Need a LED Display

Question

PROJECT:

I'm building a Digital Clock controlled by a Arduino micro-controller. I want it to display the hours, minutes and seconds on a LED Digit Display. Therefore, I need to have several digits, preferably 6 that are all linked together meaning as one piece and can be used on a breadboard.

QUESTIONS:

1.) Since there are several models and that I'm just a beginner (student) I need advice on what model I will need that I can put on a breadboard. I can find single digit displays at Radio Shack which i've already used in building a simple counter that goes from 0 to 9. However, I need a display with at least 6 digits. Therefore, what Model# would you suggest and where could I order this online.

2.) I have downloaded the specification sheet to the single digit display I'm using now (Model# ELS-321HDB). I find certain specification sheets hard to understand especially when it comes to the understanding the pin layout for all the anodes and cathodes. Any advice where I could find a educational source on how to read a specifications sheet for a digit display. Also is there any online resources out there that you would suggest I download specification sheets from. That is because some places request a certain fee while others are free.

Answer 1

6-digit 7-segment displays are not very common: Single, 2, 3 and 4 digit modules are much more easily sourced.

Here is one 6-digit 7-segment intelligent display module that can be bought as a kit or fully built - it actually consists of two 3-digit displays on a single PCB, with a serial interface:

It uses a serial input, 9600 baud, 8 data bits, 1 start bit, 1 stop bit and no parity.

Alternatively, consider using a 4-digit module with a colon indicator midway (e.g. from SparkFun) and tack on a smaller-sized 2-digit display module for the seconds.

Modules like the one above are more suitable for a clock than regular 7-segment displays anyway, with the hours and minutes separated by the colon.

Using a smaller seconds display module will increase readability of your clock as well.

Answer 2

Try to choose Common Anode type displays because with your microcontroller type it is easier to sink current than source it.

There are multiplexed displays available try to then those as you don't have to wire them yourself.

Usually the multiplexed displays are available in 4 digits. Here are a few of them available at Mouser:

http://www.mouser.com/ds/2/427/tdc10m-88849.pdf

http://www.mouser.com/ds/2/244/lite-On-LDC-M3904RI-187275.pdf

http://www.mouser.com/ds/2/427/tdc10m-88849.pdf

BTW, unless you want to learn, there are other simpler to wire clock projects available. I just found one today. It uses an AVR.

Answer 3

Typically you can get six individual digits and just put them next to each other. You can drive them each in turn by switching the common cathode of each in turn.

Does the display have to be 7 segments? A hd44160 based lcd character display (1x8, 1x16 or 2x16 typically) Is easier to drive on a breadboard.

Answer 4

A reputable supplier of components will often provide the datasheets for free on their website.

Reputable suppliers I like and most often use:

1. Digikey
2. Mouser
3. Newark (associated with Farnell and Element14)

There are a few others, too. Another good place to check for datasheets is on the manufacturer's websites. There are also datasheet catalogs which have links to many different datasheets, for example Datasheet Catalog. Personally I don't use these too much because the suppliers/manufacturer websites are often times much easier to parametrically search for the part I want.

As far as driving the LED displays go, the most efficient pin-wise is to use some sort of multiplexing scheme and rapidly flickering between digits that it appears like all digits are on at the same time. This question deals with a 4-digit 7-segment display which uses a multiplexing scheme.

Semi-shameless plug, I recently published a blog post on how to drive a simple 4-digit multiplexed 7-segment LED display.

Here's the schematic for the board (ignore the very ugly PNP transistor symbol, the library file I have is quite terrible):

Basically, I'm using a shift register designed for driving multiple LEDs since the micro-controller by itself can't reliably source/sink the necessary current required by all the LEDs. The shift registers control the sink (current flows into the sink), which determines which segments are on. The current is sourced through a PNP transistor. Each PNP transistor determines which digit is on at any given point and time, ideally only one is on at a time. The code I posted quickly cycles through each digit to give the illusion that they are all on at the same time.

To extend to more digits you just need to add more PNP transistor units.

Also, the part I was using had all 4 digits plus a little more integrated together, but you can just as easily get multiple single digit 7-segment (or 14-segment) LED displays and wire them up equivalently.

As a side note, I'm driving my circuit directly using a microcontroller without an Arduino (the one pictured is just doubling as my cheap power supply and programmer), but you can just as easily drive the circuitry using the Arduino platform.

Answer 5

Old question, I know, however think this might be a good and easy start. Take a look at the KEY&LED modules, very nice, integrates buttons, simple to use and only requires 3 wires. Can also used on a breadboard with some dupont wires if you want to. Wrote a library for it (fastest around) and also includes a clock example (example #2 of #5), a pretty good start to make your own clock. You can find it on github:

https://github.com/codebeat-nl/xtm1638

Here a photo of one of the cheapests modules around:

The controller TM1638 is very frequently used in set-top boxes, dvd-players and such. Take it apart before throwing away and reuse these front panels, it is pretty straight forward and educational too. You can also keep the plastics of the front panel and could be a good start for designing/completing a (custom) case.