2017-01-18 Simulating An Analog Meter

A detector or discriminator in an electronic device might need to be adjusted to a very few points on a scale of a hundred or more points.  A digital indicator typically indicates only a fraction of that, possibly 16 points.  This is why the analog meter is still useful: it can indicate a small change on a much larger scale.  I would like to make a device that is much cheaper than the analog meter, yet can indicate a small change in a much larger voltage or current.

I had a thought.  With today’s 3d technology and super strong magnets, it might be easy to do this.  Back in ‘the old days’ they used to make super sensitive meters by replacing the meter needle with a mirror.  Then a light went through a narrow slit and reflected off the mirror onto a somewhat distant surface, and movement that couldn’t be seen on the needle was easily seen on the light line on the surface. 

Another idea.  If the circuit is designed like a Wheatstone bridge, where the meter is showing only a small fraction of the total reading, then a 16 bar digital meter might be usable.  In other words, if the 16 bar meter shows 1/8 of the full scale reading, then it would be like looking at a part of the scale of a 128 bar meter.

But the problem is the measured quantity might suddenly change to a much different value which would no longer be in the small scale.  Therefore the small scale should be able to readjust itself to cover the new point.  There could be a ‘zero’ button to let the user recenter the 16 bar display on the changed value.

Some form of automatic feedback correction should be able to do this readjustment.  The adjustment could be done manually, but it seems that it can easily be done automatically.  The adjustment and settling times should be quick enough to not interfere with the user’s measurements.

One thing that occurred to me is that a good sensor of small level changes might be the ear. I could try connecting the voltage output to a voltage to frequency converter. The slight voltage changes would change the frequency and the ear could discriminate very small changes in the tone. A simple oscillator such as an astable multivibrator could be used.

Another idea. I’d like to investigate how sensitive the visual system is to flash rate. I found that the reason they use a starting pistol for races is that the mind processes sounds much faster than visual signals. That’s because there is much less brain used in processing sound, so there are less delays. But can a person do a visual comparison of the flash rates of a flashing LED? Or perhaps compare the flash rate of two LEDs?

Another possible solution, which seems to be very similar to the magic eye displays. The single LED would be mounted on a rotating disk. It could be mounted so the LED is seen on the edge of the disk. The disk spins and the led moves from Left to right. As the LED appears on the left, the circuit turns it on, and it remains on for the time determined by the voltage. Zero volts would have a very short time and the LED would turn off at the left side. Maximum voltage would turn off on the far right and other voltages would be in between. So the user would see something similar to a bar graph, with a varying length of light depending on the voltage. I realize that the mechanism might be complicated, but the rotating LED might be replaced with a stationary LED and a rotating mirror. Or the LED might be mounted on a lever that is driven by electromagnetics similar to a speaker’s voice coil. The whole idea here is to simplify and miniaturize the display.

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