Need help building 6 digit 7-segment display

Using Arduino LEDs and Multiplexing
1

Hello everyone!

First let me tell you that I`m pretty new to Arduino, but I do electronics repair mostly on notebooks and TVs. My friend asked me to help him build a 6 digit 7-segment display. A big stopwatch essencially like this one: 6 Digit LED Digital Challenge Countdown Timer 10s Challenge Game Timer (youtube.com)

My question is more hardware\electronics related.

Anyway, I would like to ask some help to putting together this clock.

I`m want to use 4 inch displays, with high brigthness. So far I found two possible candidate:

FYS-40011DUHR-11

SA40-10 SRWA

After doing some research, I think the best way to drive 6 of these displays is by multiplexing with the help of six 74HC595.

However Im not sure if the drivers can actually take the amount of current these superbright LEDs need.

Also, I would like to use a DC power source for the clock, like a universal DC PSU with the proper power rating.

What do you guys recommend? Do you have any advice or tip on how to solve this?

Any input is welcome and thanks in advance!

2

The 74hc595 will not handle the voltage or current for those displays. You need something like an MIC5891 for the anode driver

and a TPIC6A596 for the cathode driver.

Apply to the segments and digits as needed by the display.

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3

I see! Thank you for your input.

Currently playing with easyEDA's schematic designer.
I will try to make a schematic with your component recommendations.

Will post it when I'm done with it.

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4

Sparkfun has some huge displays: I think they're 6" that come with SPI drivers so they can be daisy chained.

5

And the worst way for brightness, which is then divided over the number of digits.

Large common anode digits and TPIC shift registers is the preferred way.
As @cedarlakeinstruments said, go to Sparkfun.com and search for large display drivers.
Leo..

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6

Thank you for your suggestion. Getting the drivers from this site would be very nice, but sadly I'm located in Europe so it's not really an option for me.

Is the TPIC6A596 for anode and MIC5891 for cathode driver is suitible for these displays right?

7

There are a lot of Sparkfun distributors in Europe.

Forget about common cathode displays an forget about matrixing.
Just use one TPIC chip per digit, and daisy-chain.
Use a 100n decoupling cap on each TPIC, and a current limiting resistor for each segment.
Or use the Sparkfun breakout boards, which have these parts already fitted.

The TPIC6B595 is the go-to chip for this, if you want to make your own.
Or the TPIC6C596 if you want an smd footprint.
Leo..

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8

If you use the decimal point the current limit resistor should be twice what the segment ones are for the displays you listed. They have 2 LEDs in series for the DP and 4 for the segments, so the DP will have half the voltage drop of the segments.

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9

So I started playing with EasyEDA to make a schematic for the circuit. This is pretty much my first time so I probably making a lot of mistakes. :sweat_smile:

I tried to make it readable and I would like to ask for some guidenance on how and what to change on it.

This is how far I got:

Schematic_Ora3_2024-02-21
Schematic_Ora3_2024-02-211860×1241 168 KB

I forgot to ad that only 2nd and 4th displays decimal point will be used. So I not connected the others to the circuit.

10

I think you have to use a resistor for each segment to limit the current.

I would probably use something with an integrated current sink. (e.g. LED1642GW)

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Schematic_Ora3_2024-02-21
Schematic_Ora3_2024-02-211860×1242 181 KB

Thanks for pointing out, I forgot the resistors on the segments. What value should I use on the segment's current limiting resistors?

I would rather stick to Wawas recommendation with the TPICB595. Checking on the LED1642GW site I noticed its can only output 40mA max. Which I dont think is enough for my display choice.

12

What current do you need?
What forward voltage do the segments have?

You should get rid of the resistors on the common anode pins. now you have them for each segment.

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13

Omit the anode resistors - you do the current limiting on the segments. The value for the segments would be (12V - LED segment V)/segment current. For example the SA40-10 SRWA

(12-10)/.02 = 100 ohms for segments and (12-5)/.02 = 350 for the DP

This assumes a max segment LED voltage of 10V and DP voltage of 5V , for the typical values (8 and 4).

(12-8)/.02 = 200 ohms and (12-4)/.02 = 400 ohms.

I would use 150 for the segments - that would give 20 to 26 ma for segment current.

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Schematic_Ora3_2024-02-21
Schematic_Ora3_2024-02-211860×1241 193 KB

150Ohm for segments and DP too? Or 150 for the segments and 350 for the DP?

15

Each module mounts behind a large digit, with only a few wires going to the next digit.

They use 15 ohm resistors for their double 6-LED segments.
Leo..

16

350-400 for the DP

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17

Resistor value depends on the display you use. You linked to digits with strings of four LEDs in post#1. LED Vf also depends on the colour of the LEDs. There is a typical Vf table in the datasheet on that page. If you know total Vf and project supply voltage, then you should be able to calculate resistor value yourself.
Leo..

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Schematic_Ora4_2024-02-22
Schematic_Ora4_2024-02-221860×1242 200 KB

Dear everyone, I updated the schematic with your very helpful inputs. :pray:

I also changed the 12V DC input to a barrel jack, which is also connected to the VIN pin of the Arduino. Hope it`s the correct way to do it.
I planning to use a 12V\3A DC power adapter as the power source.

Can you please take a final look on it, if there is anything else I should add or change to it?

20

Did you forget to connect pin8.
Leo..

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