Quad-7segment display (again)

[Armagon]

Deal all:

Some weeks ago, I built a Quad-7segment display, I used 4 digit (18mm), the pins are multiplexed, 8 pines for segments and 4 pines for common anodes, and it work excellent, but now I tried to build the same display with a big display 25mm and the intensity is very low, Could someone explain me how can increase the intensity?
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The Henry Ford specifications

 

[BenjaD]

That's because the leds are larger (or there are more of them) and so each segment is drawing more current. Hence, the intensity is lower as you multiplexing straigt from the PICAXE.

You can solve this by using a set of transitors to sink the current from a different supply to drive the leds.
http://194.201.138.187/epages/Store.storefront/?ObjectPath=/Shops/Store.TechSupplies/Products/ICO050

This means that the picaxe will tell the transistors to allow current from that second source to the leds. Allowing a fully bright led display.

Just don't forget to make a common ground or it won't work!

Hope it helps, Ben

 

[Dippy]

Just expanding on Benja who is quite right.
Larger displays tend to have more than on LED in series.
For example The Kingbright 1" display hs 2 LEDs per segment , therefore the Vf is greater.

So, your limiting resistors per segment need to be reduced or supply voltage increased. And, as suggested, it would be good idea to use a transistor switching thing.

You may have to do a calc with all those Vfs and Vce figures kicking about. For example the Kingbright I am looking at has a min Vf of 4.0V. Not much V left for you to fiddle with, so it may require a higher Vsupply. You may be able to use FETs and no limitng at 5V, you'de have to experiment.

As you don't mention the value of Vcc, and the pdf image is too poor for me to see the LED type, and i can't see what happens after J1, and my crystal ball has clouded, it is tricky to advise.