Aonomus over at Procrastinatus has a LM3915 Based Spectrum Analyzer project in development that has been described step by step. The schematic is almost done and will be released soon.
"I have schematics mostly drawn up for a LM3915 based spectrum analyzer using Fliege bandpass filters to give me bands at 60Hz, 150Hz, 400Hz, 1kHz, 2.5kHz, 6kHz, and 15kHz."
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What I’m more interested in is the little LCD he’s using… there’s no mention of how he’s driving that…
If it were a little CRT I could assume he’s using the SA he built to drive the deflection coils in much the same manner as these “homebrew oscilloscopes” we’ve seen… but, from this angle anyway, it looks to be a little LCD…
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One of the videos shows just the LM3915 being used as a level meter with no rectification, thus its a little jumpy. I included a picture-in-picture view of the scope just so people could see how the opamp chops off the inverted part of the signal.
The LM3915 has the ability to regulate how much current passes through each LED making it very easy to drive a LED bar display without needing 10 resistors, only one to drop the voltage (since the LM3915 has its own built-in current regulation, it dissipates heat, running at 20V, the LM3915 would dissipate too much heat).
Just to clarify, there is no LCD or CRT, the first video shows a PIP view of my scope. The only thing holding me back at the moment is finalizing the board design and etching some PCBs.