Insolation is measured in terms of radiant flux, measured in Watts.  This little gadget stores energy in a set of capacitors, so yes, Dr. Brown, there are flux and capacitors here.  But alas, very little time travel.


For the midterm project for Sustainable Energy, I made a rather crude, yet elegant (in a prototype sort of way) voltmeteter.  With a 12” square high-efficiency photovoltaic panel formerly of Cornell’s Hybrid Electric Vehicle project (material diverted from waste), some 1F ultracapacitors, and an NTE 1508 bar graph driver, it’s not a particularly complex circuit to make.


The NTE 1508 bar graph driver chip is nearly identical to the National Semiconductor LM3914.  The documentation for that chip is much better, so follow the wiring diagram for that chip (PDF).  Instructables’ LM3916 driven VU meter instruction set is also a good resource, the LM3916 being very similar to the LM3914 and LM3915.

The NTE 1508 + LED set draws a surprising amount of power.  The capacitor bank drains pretty fast when the PV is detached.  But it works quite well when in partial or direct sun.

The trim potentiometer on the wiring diagram above is really useful, allowing easy calibration to suit the light.  In the 3914/3915/3916 the voltage divider has fixed resistors, replacing those with a variable resistor is a much better arrangement, given the different use of the chip.

Helpful hints:

  1. the chip is ‘sinking’ power from the LEDs, which have their positive leg on the power rail (+3.3V +/-)
  2. the NTE 1508 works with either +5V or +20V supply voltage.
  3. use the potentiometer to trim the scale for full reading on the bar graph/LED set.  if you like, connect pin 9 (MODE) to pin 3 (V+) for bar mode, leave open for dot mode)

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