# Transistor timed LED switches

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#### HeatherM

##### New Member
I am trying to build a simple delayed turn on for a sequence of leds.
The schematic I am including is just the first stage but I already have questions.
The object is to turn on a series of leds each one after the first with a short delay between each. The delay goal is around 0.1 to 1second (I will determine proper delay experimentally).

So far I've only used transistors as amps in the linear range or as a switch, but not as any type of delay. The circuit I build i was experimenting with as shown to delay the turn on. The turn on speed was not great but it doesn't have to be. I would like it to be quick enough turn on so that you can't see the led turn on slowly.

What should I do to get a delayed turn on that I'm looking for? Oh and while I say this It might be suggested that I use a 555 or something, but I plan to have many of these delay things so 555s would just be too much.

ty

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#### MikeMl

##### Well-Known Member
How many LEDs?
How long is each LED on?
How often do you step to a new LED?
Do you want it free run (recycle, restart) or run through the sequence just once each time a button is pushed?

#### HeatherM

##### New Member
How many LEDs?
How long is each LED on?
How often do you step to a new LED?
Do you want it free run (recycle, restart) or run through the sequence just once each time a button is pushed?

Each Led will turn on and stay on with the half second or so delay between each. Will probably use 5 LEDs. I was going to add a 6th stage that instead of turning on a LED, it would reset the sequence (free run while switched on).

As far as the microprocessor goes, I did consider, but I only know C++ and C# languages at close to amateur level. So didn't want to play with that idea yet.

#### MikeMl

##### Well-Known Member
Use a 4017 CMOS decoded decade counter. Hook up outputs 1,3,5,7,&, 9 to 5ea. LED/resistors. A single clock oscillator (555?) to advance the counter. This will naturally give equal on and off times as it steps between LEDs. It will recycle automatically. If you're using high-current LEDs, you will have to add a Hex Buffer or five transistors...

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• LEDsequencer.png
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#### 3v0

##### Coop Build Coordinator
Forum Supporter
Doing it with or without a micro controller is OK. A C program and a \$3 18 pin PIC would make this very easy. It also allows you to change how the lights work easier then hardware based methods. You will need some way to program the PIC but that does not have to be expensive. (Thinking LVP)

This is an EXCELLENT first PIC project. A PIC18F88 or PIC18F1320 using internal OSC, 5 resistors, and 5 LEDs would be about it. And there a number of us here who would be glad to lend a hand.

3v0

Code:
...
void main(void)
{
char  x;
x=1;
while (1) // repeat forever
{
if (x & 0x20)  // when bit 6 is 1 start over
x=1;
PORTA=x;    // latch pattern to LEDs
x = x<<1;      // shift 1 bit left
// delay here ...
}
}

#### superfrog

##### New Member
Surely that would be better done in timer interupt than with active wait, wouldn't it

I do understand, though, your desire to keep it simple in this case.

#### 3v0

##### Coop Build Coordinator
Forum Supporter
Surely that would be better done in timer interupt than with active wait, wouldn't it

I do understand, though, your desire to keep it simple in this case.

If the processor is only blinking the lights a simple delay loop has no disadvantage.

3v0

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#### mneary

##### New Member
Oh and while I say this It might be suggested that I use a 555 or something, but I plan to have many of these delay things so 555s would just be too much.

ty
With 555's retailing at 20 cents in small quantities, what is "too much"?

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