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Posts: 127
Hi Guys

Just wanted to double check... I have a load of 7 segments added on the pedestal now for the radios but some are lacking power and I want to add some LEDs to brighten the backlights a little. Can I use the old PSU I have...

My plan is to run 5v and Gnd to the 7 segments and LEDs and take a GND from the PSU and plug it into an available GND on all Mega cards so its common throughout? Is that the correct way?
2020-04-07 22:31
From: ETSI, Germany
Posts: 4465

Stephan is the Master of Power and electronics :thumbup: :thumbup: :thumbup:
But i think the required power of 7 seg is not the problem.... In case of Multiplexing whorst case there are just 8 Segment LD active same time..... With 7 tubes the highest point is 7*8=56 Segments of realy low current Segment LED.

I not know how many power the chip need for itself.... But i would think 7 Displays NOT reach the Limit of the Board. ( Maby Stephan knows it better)

About your Main Questions

1. Please confirm you remove the Diode OR you wire 5V to each of your 7 Boards directy.... If you buid a chain then Displays of Board 3 and behind are have not enough power. But that not means your suply is to low.... This is jut in case of Chain the Displays.
Use Forum search if needed. There all is explaned multiple times.

2. If you realy like to use the Power suply... Maby Stephan will confirm that.... I would Set 5v and GRD of that Suply to the Displays Input Pins.... And finaly GRD from Suply also one time to the Arduino Mega where the Display is connected thorugh CS/DIN CLK Pins.
If your Megas are still combined via a GRD Loop then you must connect your Power suply just to a GRD Pin at ONE of your Megas Via the existing loop the suply is then connected to ALL Megas same time.
Good Luck !
2020-04-07 22:50
Posts: 127
Thanks Pizman

I didn't bypass the diods on them. I have them (4x) plugged into the mega at the moment, some are a little bit dimmer but readable. I tend to pick one GND pin on the board and connect them all to this 1 wire with 4 tails :) and the same with the power, perhaps this is my problem :D
2020-04-07 23:20
From: EDDG, Germany
Posts: 1687
I don't see any problems there. I connected a total of 14 7-segment displays with 5 digits each to a Mega without a separate power supply and there are no differences in brightness. The digits are not all controlled at the same time, but are multiplexed. In this respect, only one digit is active per MAX board, you just don't see it because each chip is multiplexed at 1 kHz.
An external power supply is normally not required.
Within a chip, the 7-segment digits should not be of different brightness if the 2 x 4 tubes are involved.
2020-04-08 19:16