connecting a 4 digit 7 segment display to NP2

I have just bought this 4 digit 7 segment display unit: http://www.communica...ils/P3579877383

Suddenly I feel real stumped as to how to connect this...and couldn't really find a datasheet where I was told to look.

It's connection are marked as SDO, VCC, GND, SDI, LCK, and CLK.

As they mention on their page "only need 3 wires to MCU" of which I know two will be VCC and GND but the data connection is what is puzzling me.

Voltage I see is 5V but am now wondering if the NP2's 5V out would be enough or if I would need an external 5V

EDIT: or are they excluding the VCC and GND in their count and referring to SDI and SDO and CLK instead?

Furthermore I am suddenly worrying about code to send data to it and wonder if something like the code from http://blog.mark-ste...hift-registers/ or https://stefan.co/el...h-bitshift-ics/ will work at all

From what I could see so far I need to connect from the NP2 as follows:

MOSI (pin 11) to SDI on the display

SPCK (pin 13) to CLK on the device

Now I can only assume that an IO pin on the NP2 needs to go to LCK on the display?

Your thoughts on this?

The ground has always to be wired: that should be the very first connection you do!

However, the ad is pretty "optimistic": three-wires means just the logic signals, so excluding any supply and ground.

Your guess about the connection is correct: just add the ground and the +5V supply. It is up to you decide whether using the Netduino power source or an external. Assuming that the circuit were well-designed (just a guess), each 74HC595 SHOULD NOT drain more than 70mA, thus four displays would be less than 300mA. That's not a problem for the Netduino board, neither in case of USB power source.

My personal suggestion...

Use an external +5V supply (1A is far enough) with an Amperometer in series, then use this supply for JUST the display board (leave the Netduino powered in another way). Write your own app, then light up all the 32 segments, then take a look at the total current.

This will tell you whether the circuit has been well-designed (i.e. the 74HC595 are stressed or not).

Good luck!