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Electronics Gadget Design - Flash Examples Included & Pic(s)

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Banned
Basically the design is this. A strip of 20 or so led's (or any other light source which is extremely small that can create a nice fluent lighted bar look) that lights up accordingly to the voltage being delivered. See examples below for reference..

Lighted Bar Example - In Flash 6.0

Light Strip Picture

The source (direct current) would be variable from approximately 1-4 volts (this still has to be confirmed). Can anyone help me out on how to start a design like this? I can't seem to find a good light source (keep in mind it has to be as small as possible). But otherwise, if anyone has suggestions as far as the circuitry design or anything else i'd HIGHLY appreciate it. I think i at least deserve an award for illustrating the idea so well!! Haha. Thanks guys - i'm looking forward to hearing your ideas and input!

Thanks!

- RJ
 
you aren't supposed to bump more than once every 4 hours... in HT you dont really need to bump more than once per day or less.

anyway, a simple way to do it would be to put an increasing number of diodes in series with each LED. that way, as you go up, more voltage is required to reach turn-on voltage. make sure that you also have a resistor in series with each LED to avoid burning anything up.

unfortunately, for this method, you probably wouldn't be able to get more than 4 or 5 states between 0 and 4 volts unless you find some low-voltage diodes and LEDs. you might be able to use transistors but I haven't thought that through.
 
Sorry bout the extra bump. I'm just used to having the posts fall deep into no-where land after about 20 minutes in most forums.
 
I was going to suggest a bar-graph driver IC, but making the lower LEDs fade out is a bit tricky.

Actually, having just said that, if you use the IC in 'single spot' mode instead of 'bar' then interconnect the LED outputs with silicon diodes in the appropriate orientation (so that when LED 3 is on, some power is able to leak throught 2, and a little less through 1).

If that doesn't work, then I think you're going to be best off using a microcontroller.
 
Ok, here's the dealio on your design:

You want to feed that analog voltage source into an N-bit A/D converter. The output of that is BCD format, which gets fed into a BCD-to-decimal decoder. The output of that decoder has 2^N lines - only one of them will produce a '0' (ground) corresponding to the BCD code input. That will in turn ground the correct LED on the bar (hook up the LEDs through resistors to a voltage source) and thus lights up. The only problem with this is that it only lights up one LED at a time.

If you want to light up the current LED and everything below it, then you will need to use something called a priority decoder/encoder in place of that BCD-to-decimal decoder.

This design may use up a lot of discrete components, but it is straightforward.

Another design would involve the use of an A/D converter and a programmable logic array. The PLA takes care of all the digital logic described above, but requires the logic to be worked out on paper. Using this approach, you can customize how you want the led bar to light up. It also requires you to program the PLA.

These are the two approaches I can think up right now.. I'm sure there are more ways to do this design, but I hope this gives you some ideas.
 
Here's another design that's easier to implement:

Get a resistor ladder, for example, 10 1kohms resistor in series and at each point of the ladder, hook it up to a comparator. Have a reference voltage of Vmax (in this case, its 4V) at the top of the ladder. The other input to the comparator is your Vin (which moves from 0-4V). The output of the comparator is either 5V, or 0V. This can directly drive your LEDs. Using this approach, the highest level led and everything below it will light up.

Or you can use an ic called an LM3914 and cascade two of those to get a 20 LED driver. 3 would get you 30 leds, etc etc. I think this would be the simplest approach as it is even more straightfoward than the two approaches I mentioned yesterday night and requires minimal components.
 
The LM3914 or LM3916 would be the easiest way to build the circuit. The limitation is that there are only two modes of display. The chip is designed to drive the LED's in dot or bar mode.
Dot means that only one LED is on at a time though it does smooth the transitions.
Bar means that the highest LED and all below it are on at time.

If that is acceptable then look at the pdf application and tell us if you have any more questions.
LM3916
I haven't looked through all of the bar graph drivers to see what the differences are.

If you really want the display to look like the one in your flash. (nice job btw) I can think of two possibilities.
1) Impose an AC voltage on your input. A sawtooth would approximate your display I believe. You would have to take the AC into account for your display but that would be easy to do when you calibrate it.
2) Add a diode and resistor combination to each of the driver outputs. Use the driver in 'dot' mode. Orientate the diodes so that only the LEDs below the one that is on can sink current. Pick the resistors to get the fade of the LEDs that you showed in your flash. OK, this is a quick idea, but I think it would work. Thinking about it you may not even need resistors, the voltage drop of the diodes would fade the diodes below it. On the other hand each diode would drop 0.7 volts so it may not work. This idea needs more thinking than I can give it tonight.
 
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