4 x 7 segment displays

[SimonTHK]

Hello Electro Tech Online forum supporters

I want to have 4 x 7 segment displays in a project. Since I am using a quite big Uc I can easily get 11 output pins for this and might aswell do when I have the ports.

My idea:
First I have to pull these displays to ground (the 7 legs), I think thats called "common anode" displays. I should be able to do this by turning off my pins on my uc. I never did this, so can anyone confirm if that is a normal way to pull something to ground at an input pin on a uc=?

Also my displays need 10v but my uc can only give 5v. So if I add 10v one side and 5v (if the display is meant to be turned off) at the other side, will it blend? or will I have 5v running through the display and some current aswell? In theory it should, but I dunno if a uc can have current running through it backwards when used as an output?

7 of the pins works at output to the displays, so the displays all use the same 7 pins. I then want to turn on 1 display at a time using 4 outputs and 4 transistors.

Can anyone confirm my idea? Correct my mistakes.

 

[SimonTHK]

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[StudentSA]

Hey,

Please don't forget to put resistors on all the 7 lines of around 330 Ohms...

Cheers,
StudentSA

 

[JimB]

A multiplexed display is OK, but suffers from lack of brightness as each digit is only illuminated for a part of the time.

Consider an LED driver, I have used the M5450 quite successfully, and it just needs 2 or 3 pins on the microcontroller to drive it.
Look here:
https://www.electro-tech-online.com/custompdfs/2011/04/57504.pdf

JimB

 

[OlPhart]

I rcmd using a driver, either BCD-7 seg or a simple ULN2003 (or equ).
2 reasons: 1> most uC have a 10mA current limit on outputs, even those that are higher; think of the added power dissipation.
2> look at the uC max voltage on any I/O pin; usually same as Vcc or 1 diode drop above.
Unless a good reason not: a BCD-7 seg is way easier to code for, instead of having to make & use a lookup table.
Driving the anodes sequentially is std multiplexing, but there are drivers that do all that too. See Toshiba TB62709, but ST probably makes an equ. Good Hunting... <<<)))

 

[SimonTHK]

A multiplexed display is OK, but suffers from lack of brightness as each digit is only illuminated for a part of the time.

Consider an LED driver, I have used the M5450 quite successfully, and it just needs 2 or 3 pins on the microcontroller to drive it.
Look here:
https://www.electro-tech-online.com/custompdfs/2011/04/57504-1.pdf


JimB

the one you link till have outputs, and can only provide 15 ma per output. I need 25 ma which is what my psoc Uc can handle, not as output though.

I could look into a display driver, but it has to be a 25 ma and it has to be for common anode display´s

 

[SimonTHK]

let me turn around my quistion

Can anyone lead me to a bcd to 7 segment display driver for common anode displays with 25mA for each segment? I just cant seem to find that.

 

[SimonTHK]

This 74ls47 might be the one sink 24ma, but that must be enough!

The DM74LS47 accepts four lines of BCD (8421) input
data, generates their complements internally and decodes
the data with seven AND/OR gates having open-collector
outputs to drive indicator segments directly. Each segment
output is guaranteed to sink 24 mA in the ON (LOW) state
and withstand 15V in the OFF (HIGH) state with a maximum
leakage current of 250 mA. Auxiliary inputs provided
blanking, lamp test and cascadable zero-suppression functions.

 

[JimB]

the one you link till have outputs, and can only provide 15 ma per output. I need 25 ma which is what my psoc Uc can handle, not as output though.

What on earth is a psoc Uc ? and are these LED and why does it need 25mA?

I could look into a display driver, but it has to be a 25 ma and it has to be for common anode display´s

The M5450 is intended to drive common anode LEDs although it does not explicitly state that on the datasheet I linked to.
Why MUST you have 25mA drive to the LEDs?

JimB

 

[SimonTHK]

What on earth is a psoc Uc ? and are these LED and why does it need 25mA?



The M5450 is intended to drive common anode LEDs although it does not explicitly state that on the datasheet I linked to.
Why MUST you have 25mA drive to the LEDs?

JimB

I just checked the datasheet again, it says 20 ma not 25ma, my bad. https://www.electro-tech-online.com/custompdfs/2011/04/0900766b80b79ad1.pdf
But the M5450 datasheet says 15ma, that is probably enough, but still, shouldnt I be able to find one that can provide the 20ma? Or is 15ma just enough?
Thanks for the help

 

[SimonTHK]

psoc uc is a uc from cypress.
PSOC- Programable system on chip https://www.electro-tech-online.com/custompdfs/2011/04/PSOC.pdf

 

[SimonTHK]

Hello

I ended up buying this SB-Projects: saa1064

it seems very much what I want. I could have used the one you linked to before, but it used serial communication and I rather use i2c

Thanks for the help