Scheme level indicator for a variable resistor on the “loose”

Somehow, in one homemade product, I wanted to introduce an indicator of the position of the twirl on LEDs, I saw this somewhere on the Internet, I really liked it. And this was the very moment when the LM3914 was not brought to the store around the corner.

Since the hands were already itching, it was impossible to retreat! The simplest solution to the problem would be to repeat the internal structure of the LM3914 and assemble a level indicator on a bunch of comparators. But it’s not interesting!

It would be enough to repeat the circuit on comparators with a voltage divider.  I didn't need any other features.
It would be enough to repeat the circuit on comparators with a voltage divider. I didn’t need any other features.

The outputs of the LM3914 have built-in current regulators. Accordingly, at the output of the comparators, it would also be necessary to add current-limiting resistors so as not to burn the LEDs and the outputs of the microcircuits. It was vital for me to have a scale of 14 divisions. Therefore, it would take 14 comparators, 14 LEDs, 14 current limiting resistors and 15 resistors for the reference voltage divider (something like this, maybe I didn’t take it into account). Already quite a few details are obtained against only two LM3914 microcircuits. And even if we take quad comparators, it still turns out 4 chips! And since such a booze according to preliminary calculations, a decent number of components is obtained, I decided to go in a not quite standard way.

In terms of the number of components, this circuit does not exceed the possible solution on comparators, the same 4 microcircuits and three dozen resistors. But the circuit turned out to be more interesting and I got more pleasure from the design process.

I will try to briefly describe the basic principle of the circuit. LED scale at the outputs of shift registers U2U3 under the influence of strobe pulses from the generator U1 sequentially filled with “units”, because the register data input is connected to the power positive. This continues until the voltage DAC summing DAC on resistors R18-R33 will not overvoltage Setting at the output of the variable resistor RV1. At this moment the signal Compare at the output of the comparator U4 resets the outputs of the shift register. After that, the circuit starts to work again. Due to the high speed of the circuit, an optical illusion is created that the LEDs glow continuously (stroboscopic effect). The operation of the circuit is illustrated by the graph in the figure below.

In a good way, the current-limiting resistors for LEDs should be linearly reduced as their position increases. But I didn’t do it. Due to which an interesting visual effect was obtained: the LEDs flare up smoothly as the resistor rotates. It turned out somehow very lamp on analog. As they say, this is not a bug, but a feature.

There is another way to equalize the brightness of the LEDs. A pause must be added at the end of each measurement cycle.

PS Don’t ask me why I do this. Everyone organizes their leisure time in their own way, someone plays chess, and someone is engaged in circuitry.

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