Hi, I'm new to the forum and to cockpit building/electronics. I'm trying to make an MCP for the zibo 737. I'm planning to use a separate power source (+5v) for the 7-segment displays. I'm going with the 74HC4067 -> DM13A -> single digit displays route. The wiring details on the site are excellent but I'm no expert with electronics. I was wondering if it is possible to power the 74HC4067 (16ch multiplexer) , the DM13A (led driver) and the 7-segment displays (common anode) with the same +5v and ground. I know that the other connections going directly form the DM13A driver and the 74HC4067 multiplexer are just pulses indicating data. My powering idea is this:

USB -> Arduino -> Data -> Multiplex -> Driver -> 7-Segment

\--------------------------------/  \------------------------------------------/

        +5v from USB                         +5v from other souce

Is this possible? Thanks for your time and congrats on your efforts for making cockpit building easier!

Ps: how much amperage per 7-segment should I consider? 20mA per segment x 8?
Nov 13, 2019 in Wiring, Powering by

2 Answers

Please read this first, the ground is common for circuits, positive sources can be independent.


Milton Rodriguez.

Nov 14, 2019 by
Thanks Milton, missed that page. I got it working perfectly!

You can power any quantity of multiplexers from the Mega +5 V output. They consume almost zero power (few micro, not milli Amps).
So for DM13A, the chip itself consumes very low current, don't count it at all.

But, as it drives the LEDs connected to it (up to 16) and the current for each can be 5-40 mA (the current can be set by external variable resistor from 2 to 20 kOhm connected to DM13A pin, as shown).

So, if all 16 LEDs (segments) are ON the full current will be  80  to 650 mA. Most probably you will use no more that 5-15 mA (resistor = 5-10 kohm)  and full current will be about  100-150 mA.

(the one-segment current in 7-seg. indicators usually  quite   low   for good brightness, even 5 mA, but it depends on the module)

When you use many LEDs in your system I recommend  to take any old computer PSU (old AT-type is prefered as it has power switch, but ATX can be adapted too) as it has at least 30A 5V output.

And, of course, using the PSU you can power all system (displays, multiplexers, etc., not using the Mega +5V output.

Main thing - never forget the good common (one for all devices in your system) ground thick wire. http://simvim.com/tips_wiring.html

The power (different +5V sources can be used to power different devices and never have being connected together!)


Nov 14, 2019 by
Thanks Vlad, It works perfectly!  I have and old 486 PC with the AT PSU lying around, great tip.

Also excellent job with the interface, easy to use and understand!

One last question, what's ENA (#21) on the DM13A connection for 7-segemts?

ENA - is the typical assignment for "chip ENAble" signal.
When this pin is in low level the ship is working, else it's closes the outputs. It can be used for PWM control: