Instructables

Emma: an 8-digit Alphanumeric LED Display powered by Electric Imp

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Picture of Emma: an 8-digit Alphanumeric LED Display powered by Electric Imp
Emma is a public-domain reference design for an imp-powered device from Electric Imp.

Never heard of Electric Imp? It's pretty neat. "The Imp" is a tiny wifi-connected microcontroller packed up in the same form factor as an SD card. It's really easy to build imp-powered things, and once it's built you can connect your device to any wifi network and interact with it from anywhere in the world. Check out the imp if you haven't before before digging deeper: http://electricimp.com/

Devices that are powered by or enabled to work with an Electric Imp are called "impees" (just like one who is employed is an employee).

Step 1: Emma Schematic Overview

Picture of Emma Schematic Overview
Since Emma is a public domain reference design, anyone can take the schematics, gerber files, or bill of materials (BOM) and use them to order everything needed to build more Emmas. This is the case no matter how many Emmas you might want to make. Want to build a whole production run and sell them? Totally fine. Want to make some changes to they layout or tweak the design to add your own feature or twist? By all means, please do. 

The pdf of the Emma design is attached to this step in addition to the screen shots shown. The full project source for this design is available from the Electric Imp Dev Center. Note that many other reference designs are also available at on the Reference Designs Page.

Emma's design consists of four functional blocks: the power supply, the imp slot and ID chip, the LED driver and digit circuit (which is repeated 9 times in the design), and a digital ambient light sensor which was added just for some extra flair. The light sensor can be excluded without any ill effect (except, of course, that you won't be able to view the light level from anywhere in the world).

Emma's power supply uses the Texas Instruments AP1117E33G LDO to obtain a 3.3V supply from the board's 5V supply voltage - the imp, as well as the driver ICs for each digit, require a 3.3V supply. This LDO is inexpensive and easy to solder, and is a new addition in revision two of this design.

Note the Atmel ATSHA204-TSU-T part at U2, in the "Imp Slot and ID Chip" section. This part is an ID chip which provides the impee with a unique ID number. This number is used when the imp comes online and registers with the Electric Imp cloud; this is how the Imp Cloud knows what firmware to provide to the imp when it comes online. This part can be purchased and installed right off-the-shelf; no special initialization or configuration is needed. Just solder it down and you're good to go.

The Taos 856-TSL2561FN is a simple I2C sensor which can be used to detect the ambient light level around the impee. As shown on the schematic, this part has I2C slave address 0x29. Source code to read the sensor is included in this tutorial.

Next we'll take a quick look at the circuit which controls each display digit.

 
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tombrew (author) 1 year ago
I've just posted revision 2 of the Emma schematic and layout - this substitutes an inexpensive fixed-voltage LDO for the hard-to-solder Torex step-down 3.3V regulator, reduces the gap between digits, and improves board routing overall. Enjoy!
dlemke1 year ago
I would like to use this format to makea scoreboard for a racetrack, which would have 8-10, two digit numbers on a pole type arrangement. Is this possible with this instructable? The numbers would have to be bigger, as in 6-8", stacked on top of each other, mounted to a pole, so that everyone could see what racer is in what position, so it would have to be at least three sided, possibly 4.

Thanks for the great info and getting my intererest into possibly building one or two for a lot less than it would be to just buy them. These would be used at a racing kart track, possibly hooked into the scoring system, so it would be automated with the way the transponders would have them and would let everyone know what position their favorite driver was in or before the race, it could tell the drivers where they are to line up for the start.

If this is possible, maybe we could hook up by e-mail to get more info.

danl@mvn.net
tombrew (author)  dlemke1 year ago
Sure, that's totally possible. Your design would really be a new design, but the basic premise is the same.

The digits, because they're all serial-in, serial-out, are all daisy-chained together. You can daisy-chain more, but be sure your power supply is ready to deliver the necessary current. With every segment turned on, the design posted here draws about 2.67 Amps. An "average" draw is closer to 1 Amp. You'll need to make sure you understand how much current it will take to run the larger digits you want to use and then spec out your power supply accordingly.

The nice thing about using an imp to drive your data to the scoreboard is that you won't have to run any data lines out to it as long as you've got a wifi network up and running there.
elabz1 year ago
I thought it is impossible these days to hear about a new development platform given that the word get out through blogs, forums and various electronics magazines (which I read all - N&V, Servo, Cir.Cellar) . But I have genuinely never heard A WORD about Electric Imp until today, and it seems such an interesting idea. I definitely have to check it out.

And love your 15-segments, they are pretty much my favorite type of alphanumeric displays. Such a retro feel!
tombrew (author)  elabz1 year ago
Pleased to meet you as well :) We're glad you enjoyed it. You can pick up the imp and a breakout board on Sparkfun if you want to get started. We have a lot of quick examples to get you going at devwiki.electricimp.com. Stay tuned here as well; we'll be adding more instructables and projects soon.
have you tried reading from RSS feeds with this? twitter perhaps?
tombrew (author)  amandaghassaei1 year ago
Yes and yes, it's very easy to do via the Electric Imp planner. You'll need a little bit of code running on a server somewhere to handle your twitter API and form an HTTP post. Use the HTTP IN node in the Electric Imp planner to receive that HTTP post, with the "value" parameter set to whatever string you'd like to print, and the planner and default firmware I posted will take care of the rest. You can use this technique with just about anything: RSS, Twitter, a website or mobile app, etc.
sealman1 year ago
I have been unable to find the emma board can you help with this?
Thank you so much for you time and great job on this instructable!!
tombrew (author)  sealman1 year ago
Glad you enjoyed it! The Emma schematics, Altium project, gerber files, and firmware are all here: http://devwiki.electricimp.com/doku.php?id=emma

Note: We're spinning a second version of this board right now, with an easier-to-solder power supply and tighter digit spacing. Stay tuned!