair of 8 segment displays to display the numbers. If you want to move it up to an LCD you'll need to make sure the LCD comes with it's own driver and then adjust the programing on the pic to work with the driver.