How to use LEDs in Place of 7 Segment Display

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narindia16

Joined: 04 Aug 2009
Posts: 16
Location: Ambala

04 Sep 2009 18:10 how do i make a huge 7 segment display

I Got a clock circuit. It is for 6 seven segment display. I want to make a big clock. Is it possible that after testing this small clock.....i replace the 7 segment display with Bigger board of LEDs, soldered in the shape of 7 segments. If yes what changes i have to do with in the circuits. I am attaching the circuit along with this Problem.

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pakitos

Joined: 14 Nov 2005
Posts: 470
Helped: 66

04 Sep 2009 19:05 how to make large 7 segment led display

Dear narindia16 why don't you use larger 7 segment displays? I think it will be more neat to use 7 segment displays.
check google to find the size that suits you.
If you still want to use leds give me the max size of the number that you want.

Check this a big led 7 segment
http://www.qrp.pops.net/cmos1.asp

Thank only by the Helped me button

pauloynski

Joined: 06 Oct 2004
Posts: 277
Helped: 34
Location: Brazil

04 Sep 2009 21:00 where would you use l.e.d.s

There are lots of very large 7 segments displays on the market. The only problem is that the big ones have 2 to 4 leds connected in series for each segment. This means you´ll need a higher voltage to drive them. If you´re constructing your own digits, a simple solution is to use 1 led per segment or to connect 2 or 3 leds per segment in parallel (one limiting resistor for each led).
Regards

sheth_ka

Joined: 29 Aug 2009
Posts: 23
Location: Philippines

05 Sep 2009 1:48 make a big 7 segment display

narindia16 wrote:

it is possible to make bigger 7 seg display using leds..i actually prefer to use a larger 7 seg display than to improvise using parallel leds..if your going to use a number of leds to create a larger digit this means it will consumed much current..however if your going to use bigger 7seg display this will require higher voltage..so its up to you if your going for leds or bigger 7seg..practically speaking bigger 7seg displays are much expensive compared to using leds..goodluck!

nandhu015

Joined: 11 Feb 2006
Posts: 641
Helped: 46
Location: Tamilnadu, India

05 Sep 2009 2:13 atmega 7 segment pnp

74hc244 is not capable of driving led's, use pnp transistor to drive the led's.

Nandhu

narindia16

Joined: 04 Aug 2009
Posts: 16
Location: Ambala

05 Sep 2009 3:40 driving 4 segment displays with a pic

Thanks a lot for your suggesstions........i think using a bigger Segment will be a better idea..... what changes i need to make in the circuit??? as you told that i will be requiring more voltage........

nandhu015

Joined: 11 Feb 2006
Posts: 641
Helped: 46
Location: Tamilnadu, India

05 Sep 2009 5:41 how to use the 7 segment display?

narindia16 wrote:

You can use pnp transistor for higher voltage driving

Nandhu

senthilkumar.b

Joined: 29 Aug 2009
Posts: 54
Location: india

05 Sep 2009 5:56 seven segment display with leds schematic

Hi this is senthil.

From your schematic, you are using common cathode display.

you can use any LED for display.

you should know the led operating voltage.

this operating voltage should given as driving voltage of below circuit.

How to use LEDs in Place of 7 Segment Display

How to use LEDs in Place of 7 Segment Display

you should provide seperate drivers for each LED.

can contact at rashdriver(at)in.com
Enjoy with your clock.

bye.

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

06 Sep 2009 20:10 7 segment display driver

It is not a good idea to connect load to NPN transistor as senthil showed. It will unnecessary dissipate power through 470Ω resistor which will increase the power-supply's current requirements. Also there is no limit on current that will flow through LED.
Use combination of NPN and PNP as shown. You need 7/8 such driver circuits for each segment. You need to change value of R1 (470E) depending on supply voltage V+ and segment's current requirements.
You can get rid of transistors connected to common-cathode (T3/T4) and connect it directly to UN2803 driver which is already used in your design.

Edit: Forgot to put base resistor for BC557. Corrected it.

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Last edited by CMOS on 08 Sep 2009 16:53; edited 1 time in total

rushi53

Joined: 19 Aug 2009
Posts: 36
Helped: 1
Location: India

07 Sep 2009 6:20 large 7 segment

u can construct a big 7 seg disp using LEDs,
connect them in the shape of 7 seg disp.
u don't need to change the programming.
just connect vcc of all leds in a segment together and take out single connection.
thus u will have 8 connection. This will be same as a normal 7 seg disp.

Let me know if you need any more help
__________________
Thanks,
Rushikesh
www.projectsof8051.com

senthilkumar.b

Joined: 29 Aug 2009
Posts: 54
Location: india

08 Sep 2009 7:20 7 segment led clock display

Hi,

Iam sorry for missing the current limiting resistor series wth the LED.

But mine is not going to consume more power.

just analyse the picture and conclude which one is better for your application.

Chip select is common for both. just iam consider about driver.

Signal power dissipation:915.2uw

Source power dissipation:375.7mw

Signal power dissipation:31.2uw

Source power dissipation:14.98mw

Kindly correct me if my thought is wrong.

Senthil

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

08 Sep 2009 13:31 7 segment display clock

BC557 is connected in wrong way in your simulation schematic.
Power dissipation in BC547 is high because I forgot to connect base resistor for BC557. Connect 4k7 resistor to base and see how it goes.
For better understanding you should also see voltage across transistors and LEDs to see if they are fully turned on.

This disadvantage of your circuit is that if you have more than 1 LED to drive, the base-emitter voltage (Vbe) required to turn-on the transistor will be much higher and if it exceeds 5V, microcontroller will not be able to turn it on. In my circuit, Vbe is fixed and you can drive any number of LEDs.

electronicslab

Joined: 06 Sep 2009
Posts: 31
Location: On Earth

08 Sep 2009 16:41 how to use the seven segment display

Sorry for this post.
One question.

If we avoid using transistor from the above circuit diagrams what will happen?
Why do we need transistor?

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

08 Sep 2009 16:48 7 segment display large

Microcontrollers are not capable of driving high voltage / high current loads. So to drive bigger loads you use transistor. You cannot get rid of it.

senthilkumar.b

Joined: 29 Aug 2009
Posts: 54
Location: india

09 Sep 2009 5:39 driving 7 segment displays

Hi,

I got your point.

If the driving current requirement is more then we are going to use darlington. Otherwise simple NPN/PNP low power transistor driver.

The revised diagrams are below.

But i think that FET is the proper choice for driving such a loads from microcontroller signal.

Your guidence are always welcome.

Bye.

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

09 Sep 2009 5:42 led on pnp transistor

You still forgot the base resistor for BC557. See my modified schematic above.

Yes MOSFETs are good for such applications.

senthilkumar.b

Joined: 29 Aug 2009
Posts: 54
Location: india

09 Sep 2009 6:37 atmega connect big led digits

Now its updated.

Yes now the power dissipation improved.
Fine.

Bye.

electronicslab

Joined: 06 Sep 2009
Posts: 31
Location: On Earth

09 Sep 2009 7:02 how to use seven segment

senthilkumar.b wrote:

Now its updated.

Yes now the power dissipation improved.
Fine.

Bye.

Hello,
What's the purpose of this circuit?
What are trying to do with this circuit?
How did you calculate the power level?(Watts)

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

10 Sep 2009 1:05 Re: How to use LEDs in Place of 7 Segment Display

The purpose is to drive high current loads. Large 7-segments displays require higher driving voltage and current so you need such driving circuit.

electronicslab

Joined: 06 Sep 2009
Posts: 31
Location: On Earth

10 Sep 2009 3:06 Re: How to use LEDs in Place of 7 Segment Display

CMOS wrote:

The purpose is to drive high current loads. Large 7-segments displays require higher driving voltage and current so you need such driving circuit.

In the circuit above is it 963.8uW at 2.5Vdc?

CMOS

Joined: 06 Jan 2004
Posts: 810
Helped: 39
Location: USA

10 Sep 2009 3:08 Re: How to use LEDs in Place of 7 Segment Display

That is the power that will be drawn from the microcontroller ! It should be actually measured at 5V.

kosta

Joined: 25 Jan 2002
Posts: 38

10 Sep 2009 6:29 Re: How to use LEDs in Place of 7 Segment Display

7 segment display 250mm (driver Allegro A6275, non-multiplex, VCC=12VDC) and 500mm (driver Allegro A6276, non-multiplex, VCC=15VDC)

http://www.elcom.rs/led_7seg.htm