Can someone tell me how to wire up a 7 segment LED display?

Question

This is the specific display: http://www.allelectronics.com/cgi-bin/item/SDA-801/345/0.8%22#34;_7-SEGMENT_LED_DISPLAY,_C.A._.html

I'm very new to electronics so I'm still learning. I bought these displays and the spec provided doesn't even tell me which pin is +5V and which is the ground!

Answer 1

You can connect the +5V to the common anodes, but you need resistors in the cathode paths to keep it from burning up.

For 20 mA through each segment, you need a 150 ohm resistor (can you figure out how I got that figure? If so, you're making progress) from each cathode to ground (seven total). That will light all of the segments up (an 8). You can put a switch in series with each resistor and turn them on and off to light the segments any way you want. A convenient way to do that is to use a DIP switch -- 7 or 8 switches in a package about the size of the display.

Another way to do this is to use old-style TTL part outputs, such as 74LS244, connected to the cathodes but without the resistors in series. If you ground an input on the LS244, it's corresponding output will draw enough current to light the segment but not enough to melt it. That's how digital circuits control LED displays. Some of the newer logic parts (S, AS, F, BCT, ABT, etc) will draw too much current and melt things, so make sure you use LS or ALS parts.

Answer 2

Firstly it is necessary to see whether these displays are ''common catode'' or ''common anode''. Well I have checked: they are common anode.

You will see that in te keft fgure there are marked pine 1, 16, etc.
The others must be derived from the right hand figure...

But you cannot connect the anode to +5 and one or more cathodes to ground. It is necessary a current limiting resistor.

I too have begun: my advice is that you boy some simple kit, you assemble it and stuty the circuit.

Good luck