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Topic: [SOLVED] 6 pcs of 4 inch 7-segment LED + UNO (Read 3294 times) previous topic - next topic

Bronson_alex

Nov 03, 2017, 02:21 am Last Edit: Nov 04, 2017, 04:37 am by Bronson_alex
Hi,

I am planning to connect 6 pcs of 4 inch 7-segment LED to my UNO.
What is the best way to do it? Which IC should I use to drive my LEDs?

Bronson

Wawa

4" 7-segment displays have several LEDs in series per segment. Usually four.
Vf (working voltage) of four LEDs can be 8volt or more, depending on LED colour.
Easy to drive them with a TPIC shift register.
TPIC6B595 (ebay) if you build it yourself.
Sparkfun uses the TPIC6C596 on these boards.
Leo..

Bronson_alex

4" 7-segment displays have several LEDs in series per segment. Usually four.
Vf (working voltage) of four LEDs can be 8volt or more, depending on LED colour.
Easy to drive them with a TPIC shift register.
TPIC6B595 (ebay) if you build it yourself.
Sparkfun uses the TPIC6C596 on these boards.
Leo..
Thx Leo.
That is what I am using right now. The TPIC6C596 from sparkfun. But I keep damaging the DP (decimal point).
Could it be because of the sparkfun board is designed for their own 6.5" display https://www.sparkfun.com/products/8530 ?
Or maybe my 4" displays are bad quality? I have damaged 4 DPs  :smiley-confuse:
Should I use bigger resistors (such as 220 ohm) between my 4" and TPIC6C596 board?

Bronson

Wawa

The DP most likely has one LED, while the segments have four.
The current limiting resistor has to be calculated for that.

Post a link to the display,
and post supply voltage and segment resistor values you're now using if you want help with that.
Leo..

Bronson_alex

The DP most likely has one LED, while the segments have four.
The current limiting resistor has to be calculated for that.

Post a link to the display,
and post supply voltage and segment resistor values you're now using if you want help with that.
Leo..
Can't thank you enough for that, Leo.


Each segment resistor value = 220 ohm + original 15 ohm resistors from Sparkfun board.
Supply voltage to Sparkfun board = 12V (from VIN of UNO), so 12V to segment.
Only chain 2 pcs of 7-segment LED to UNO at this moment. The finish product will be 6 pcs.

Without 220 ohm resistors, DP segments are broken.
With 220 ohm resistors, no damage but after 2 hours of operation, the resistor of DP segment became very hot.

Here I attach the spec sheet of segment display.

Bronson




Wawa

#5
Nov 03, 2017, 08:04 am Last Edit: Nov 03, 2017, 08:10 am by Wawa
The third jpg shows five LEDs in series for the segments, and one for the digital point.
I'm going to assume you use the RED displays, where the LEDs have a Vf of 2 to 2.4volt and a max current of 20mA.

You can safely drop the 220ohm segment resistors to 100ohm if you want more brightness.
That will give (12volt supply - 5*~2.2volt LED) / (100ohm + 15ohm) =  ~9mA LED current.

The DP will have the same brightness with a (12volt - 2.2volt LED) / ~0.009A = ~1088ohm = 1k resistor.
Leo..

Bronson_alex

The third jpg shows five LEDs in series for the segments, and one for the digital point.
I'm going to assume you use the RED displays, where the LEDs have a Vf of 2 to 2.4volt and a max current of 20mA.

You can safely drop the 220ohm segment resistors to 100ohm if you want more brightness.
That will give (12volt supply - 5*~2.2volt LED) / (100ohm + 15ohm) =  ~9mA LED current.

The DP will have the same brightness with a (12volt - 2.2volt LED) / ~0.009A = ~1088ohm = 1k resistor.
Leo..

Thank you so much, Leo.
Will do as you said, I will post the result by tomorrow.

Bronson

Bronson_alex

#7
Nov 04, 2017, 04:21 am Last Edit: Nov 04, 2017, 04:28 am by Bronson_alex
Leo,

It has been tested for 2 hours. Looks good! The brightness is good and no components is hot.  :)

Btw, I use 220 + 15 ohm for segment and 1k + 15 ohm for DP, as:
SEGMENT : (12V - (5*2V))/(220 + 15) = ~9mA
DP: (12V - 2V)/0.009 = 1111 ohm = 1k ohm

Here I attach the photo. I cover it with dark glass as they are too bright for my eyes.

I hope there is no problem when I chain all six 7-segments LEDs. Does it mean I have to use at least 2A adaptor just for six pcs of 7-segments LEDs? 36 x 9mA x 6 pcs = 1.9A ?

I owe you one, Leo. ;D

Bronson
http://www.pt-altraman.com/

Wawa

Nice big displays.
Good to see you have it sorted.
Karma for posting back.
Leo..

Bronson_alex

Nice big displays.
Good to see you have it sorted.
Karma for posting back.
Leo..
Does it mean I have to use at least 2A adaptor just for six pcs of 7-segments LEDs? 36 x 9mA x 6 pcs = 1.9A ?

Cheers

Wawa

A string of five LEDs in a segment uses 9mA (not 9mA per LED).

Eight segments (7 + DP) * 6 = (8 * 9mA) * 6 = 432mA (0.432Amp)

A 12volt/1Amp supply is more than enough for six displays and the Arduino, even if you decide to use 100ohm resistors for the segments (higher brightness).
Leo..

Bronson_alex

A string of five LEDs in a segment uses 9mA (not 9mA per LED).

Eight segments (7 + DP) * 6 = (8 * 9mA) * 6 = 432mA (0.432Amp)

A 12volt/1Amp supply is more than enough for six displays and the Arduino, even if you decide to use 100ohm resistors for the segments (higher brightness).
Leo..
Thanks!!!


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