Miniature Numeric Display - Is it possible?

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uncalled1st
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Miniature Numeric Display - Is it possible?

Post by uncalled1st » Sun Apr 06, 2008 8:01 am

I'm trying to find a way to make a small numeric display device with at least three digits, ideally five, to display numbers in increments of 50 (or 5 with a smaller display). Display would be on top, with tiny buttons on the sides. Four buttons: +50, -50, +1000, -1000 with on/off. Size would have to be under 25mmx25mmx20mm including a small battery, with a parts cost under $20, ideally $10. Is something like this even remotely possible? If not, what would be a good way to do this at any size, assuming size is the problem. I'm looking to make four to ten units.[/quote]

Bigglez
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Re: Miniature Numeric Display - Is it possible?

Post by Bigglez » Sun Apr 06, 2008 8:41 am

Greetings (No First name Supplied),
uncalled1st wrote: I'm trying to find a way to make a small numeric display device with at least three digits, ideally five, to display numbers in increments of 50 (or 5 with a smaller display).
Similar to a pedometer?
uncalled1st wrote: Display would be on top, with tiny buttons on the sides. Four buttons: +50, -50, +1000, -1000 with on/off. Size would have to be under 25mmx25mmx20mm including a small battery, with a parts cost under $20, ideally $10.
Start with the LED display strip from 1970s vintage calculators,
still available from surplus electronics stores. LEDs are power
hungry, so you may want a "push to see" button with a timeout.

A better solution would be an LCD display (like a digital
watch or pager), I don't recall seeing three or five digits small
enough. A dot matrix LCD or the LCD screen for a cell
phone wold give you all the display ability desired.

Comments Welcome!

uncalled1st
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Post by uncalled1st » Sun Apr 06, 2008 11:43 am

Similar to a pedometer?
Not exactly. The idea is to record plane altitudes for a WW1 flying combat game. This would speed play and eliminate the need to record by hand. While there isn't much interest in games like this anymore, there are still several groups around that are still playing this one after 30 years or so.

I'll check the local salvage shop first.
Any idea how long an LED would run on a watch battery?

John

Bigglez
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Post by Bigglez » Sun Apr 06, 2008 12:15 pm

Greetings John,
uncalled1st wrote:
Similar to a pedometer?
Not exactly. The idea is to record plane altitudes for a WW1 flying combat game.
I mean to say "similar to a pedometer in size and display type"
uncalled1st wrote:I'll check the local salvage shop first.
Any idea how long an LED would run on a watch battery?
Not very long. IIRC, LED watches were rated for two cycles
per 24hr and one year battery life.

I was in Haltedon Friday and they still have boxes of NOS
calculator LED displays (the kind with the bubble lens).

If you always count in hundreds, skip the last two digits to
save even more hardware and power (i.e "35" = 3,500).

If you could use a single AA battery you could have much better
battery life. Shutting down the LED display (without loosing data)
would extend the battery.

Here's an LCD counter module that sells for about $35 in single
quantity. It would run "forever" on two AAA batteries, a little
less on a 3V coin cell. To implement your project would require
adding a uC (AVR or PIC), and of course a button or two.

Comments Welcome!

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philba
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Post by philba » Sun Apr 06, 2008 12:35 pm

If you increased your size requirements to 50x50, you would have a lot of choices. Note that driving a bare LCD is a bit tricky. not impossible but it's not as simple as turning on some segments like LED displays. Definitely takes a microcontroller.

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haklesup
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Post by haklesup » Tue Apr 08, 2008 11:36 am

Why do you need a display on the recorder? You could make a recording altimiter with mini USB interface with minimal parts count using SMT would only weigh a few grams without any case. You can use a handheld reader or PC to retrieve the data later.

I haven't looked for an off the shelf solution like this (altimiter only) but I have seen GPS recorders as small as USB sticks but they probably update too slow and are too inaccurate for your application but otherwise fit the bill.

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Post by Bigglez » Tue Apr 08, 2008 12:59 pm

Greetings Hackup,
haklesup wrote:You could make a recording altimiter(sic) with mini USB interface with minimal parts count using SMT would only weigh(sic) a few grams without any case. You can use a handheld reader or PC to retrieve the data later.

I haven't looked for an off the shelf solution like this (altimiter(sic) only) but I have seen GPS recorders as small as USB sticks but they probably update too slow and are too inaccurate for your application but otherwise fit the bill.
uncalled1st wrote:The idea is to record plane altitudes for a WW1 flying combat game.
I don't think they are actually flying... The altitude doesn't change during the game.

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Re: Miniature Numeric Display - Is it possible?

Post by k7elp60 » Tue Apr 08, 2008 7:53 pm

uncalled1st wrote:I'm trying to find a way to make a small numeric display device with at least three digits, ideally five, to display numbers in increments of 50 (or 5 with a smaller display). Display would be on top, with tiny buttons on the sides. Four buttons: +50, -50, +1000, -1000 with on/off. Size would have to be under 25mmx25mmx20mm including a small battery, with a parts cost under $20, ideally $10. Is something like this even remotely possible? If not, what would be a good way to do this at any size, assuming size is the problem. I'm looking to make four to ten units.
[/quote]
I think it is possible. Once you find some displays the rest should be easy.
With the size of surface mount parts it could be done with combination logic. I have made some name badges that are powered by CR2032 lithium coin cells.(20mm dia. X 3.2mm thick) They run LED's and the badge lights up for nearly a week continously. I don't have a picture of one, but I will attempt to take a picture of one that runs on the CR2032.
The attached picture is of one that runs on a CR2450 battery.(24mm dia X 5mm thick) Circuit actually has a voltage pump to boost the 3V to about six to run the blue LED's. Actual board size is 45mm X 75mm
Ned
Image

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haklesup
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Post by haklesup » Tue Apr 08, 2008 8:21 pm

I don't think they are actually flying... The altitude doesn't change during the game.
Then I fail to see why it needs to be as small as a postage stamp (roughly a cubic inch). I was picturing model airplanes. Most PC games would display altitude as part of the GUI making manual recording unnecessary

Aside the display a PIC or uController is a nice way to make this but since you can make an up down BCD counter with custom increments (including display decoding) using all combinational logic, you could also do it with a PAL.

Finally, keeping the cost for 10x prototypes under $20 each is going to be a challenge. Given budget = $200, use $100 to make ten 2-layer PC boards, recycle free batteries from trade show gifts and integrate battery holder into PCB for no additional cost.

Get 10 IC devices from Mouser or Digikey (what was the min order?) 10 is too many to sample, you could get 3 or 4 and each of your friends gets four then you have enough for free. Assume you can get the development software for free and borrow a device programmer (or have some willing friend do it for you). Assuming you choose a device that can drive your display and still have 4 or 6 I/O pins left over for your button inputs then all you need now is a $10 display.

Change to 4 units and the cost per unit goes up since the cost of project is unchanged. Change to a 4 layer PCB and now that cost $300 and the cost for 10 goes to $40. Find a way to do it without a PCB (handwired) and the major cost is just the display.

And that's optimistic.

Typical PCB prototype pricing (nothing tiny, no gold fingers)
http://www.pcbnet.com/a1ad22.asp

Go to the DIgiKey website, search on Displays, half way down the result page choose Display Modules LCD Character and Numeric. The resulting search tool has display size as a selectable filter. There seem to be at least 8 devices in the 30mm x20something mm outline and the good news is the most expensive one was less than $5.

This one http://search.digikey.com/scripts/DkSea ... 67-1792-ND looks good but since it is just a display you may need a second IC to serve as a display driver. Also you may want a 5 or 6 digit display in that case you will need to go wider than 30mm.

One last question, does this need to record ongoing changes or simply display the current count and forget when it is changed. You may just want to go with a homemade Abacus

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bbiandov
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Post by bbiandov » Sat May 17, 2008 12:23 pm

There are cheap 7 segment LED boards on eBay from some Chinese place. The board has 4 digits and you can dasiy-chain the boards for as long as 16 boards I think (that is 4*16 total lenght)

All drivers and memory is integrated, you just shift digits via TTL interface, SPI-like with clock and data. Very simple. I am thinking of getting few boards for a stock quote display at home so it always shows the going price - easy stuff via wget and yahoo quotes site.. the shifting will be bit bang via 2 pins on the parallel port (yes I am Linux). I even think Yahoo has a quote bash command that one can compile and run directly from a script.

Image

All and all they seem cheap at $5 bucks each, just that shipping is killing them. LOL

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Post by Bigglez » Sat May 17, 2008 12:42 pm

..

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