hello,

I want to construct a 24 seconds shot clock for used in a basketball game. I plan to display the output in an array/segments of LEDs. Any help from you guys? Is there any IC that can drive 10 or more LEDs at the same time for each ouput pin?

 

I'm not sure what you want to do exactly, but LEDs can be connected in series if they are all required to be turned on and off at the same time.

Len

 

It's fairly common to use discrete transistors for driving those sorts of things, that way you can have whatever drive capabilies you want. Depending on the supply voltage you use, you can feed them all in series with a single current limiting resisitor. If your supply isn't high enough to do that, you can split them into sections - say 5 in series, with their own resistor, with the other 5 in parallel, with their own resistor.

 

Thanks Len, Nigel,

Please advice what transistor should I use. (My friend told me to use ULN2803A IC, but I'm still studying)

And about the shotclock, any help/similar schematic that i can possibly use as reference. (i figure out I'll use a count down timer).

 

Two 4029 presettable counters and two 4511 as BCD to 7segment decoder work fine. The ULN can also work as driver for many LEDs.

 

hello Sebi,

I'll try to use 4029 and 4511. I have just downloaded their datasheets.

Thanks.

 

It all depends on how much current you need, as it needs to be pretty bright the ULN2803A might not be big enough - something like a TIP31 or TIP41 will handle a lot more current.

 

Hi Nigel,

Suppose I'll use TIP31 or TIP41 transistors, and use a 12Vdc supply, the output is used to drive 20 LEDs connected in parallel each has 330 ohms resistor in series, can I directly connect the input (Base-Emitter) to PIC16F84A microcontroller? Please help me with the transistor's biasing resistors and their connections.

Thank You very much.

 

It's a big waste to have all the LED's in parallel with their own limiting resistors - it's far better to have them in series/parallel. So for your 20 LED's, you could have 4 blocks (of five LED's in series - with a limiting resistor) in parallel. 12V is plenty to feed 5 LED's in series - you would need to calculate the series resistor to give the correct current.

You can't feed a transistor directly from a PIC, you need a current limiting resistor - 220 or 270 ohm shoud do.

 

Anyone who wants to help me with my project. i need to construct a 24 second shot clock but i can't find what instruments to use. can you please help me.. i need the details.. thanks!

 

TIP31 and 41 ?? Have someone here ever heard about power MOSFETS ???

And if you know a little about programming, i suggest a PIC µC.

(My two cents !!)