Led Dispay with mutiple grounds?

[noah4546]

If you look at the image. When i want a certain digit I have to change the ground not the vcc. Why. And what is the type of technology called.

[free_electron]

common cathode display. nothing weird about that.

[noah4546]

common cathode display. nothing weird about that.

Well, how do I use it with an arduino to display time. (Not asking for code)

[Paul Moir]

Set it up to sink current into the Arduino rather than source current from it.  1s will shut it off and 0s will turn it on.
Hint:
10110111 xor 11111111 = 01001000

[noah4546]

what I meant was swapping through grounds

[Paul Moir]

You mean multiplexing?  I'm not following your terms.

If so:  hang series resistors off pins 1-7.  Supply current from two arduino output pins to 8 & 9.  Sink the current from the 1-7 resistors into 7 arduino output pins.
You can only turn on one digit at a time, so you switch between the two digits nice and fast so your eye doesn't see them blinking.

I'm assuming there's enough output pins on an arduino.  I've never used one so I don't really know.
 

[sleemanj]

If you look at the image. When i want a certain digit I have to change the ground not the vcc. Why. And what is the type of technology called.

The picture you included appears to be a common anode display if you intended that the red lines indicate positive voltage and the grey ones ground.  So if you found you have to do the opposite, you have a common cathode display. 

In terms of multi-digit 7-segment displays, the "common" refers to the "digit selection pin", you can see why that is if you think of it as only a 1 digit display, like this...


Which is the "common" pin in that picture, clearly it's pin 8, so if you have to put positive to 8 and negative to one of the others to light a segment, then it is common anode.  If you have to put negative to 8 and positive to one of the others to light a segment, then it is common cathode.

Either can be driven with a micro controller directly, with shift registers, with discrete logic, with 7-segment drivers.... many ways to skin a cat!

The MAX7129 is a popular way to drive common cathode 7-segment displays.

[noah4546]

If you look at the image. When i want a certain digit I have to change the ground not the vcc. Why. And what is the type of technology called.

The picture you included appears to be a common anode display if you intended that the red lines indicate positive voltage and the grey ones ground.  So if you found you have to do the opposite, you have a common cathode display. 

In terms of multi-digit 7-segment displays, the "common" refers to the "digit selection pin", you can see why that is if you think of it as only a 1 digit display, like this...


Which is the "common" pin in that picture, clearly it's pin 8, so if you have to put positive to 8 and negative to one of the others to light a segment, then it is common anode.  If you have to put negative to 8 and positive to one of the others to light a segment, then it is common cathode.

Either can be driven with a micro controller directly, with shift registers, with discrete logic, with 7-segment drivers.... many ways to skin a cat!

The MAX7129 is a popular way to drive common cathode 7-segment displays.

That makes sence.  Thanks for the help.

[denelec]

Multiplexing is used to minimize the number of pins needed to drive a multiple digit display.
The drawback is that only one digit is lighted at each time.
You must adjust the frequency of the scanning so every digit appear lighted without flicker.
Multiplexing also decrease the apparent brightness of the display.  You increase the led current in consequence.