Good idea, armorris. We could use devices using far less current and much lower voltage. Your comments inspire me to suggest that we could use an FPGA which could draw a couple of nanoamps in sleep mode while providing all the op amps we need and all the peripheral eeprom or SD card data storage we might require when active. We could store a graph of data over a long time period using very little power.
The author did a nice machining job on the mechanical parts, and the documentation was good, but as 78RPM pointed out, the circuit relies too heavily on the positive and the negative voltages being exactly the same. As 78RPM mentioned, a "rail splitter" circuit would solve that problem. Then, you could just run the circuit on one 9 volt battery. A rail splitter would consist of a second opamp and two identical-value resistors. The output of that additional opamp would be a virtual ground. Even if the two resistors (say 10K) are not identical, their ratio would not change and the error could be reliably nulled out.
You could make those resistors 100K and use an MCP607 ultra-low current dual opamp, which draws less than 25uA per opamp, and make a 9 volt battery last a really long time.
This is a fascinating project that could be a good science fair experiment measuring the effect on cloud temperature between summer and winter of carbon emissions using long-term readings. One could hook the output to an Arduino or Raspberry Pi and keep a log of readings on an SD card. One could also calibrate an analog panel meter using a custom decal (e.g., DecalPRO) with direct voltage or intensity units.
One problem with using two batteries for positive and negative supplies is that they get imbalanced over time. A better solution would be to use a rail splitter buffer opamp to create a virtual ground exactly half way between positive and negative points. TI offers a variety of these. The outputs of this, +,-, and VGND provides the supply voltages to your circuit.
The first Tacoma Narrows Bridge was a Washington State suspension bridge that opened in 1940 and spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed into Puget Sound on November 7, just four months after it opened.
Noting that we now live in an era of “confusion and ill-conceived stuff,” Ammunition design studio founder Robert Brunner, speaking at Gigaom Roadmap, said that by adding connectivity to everything and its mother, we aren't necessarily doing ourselves any favors, with many ‘things’ just fine in their unconnected state.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.