I am making a big led clock. I will post an image of the first digit below. It is common cathode. I was wondering if I would be able to use 4 74hc595 shift registers like in this video: DIY Digital Clock Homemade - YouTube
Just wondering if it would be possible and all that. Thanks!
Sure, why not?
Can you try to get the schematic. I saw just a glimpse of it in that video.
Since the display is composed of many individual leds, you are free to configure it as you please: common cathode, common anode, voltage (by combining groups of leds in series etc.)
High power shift registers eg tpic6b595 can sink current only, so need a common anode display.
Lower power 74hc595 devices are more versatile but I’d guess can’t fully drive such a display.
The download to the schematic is in the description. Also I think it would work because his display uses way more current than mine
Rapid80:
Just wondering if it would be possible and all that. Thanks!
Yes. You see that it's possible in the video.
I also told you in your cross-post that it's a bad video.
You are using the 74HC595 outside it's specs with that many LEDs in parallel and without CL resistor.
And this is the third recommendation you had about using the TPIC6B595.
How many more do you need.
Get a 12volt supply (or old 19volt laptop supply), and make strings of three (or five) LEDs with a CL resistor per string.
Can use multiple strings per segment.
Drive the (common anode!) segment strings with the TPIC6B595, one chip per digit.
That uses three Arduino pins for the whole display.
Wise to use a WeMos D1 mini or NodeMCU if you have internet near.
Then you can get accurate time (NTP) off the internet, like your PC/laptop/phone does.
No RTC module, no more adjusting (twice a year).
Leo..
I am trying to use a 5v supply for this. Also I wouldnt have the code or a schematic if I were to use the TPIC6B595. I would also have to change what I have so far to common anode. I think that I am absolutely clueless about this. I don't even no what "CL" means.
This is seriously beyond my knowledge at this point, and I don't know what to do anymore. I don't have code, I don't have drivers, and this is really running me down.
Rapid80:
I don't even no what "CL" means.
A LED needs a CL (current limiting) resistor, to keep the pin and the LED in the safe zone.
Rapid80:
I don't have code...
I assume you have an Arduino, and a RTC (real time clock) module.
Why not start with that.
You can display time on the serial monitor. No parts/soldering needed for that.
Many examples on the net and on this forum.
Use the search field on top of this page.
After having completed that successfully you can decide if you want to go for the MAX7912,
which is basically designed to drive eight small 7-segment displays matrixed,
with build-in current limiting, so no LED resistors.
Problem with that chip for large displays is that LED current (brightness) is divided over the eight digits.
And if you want multiple LEDs per segment, brightness is divided even more.
LEDs in parallel don't share current equally, so there could be darker/brighter LEDs in the segments.
Or the 74HC595.
~7-10mA pin limit and 70mA package limit, that should be set with seven resistors per chip.
Not matrixed (one chip per digit), so LED brightness could be a bit more.
But still uneven brightness if you parallel more LEDs.
Or the 74HC595 with an ULN2803 driver chip, to boost LED current.
This enables to use strings of LEDs, which means the same current through the whole string, which hopefully also means more even brightness.
Downside is that you must use a higher supply voltage, to overcome the Vf (forward voltage) of all the LEDs in the string.
But higher voltage could also mean lower current draw.
Downside is that you are looking at two supplies, or a buck converter for the Arduino/RTC.
A TPIC6B595 basically replaces the two chips above, and is more efficient (fets vs. darlingtons).
Both ULN and TPIC can only sink current, so common anode digits only.
Hope I didn't put you off too much.
Leo..
Thank you for your help. I got my rtc to print the time in the serial monitor last week, so thats good. And I can change what I have now to be common anode, but I still don't have code to run the whole thing, or even a schematic to start designing. Is there a way to do it with still only using 5v but using more arduino pins? Using only three would be nice, but there are more for a reason. I can't seem to find videos that show exactly what to do, because I use a lot of current. I will do as much as I can, but I am terrible at coding, and I wouldn't know where to start to make some sort of a schematic, but I really appreciate your reply.
Your comment clarifies a lot, so do you know where I could start with the TPIC, like any tutorials or a schematic or really anything that could keep me moving in the right direction? Thanks.
This clock is for my amazing teacher so I really want to get everything right and for it to still look good in the process. Also I have a cord (for lack of the correct word) that can supply 19.5v dc and 3.33a. My goal is to also really keep the cost down and hopefully supply it with 5 volts, but it doesn't seem like that is going to happen.
I have a little less than three months to do this too, so hopefully that is enough time. Also, i did some more research and it looks like transistors can be used to allow more current? Not sure exactly.
The schematic (and code) will be similar to any Arduino project which uses a ds3231 or similar RTC, and a 4 digit, seven segment common anode display controlled by 4 shift registers.
The only special feature is that you are building the segments yourself by combining leds instead of using a ready built module. These segments will have a higher than normal power requirement, hence the suggestion about the tpic6b595 (of which you will need 4).
Edit
Here is an example of the display part. display | tronixstuff.com Your circuit could be similar, however, this one uses common cathode displays and also normal shift registers. The current limiting resistors may also be different, depending on your choice of leds and how you combine them.
Here's an interesting project with two digits, with code.
Leo..
Not knowing exactly what kind of LEDs You want to use I give You some general, and old, data.
A red LED will drop the voltage by 2,5 volt. How many LEDs do You intend to use in each segment? Suppose connecting, in serial, 5 LEDS needs 5 * 2,5 volt = 12,5 volt plus some volt for the current limiting resistor. Say You need a 15 to 18 volt pwr supply.
Running the LEDs in parallell each LED needs a current limiting resistor. The disadvantage using parallell is that the current for each segment will increase. Say 5 LEDs needing 20 mA each. That makes 100 mA per segment and a total of 700 mA for each digit. 4 digits would then need 2.8 Amps.
Get a 5 volt pwr supply of some 5 Amps and You are cleared to go.
Here are are the Led's that I am using: Amazon.com
There are 3 different currents for the segments in a digit. Segment A has 6 leds. Segment B has 7 leds. C has 7. D 6, E 7, F 7, and G 4.
I really hate to say it but I think that i am in over my head on this one 
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I would love using 74HC595 shift registers, but apparently for my use, that's not possible. I'm going to take a little bit of time to just calm down and think.
Rapid80:
I would love using 74HC595 shift registers, but apparently for my use, that's not possible. I'm going to take a little bit of time to just calm down and think.
It looks like a 74HC595 could not fully drive (or sink) even one of those leds with a spec of 20mA at 2 volts. But even if you have already bought them, they are cheap enough to write off and 3 months is a long time to get replacements. Just don’t order stuff directly from China at the moment.
Yes, Railroader, those are the leds. I bought 2 of those, so 200 leds. Wow I just realized I spent around 100 dollars on this so far. Geez, I must have a really great teacher.
Why have You fallen in love with the 747HC595? You need to solve the current feeding of the LEDs. You have told You want only 5V pwr being used. Then You will end up in a forrest of power transistors.
Creat a plan for the entire project, not only for small parts of it.
Maybe a better, and easier solution is to send Your teacher a postcard every year. I did that once.