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I am trying to use an LED array to indicate a voltage level. For example, if the voltage is 3V, then 1 LED is lightened up. If 4V, 2 are lightened up. If 5V, 3 are lightened up, etc.. My previous design is to use many simple analog comparators to achieve this.

I now somewhat feel that it is possible to achieve the same effect with some Zener diodes. It would greatly simplify my circuit. How may I do it with Zener diodes?

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    \$\begingroup\$ If you're trying to produce a bar-graph style display, just use a LM3914. It's 10 comparators + divider chain + voltage reference in a single IC, and purpose-designed for making bar-graph displays. \$\endgroup\$ – Connor Wolf Mar 28 '15 at 18:51
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    \$\begingroup\$ What Connor said; this is a much easier approach \$\endgroup\$ – Eric Gunnerson Mar 29 '15 at 4:55
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Not trying to ruin the show, but the cheapest STM8 microcontroller would come for $0.5 and perform 10-bit A/D conversions for you. It will run without any external component and the programmer will come for another $3.5, which isn't bad at all.

Why not give it a shot??

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It's possible using zeners as voltage reference. You'll have to choose the zeners to each voltage level, taking on account the voltage through the led and resistor. The following example shows the functionality, but disregarding the values. You should do the math for the real case. (The intention of the 5V sourve is to simulate with a DC sweep, let's say from 0V to 10V and see the graphs showing the Vout varying).

schematic

simulate this circuit – Schematic created using CircuitLab

Again, to prevent "this-is-a-bad-idea-won't-work" kind of comments, disregard the values, this is just a functional example. Adapt to your real case, if need help, give more details on the components

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    \$\begingroup\$ This would have a better chance of being useful if you biased each of the zener diodes with a resistor so that they're seeing a few mA even with the LED off, but I'll give it a +1 anyhow. \$\endgroup\$ – Spehro Pefhany Oct 23 '14 at 10:03
  • \$\begingroup\$ @SpehroPefhany Many "tweaks" could be added. Your observation is valid, that's why I warned, this is just a really simple "proof of concept" it sure need to be adapted! \$\endgroup\$ – Sergio Oct 23 '14 at 10:21
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    \$\begingroup\$ -1 Even the general concept is totally flawed. The LEDs will come on with a very gradual intensity change. The thresholds will be lousey. So I say why bother even presenting a concept that is so far away from a decent design. \$\endgroup\$ – Michael Karas Oct 23 '14 at 14:16

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