Many questions about 7 segment display modules

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Kaellis991
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Many questions about 7 segment display modules

#1 Post by Kaellis991 »

This is a two part post concerning the use of 7 segment displays...

For months now I have been trying to build a COM/NAV radio using 7 segment displays but it's been a challenge trying to understand some aspects of these display modules.

Part 1;
I have been trying out (3) brands of 7 segment display modules as well as (3) different arduinos (nano, micro, uno) along with different wiring connections (Dupont, JST, and direct soldering) and no matter what I do the lighting up of the displays is so frustratingly intermittent.
There doesn't seem to be any obvious rhyme nor reason for the inconsistencies. Just barely touching the displays will cause them to either go off if on or light up if not lit and that is intermittent to say the least.
Other variables also include using powered USB hubs in addition to directly connecting to USB ports (2.0 and 3.0) on two different computers. Also I have tried 22ga., 24ga. and 28ga. wiring.

The only connections I am making to the display boards, for now, are the 5v power and GNDs direct from the different arduinos (in addition to trying out a 5V power supply) which lights up all segments of the displays. Sometimes it works sometimes it doesn't.

I am not mounting the arduinos nor the displays but just setting them on my work bench and using a power and ground wire to connect the two.
Usually after a few minutes the displays will light up and if I don't breathe on them they seem to be stable...for a while.
Is the fragile nature of these display modules normal behavior or am I doing something wrong?
EDIT: Or is it a matter of display module quality?

Part 2;
The website page linked below does a pretty good job of explaining connections as such (albeit related to Mobiflight) but there is information there that brings up even more questions.
I have tried to contact the website owner to get info but no luck yet.

There are instructions that make no sense to me (as a newbie) and some images that I think are incorrect, but don't know for sure since I am so new to this stuff.
Any chance that someone here could elaborate on information provided on this website to help me understand some of the things on that page?
If so I can post the questions I have relative to the website info.

https://www.737diysim.com/copy-of-wirin ... -arduino-1


Kirk

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Keith Baxter
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Re: Many questions about 7 segment display modules

#2 Post by Keith Baxter »

Hi ,

Here we go again.
I have flogged this dead horse until it is mince meat.

MAX7219 need to have a 10uf cap to stop electrical/data interference.

Keith
AMD RYZEN 9 5950X CPU, Corsair H80I cooler, ASUS TUF GAMING B550-PLUS AMD Ryzen Mother Board,  32Gb ram Corsair Vengeance 3000Mh, MSI GTX960 4G graphics card 

Kaellis991
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Re: Many questions about 7 segment display modules

#3 Post by Kaellis991 »

Keith Baxter wrote: Thu Mar 16, 2023 3:15 pm Hi ,

Here we go again.
I have flogged this dead horse until it is mince meat.

MAX7219 need to have a 10uf cap to stop electrical/data interference.

Keith
Don't the boards that the displays are attached to have that cap as part of the circuitry?
All boards I have been trying have a C1 mounted to the board so that can't be the issue.
Last edited by Kaellis991 on Thu Mar 16, 2023 3:37 pm, edited 1 time in total.

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Keith Baxter
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Re: Many questions about 7 segment display modules

#4 Post by Keith Baxter »

Kaellis991 wrote: Thu Mar 16, 2023 3:31 pm
Keith Baxter wrote: Thu Mar 16, 2023 3:15 pm Hi ,

Here we go again.
I have flogged this dead horse until it is mince meat.

MAX7219 need to have a 10uf cap to stop electrical/data interference.

Keith
Don't the boards that the displays are attached to have that cap as part of the circuitry?
Hi,
Short answer is NO.

Read the wiki
MAX7219
This example will focus on the MAX7219 character boards, which are available on internet for reasonable prices. The MAX7219 character displays consist of a small board with eight 7-segment LED displays, controlled by the MAX7219 driver chip. The boards can be daisy chained up to 4 boards, depending on your power supply. It is recommended to place at least a 10μF capacitor on the power input of each board. You can use the display to create for example a radio. It can also display a alphabet characters, but since it is a 7-segment display, this is limited to A, b, C, c, d, E, F, H, h, L, l, O, o, P, and S. In the first example we will set the frequency of COM1 on the display.
Keith
AMD RYZEN 9 5950X CPU, Corsair H80I cooler, ASUS TUF GAMING B550-PLUS AMD Ryzen Mother Board,  32Gb ram Corsair Vengeance 3000Mh, MSI GTX960 4G graphics card 

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Keith Baxter
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Re: Many questions about 7 segment display modules

#5 Post by Keith Baxter »

Hi,

I will chat with Karl on the AM implementation of the radios and the different MAX7219 variants.

Keith
AMD RYZEN 9 5950X CPU, Corsair H80I cooler, ASUS TUF GAMING B550-PLUS AMD Ryzen Mother Board,  32Gb ram Corsair Vengeance 3000Mh, MSI GTX960 4G graphics card 

Kaellis991
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Re: Many questions about 7 segment display modules

#6 Post by Kaellis991 »

Keith,

I took two of the boards that are being inconsistent, and by using a breadboard I added a 10uf cap connecting the +5v and GND (with long lead to positive) and I get no significant change in the reliability.

My wires go from the +5v and Gnd on the arduino to separate breadboard rows, then from these rows I ran a wire to the +5v and GND pins respectively on the display board.
On the breadboard I connected the two separate rows with the 10uf cap (long leg to positive) thus connecting the pos and neg sides with the cap.

Assuming all my dupont pins are connecting properly I still get the same intermittent behavior....on for a while and then off...then on....ad nauseum.

EDIT; AM is not even in the loop yet.

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Keith Baxter
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Re: Many questions about 7 segment display modules

#7 Post by Keith Baxter »

Hi,

For the cap to work it needs to be as close to the MAX7219 chip as possible.
Connecting a cap and then running wires to the MAX7219 is not going to achieve anything.

@SimPassion has a image of where the cap should be connected i think.

Keith
AMD RYZEN 9 5950X CPU, Corsair H80I cooler, ASUS TUF GAMING B550-PLUS AMD Ryzen Mother Board,  32Gb ram Corsair Vengeance 3000Mh, MSI GTX960 4G graphics card 

Kaellis991
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Re: Many questions about 7 segment display modules

#8 Post by Kaellis991 »

How does one add a cap close to the MAX7219 on a pre-made board like this?
Is the C1 not already providing that function?
IMG_6615.JPG

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Keith Baxter
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Re: Many questions about 7 segment display modules

#9 Post by Keith Baxter »

Hi,

I do not know that board. Will look it yup.

C1 seems to be the 0.1µf cap C2 is the 10µf cap.

Needs to be like so.
ice_screenshot_20230316-191334.png
ice_screenshot_20230316-191334.png (16.96 KiB) Viewed 22242 times
Keith
AMD RYZEN 9 5950X CPU, Corsair H80I cooler, ASUS TUF GAMING B550-PLUS AMD Ryzen Mother Board,  32Gb ram Corsair Vengeance 3000Mh, MSI GTX960 4G graphics card 

Kaellis991
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Re: Many questions about 7 segment display modules

#10 Post by Kaellis991 »

The display module is one I found at https://www.propwashsim.com/
They just arrived a couple days ago.
The size of these are better for my setup than the ones I got from Proto Supplies.

Same place I got my Dual encoders.

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