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I first want to say that this project is for a charity auction that happens a couple times a year and we would like to remove all paper from this process since the paper requires 7 people to handle and deal with and is way to frantic!

There are around 100 electronic displays we need to make for our next auction. We want it to be as low cost as possible. Right now we have settled on a 4-digit 7-segment LED display with an ATTiny chip. This gives us 4 digits and since the auction is by whole dollar amounts we won't reach anything above $9999 though above $999 will happen. This just straight cost (no enclosures, solder, boards and such) puts us around $4. Adding a battery case or even a wireless chip drives the cost up a bunch.

So my question is, what tricks can we do to drive the cost of this project down? So far the best we have come up with is to chain multiple displays together and drive it off one wireless chip. Any other tricks anyone can think of?

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The trick to low cost is getting the volume up. At only 100 pieces you're not going to get really low prices. $4 seems pretty reasonable, but don't forget the cost of building and testing. How will this system log who the current bidder is? Seems like that's missing from the electronic display. In the end, maybe paper is still the cheapest solution. – Olin Lathrop May 24 '12 at 17:21
Yeah, the 100 is a hard cutoff on volume pricing I have found. Building and testing will be done by volunteers. Logging who the current bidder is, is not a problem since it is silent and we have two projectors showing high bid and current bid number but good point. – Josh May 24 '12 at 17:24
A somewhat fuller description of the intended use would make the requirement clearer (to me at least). – Russell McMahon May 24 '12 at 17:59
You can probably find a calculator or similar that can have a processor added to control it - giving you display, case, battery holder, switches etc. – Russell McMahon May 24 '12 at 18:00
@RussellMcMahon The intended use is to show the current high bid of the item it is attached to so that we don't have to collect 100 clipboards and enter them in a small time window. Users will go to a bid station to enter their bid. Think electronic price tag but for an auction. – Josh May 24 '12 at 18:04
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3 Answers

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Since it is an auction, I assume the displays will stay in one place more or less. Try to get rid of the wireless chip, use plain wires for communication (I2C or SPI) instead. You may even do the power distribution over the wires to get rid of the batteries. Some tricks with decoration let you hide the wires easily if aesthetics are of your concern too.

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I think we are going to prototype this. Just working out how to reduce the cost now of the display, one avr and maybe a shift register if the avr we buy doesn't have enough pins to run a 4 digit 7-segment LED. – Josh May 26 '12 at 14:33
@Josh If any of the anwsers was helpful, please vote them up. If one reply is the best answer, please accept it as "best answer" ... there is a button for that. – suha May 26 '12 at 15:01
I know there is, but my reputation on this stach exchange isn't high enough to vote up. I also want to look at I2C and SPI a little bit more to see if it will work and do what we need it to. – Josh May 26 '12 at 18:38
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How about flash cards? or a big Calculator with BIG LCD numbers for the silent auction types. Hey that's wireless too. Type in the price and hold it up.. As along as you specify size, or distance of viewing. It can be obtained. $2 / 1000 pcs for A size. calc.

Specs please for viewing distance?

enter image description here

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You won't "hold it up" there are 100 items on tables and it is a silent auction which means people are bidding on it through out the evening. – Josh May 25 '12 at 17:57
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What you mean there are a hundred people with a hundred items and thousands of bids... crazy.. Put it on a website and big projector screen. for all to see like EBAY and tell everyone to borrow an iPod , cell phone or laptop to submit registered bids. like everyone else on EBAY. Then its just a web browser app. If you like my idea , dont vote just get cue cards... and some cute auctioneers. no just kidding then close this as answered and re-phrase the question for the programmers.. at http://superuser.com/

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That would be awesmoe and great, but I think you have deviated from the original question. Also, 1. not everyone will have internet access or a smartphone at this auction, 2, running a web server cost US money on top of the FEE to get the internet access into the venue that the auction is hosted at which sometimes in and of itself is $800 for ONE NIGHT. Also, I am a programmer, and that would be more for stackoverflow.com not superuser.com – Josh May 26 '12 at 14:32

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