Review electronics circuits with 7 segment display+74hc595


I saw this module on the internet: 4 bit 7 segment display with two 74HC595

It is a 4 bit 7 segment display with two 74HC595.

I recovered from some PCBs some displays of this type, I also have a common cathode display and a common anode, I also bought some 74hc595. I want to make the PCBs, but first I want to ask your opinion, if the circuits are made correctly, because they are not so easy to make at home.

This is for the common cathode:

This is for the common anode:

Do you notice any problems?

That module on the internet does not have resistors, so it relies on the 74HC595 to limit the current and it does not have decoupling capacitors.
We prefer that you show the pictures here.
I think the schematics are okay. A single 100nF for both 74HC595 and a single 10µ (or more, 47µF ... 470µF) for the led display is probably enough. One or two more 100nF does not hurt.

The schematic can be made prettier if you move the top 74HC595 to the lower part.
You have to fix three NPN transistors (Emitter <-> Collector).

Do you have a sketch ?

If you click on all the examples and try them in the simulation, then you see a number of options:

On this

picture Q1 is correct but for me Q2, Q3 and Q4 is wrong oriented. Why not use MAX7219?

You're right, I'll correct.
I plan to use MAX7219 as well, but for 5x8 matrices, I will return with this circuit as well.

MAX7219 is for up to 8 digits but can be programmed for less (from 1 to 8), is cheap and the scheme is relatively simple. If you use 74HC595 more elements are needed and the program will be more complicated because you have to take care of the appropriate fast multiplexing of the digits. MAX7219 takes care of multiplexing and has overall brightness control. The choice is yours.

I can't say that I necessarily have a sketch, but I have the source for a project.
I managed to test one circuit on breadboard, but something quite complicated came out.
I wanted to build these circuits because I have the parts, and to have some kind of universal board for displays (cc or ca), even if I will not have identical displays I will use ordinary wires; then, by this method I will have fewer connections to uC.

I noticed the mistake at the transistors.

Okay, so you have some parts and you want to use them even if it's a harder way, a lot harder. At least do you have ULN2803? It can replace your pile of transistors and resistors.

There is no point in giving money for modules just because they look better; I do circuits as a hobby only, so I like to use the recovered parts.

Do you mean something like this ?

Does it also work for c.c. display?

ULN2803 is suitable only for LEDs with a common cathode, because it is 8 transistors with an open collector. For LEDs with a common anode is suitable something like TPIC6B595 - its with a built-in shift register and 74HC595 is not needed in this case.

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.