• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help needed to make a driver circuit for three large seven segment displays

Pavi98

New Member
Hello all,

I am trying to build a custom, large scale, three seven segment displays which should has a LED (maybe two LEDs) for each of the segments and intended to drive through Arduino. How should I build a driver circuit for this three seven segment displays and do you have a circuit diagram for this? As I am a newbie in electronics, I'm quite not sure how to build a driver circuit for the display.

Thank you very much.
 
Last edited:

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
I use a shift register 74HC595 and a ULN2002A.. The reason is each digit is permanent ( not multiplexed ) and the ULN2002A can take LARGE displays

1618578900315.png
This allows many displays to be cascaded... 74hc595 hard to get now....
 
Last edited:

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
Sorry... I use farnell, Rapid or RS... I don't have an account with digikey.. When I looked you could get a tube of 25 , I only need 4 at a time..

So for those unfortunate to not have full access SOIC or a tube..

I did notice you can get singles from digikey over half are obsolete so limited choice..
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
How much current per segment?

The ULN2003 has a max current per segment and a max current per package. There is an 8 channel version of that chip if you wanted to handle a decimal point.

You can complicate matters, by adding a latch, so you can pre-load everything and then display.

Your code might have to handle leading zero suppression.
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
The ULN2003 has a max current per segment and a max current per package. There is an 8 channel version of that chip if you wanted to handle a decimal point.
One in that series hasn't a TTL input... +7v can't remember which one.. Scratch that.. its the ULN2004..
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
This https://www.mitsubishielectric-mesh.com/products/pdf/m63836kp_e.pdf

and the ULN2803 are 500 mA, 8 channel units. https://www.ti.com/product/ULN2803A

The are really nice chips. They were just confusing when I first used one. There is a pin that returns all of the spike suppressors to the + supply and the appreciated part is that with the inputs floating, the output is off.

ASIDE: Off the beaten path:
i worked in research and Radio Shack was a place I used of a few parts here and there. I had problems "buying" because of "petty cash
" restrictions. Only the business office had purchasing cards. At one time, you could spend up to $50.00 cash and get re-imbursed.
The mechanical supply places have excellent shipping times. e.g. mscdirect, mcmastercar and grainger have excellent shipping times. My favorite is mcmaster. mscdirect's prices has gone up significantly, but postage is another matter.
Generally one postage charge unless an item has to be drop shipped. Items usually arrive the next day.
If I'm willing to wait up to a week, I can pick up locally with no postage. At the local office, there is very little stock. They stock items for users.

At one point, most of my electronics ordering was from Newark.com. Catalog and call for every price. No web at this point. I had an account representative.

One boss generally allowed me free reign and I was able to help other employees as long as the time wasn't excessive. The other boss was a nanosecond time manager.
 
Last edited:

AnalogKid

Well-Known Member
Most Helpful Member
I'm quite not sure how to build a driver circuit for the display.
Without more information, neither are we.

What voltage(s) are available to power the display?

What voltage is available to power the electronics?

What is the desired current through each 2-LED string?

Is the Arduino driving each segment individually (21 output lines), multiplexing the digits (10 output lines), or some form of serial interface (shift registers, I2C, SPI, etc.) (3-4 output lines)?

ak
 

Pavi98

New Member
I use a shift register 74HC595 and a ULN2002A.. The reason is each digit is permanent ( not multiplexed ) and the ULN2002A can take LARGE displays

View attachment 130941
This allows many displays to be cascaded... 74hc595 hard to get now....
Hello Ian,
Thank you very much for the reply.
What is mentioned as "A, B, C" in each of the shift register ICs and can I use 500mA from each of the outputs of ULN2002A for driving LEDs?

Thank You.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
The datasheet says yes. It also says you can parallel the drivers.

Drivers made for LED's might actually be better because it's generally easier to control brightness and you get current control.
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
What is mentioned as "A, B, C" in each of the shift register ICs and can I use 500mA from each of the outputs of ULN2002A for driving LEDs?

Thank You.
These are just connected together to allow data throughput.. A goes to A etc...
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
Can I use ULN2003A instead of ULN2002A?
You must... My first schematic was wrong.. 2002 do not work as intended... BUT!! as Mike pointed out.. ULN2803 is even better..
 

Pommie

Well-Known Member
Most Helpful Member
Personally, I'd get four of the 32x8 displays See here. You'll get a 64x16 display that's ~256mm x 64mm and easily driven with spi. No driver circuit required.

Mike.
 

Latest threads

EE World Online Articles

Loading
Top