Request for help on an LED bar graph circuit by an electronics noob.

[kchriste]

I know what an LED is, and I had a vague understanding of what a diode was; like I kept asking, is it like a check valve?

Yes, you are correct. Current will only flow one way through a diode.

I have no problems putting together a chaser kit, it's the modification for my needs I don't know much about

Your problem with modifying a typical chaser circuit using an IC like the 4017 will be the limited current capability of the 4017s outputs. The 4017 can only drive one (Maybe 2 if you push it a little out of spec) LED at a time. Your diode idea would require the last output to have to drive all 10 LEDs at once resulting in a very dim display because the 4017 will not be able to source that much current.

 

[ThrowingChicken]

Yeah I was afraid of that.

What if I went with a chaser circuit that uses larger, more powerful LEDs, but then replaced them with smaller ones?

 

[kchriste]

You could do something like that. Maybe choose one designed to drive light bulbs like one you posted at the beginning of this thread. Maybe post the schematic that goes with the PCB also.
But, it will take quite a few diodes and will have a very repetitive and predictable "un VU meter" type flash pattern. You'll also have to add a resistor for each LED to limit it's current.

 

[ThrowingChicken]

It's fine if it's predictable, the stacking motion is good enough for my needs.

 

[kchriste]

I think I found the schematic for the board you posted:
**broken link removed**
It looks like the circuit will already do exactly what you want anyway. You can just replace the bulbs with a resistor/LED or eliminate the transistors entirely and drive the LEDs directly from the IC's via 1K resistors. You could also "chop" the circuit in half if you don't want as many LEDs...

 

[ThrowingChicken]

Chopping it in half would just require me to hook up the 555 timer and just one of the 4015's, and the stuff in between, right?

 

[kchriste]

Pretty much. Pin 11 of the remaining 4015 (U1B) would be unused just like the 2nd 4015s (U2B) was. Pin 2 of the remaining 4015 would connect to the reset line just like the 2nd 4015s was. You would not need the 4017 (U4) either. This would give you a 6 LED display...

 

[audioguru]

A chaser circuit lights only one LED at a time.
A bar-graph lights multiple LEDs in sequence.
Their circuits are completely different.

 

[ThrowingChicken]

Yes, I know, that's why I was theorizing about using diodes, which I've been informed won't work because the power outputted at each individual light won't be enough to fully illuminate the whole strand. It was like a cheating way to get around it.

 

[Sceadwian]

Why not just use a micro controller and be done with it? If you need more output pins just use a serial shift register with an input latch. It's a WHOLE lot simpler, and can be expanded as easily as adding more shift registers, output drive can be increased by tacking adding a transistor to each register output.

 

[kchriste]

A chaser circuit lights only one LED at a time.
A bar-graph lights multiple LEDs in sequence.
Their circuits are completely different.

Yes... Usually they are. But the layout that ThrowingChicken posted and the matching schematic that I posted uses shift registers so he will get the bar-graph effect with no additional diode mods etc....

Why not just use a micro controller and be done with it? If you need more output pins just use a serial shift register with an input latch. It's a WHOLE lot simpler, and can be expanded as easily as adding more shift registers, output drive can be increased by tacking adding a transistor to each register output.

Why would the OP need a micro controller? As I stated to AudioGuru above, the circuit posted at the beginning of the thread actually does exactly what the OP wants (except that it uses light bulbs and not LEDs). It is made up of shift registers with the serial data input tied high and the clock tied to a 555 so the parallel outputs all turn in sequence. I'll admit that I didn't look too closely at the original PCB layout either until yesterday where I noticed that the 4015s were shift registers.

 

[ThrowingChicken]

Why not just use a micro controller and be done with it? If you need more output pins just use a serial shift register with an input latch. It's a WHOLE lot simpler, and can be expanded as easily as adding more shift registers, output drive can be increased by tacking adding a transistor to each register output.

I just don't know how. I mean, like I said, I can follow the directions for putting together the hardware, but it seems like I'd have to learn a lot to not only know how to plan the circuit but program the controller? You guys are experts, you know what your doing so to you it seems like the most logical step, but is it still so simple if you are brand new to it all?

Just to test out the VU meter, I ordered a small kit for a couple of bucks. I'll see if that gets me anywhere.

The static lights look like all they need is a resistor before them in the circuit, and I've looked into blinking LEDs and most of them say you don't need resistors at all.

If the VU meter works out then I think the only issue I will get caught up on is how to run the power to the individual components and have them all use the same power source and on/off switch.

 

[ThrowingChicken]

Yes... Usually they are. But the layout that ThrowingChicken posted and the matching schematic that I posted uses shift registers so he will get the bar-graph effect with no additional diode mods etc....

That schematic is actually a different lighting area of the same prop, and has been created to be film accurate. I also believe it was created by the help of a forum just like this one. The part I am working on is fuzzy on the details, meaning there is no real set way for it to work. The way a VU meter would work seems more accurate and might be a viable option.

 

[ThrowingChicken]

This is the basic idea of how the lights and switches would be wired. The main toggle switch cuts off power to everything, but even with it on, two of the LEDs don't light up unless the push button is pressed down.

**broken link removed**

 

[gramo]

Perhaps PIC micro's would be worth looking into? This is a very simply project to take on, and a good one at that to be your first.. If you have a couple of bucks, maybe grab a Intro to PIC micro's book, but as good as it is to have a solid understanding with assembly (the lowest form of programming with 35 instruction set), It’s really not required.

There are Free development tools for Higher level languages such as Basic and C. They are becoming more efficient and powerful as time goes by, and it allows you to 'take for granted' the complexity of assembler, especially with 32 bit math functions and array handling.

Using PIC micros lets you develop a circuit in a sense, but with a program. A single chip that can do thousands of things, their great tools.

An example of a program for your situation would be (Written in Proton+);

Device 16F876			' Define what device your using

XTAL = 4			  	' Set the Osc speed

All_Digital = True	  	' Make all outputs digital (turn of anolouge features)

Dim Pin as Byte			' Create a registry that can hold a value between 0 to 255

TRISB = %00000000		' Make every Pin of port B an output (theres 8 pins on port B 
	  		          '  the % modifer means I'm working in binary for the following number)						
PORTB = %00000000		' Set all the Pins to Low ( 0V)

Main: 					' A label

	Repeat				  

		  Toggle PORTB.Pin
		  
		  Delayms 1000
		  
		  Inc Pin
		  
	
	Until Pin = 8
	
	
	Repeat

		  Toggle PORTB.Pin
		  
		  Delayms 1000		  
		  
		  Dec Pin
	
	Until Pin = 255			  ' Pin will decrement to 0, then roll over to 255
	
	
	Goto Main 				  ' Do this for ever

Of course you dont have to go down that road, just thinking out aloud. You could use a flip flop type counting device and a few other things to do the same thing..

 

[ThrowingChicken]

Okay, well let's say that my interest in electronics does not surpass what I've asked about in this thread. What chip would I need to make the **broken link removed** What computer hardware would I need? Never mind the programing (for now), what would I have to do, assuming I had this chip programed and ready to go, to finish up the working circuit?

 

[Sceadwian]

Just a chip and a parallel port programmer, which can be made simply with a few passivate components, maybe a transistor. There are exaustive amount of information on Micro controllers out there. Just do a google search for PIC and light chaser, or PIC demo's. Check out Nigel's site. Don't be intimated by your lack of knowledge, just start reading and asking question on the appropriate forums. No matter how 'greek' the code or terms may seem to you at first it's really not that complicate. It's just another set of words to remember.

 

[xxxxxxxxxxxxxx]

How about a shift register??? That'd work, would it not?

 

[audioguru]

A chaser usually uses an oscillator and a CD4017 IC which turns on one output at a time in a sequence of 10, and repeats the sequence over and over. The circuit does not use diodes, the IC switches on and off the power to the LEDs.

A bar graph uses a completely different IC. The bar graph IC can be switched or wired to make a bar of light or a moving dot of light.