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    carlb got a reaction from Fmilburn in Circuit Help   
    There's a decoupling cap after the input jack (to block DC), then the common type of precision rectifier (made using opamps and diodes), which then uses the capacitor to store the peak voltage, which the LM3915 displays. That was a classic circuit in the electronics hobbyist mags 30 to 40 years ago (along with the classic 741 opamps of the time). You'll find plenty of other precision rectifier and peak detector circuits (with varying hold times which you can easily tweak) on the web, old books, and even in the LM3915 datasheet itself.
    For the bar/dot mode switching, it's just a matter of which voltage level you're applying to the MODE pin (pin 9). Here it's just selected using a SPDT switch.
    The IC's been obsolete for a while though. You can't buy it from "legit" distributors anymore (like digikey, mouser, farnell, newark, allied, etc) . Either you'll find chinese fake/cloned parts, or old stock (most of which is gonna be fake/clone parts pretending to be new old stock -- from questionable chinese sellers on ebay/tabobao/aliexpress). 
    It would be better to implement this using a simple MCU but to do that you'll still need that analog stage. The voltage will still have to be rectified, and then amplified or divided to fit the ADC's voltage range (depending on your input level).
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    carlb got a reaction from spirilis in NewHaven displays 15% off on OLED boards   
    Cheaper, but not nearly cheap enough IMO. All displays are around $30. The monochrome ones (all 2.x inch) are similar, and cost a little a bit less if they have a lower resolution mainly. Color versions are the same price but are much smaller (1.x inch instead of the 2.x inch).
    Meanwhile, you can get great LCD modules for dirt cheap. For example, a 3.5" 320x480 color LCD (ILI93xx chipset, with HC595's to use it via SPI) and a resistive touch panel (with generic XPT2046 touch controller, which also uses SPI), for which you can find plenty of example code all-around the web... $10 on ebay (dirt cheap because they're mass-produced and sold for the Raspberry Pi), in single quantity, with free shipping too. 
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    carlb got a reaction from spirilis in edX course Real-Time bluetooth Networks - Shape the World   
    I just started it yesterday too. I'm kinda late to the party so I figured I'd try to catch-up as much as possible. I've done all of chapter 1 and lab 1 yesterday and watched all of chapter 2 today. I'll do lab 2 tomorrow.
    There was a LOT of material in chapter 2! None of it is super complicated but there's still a lot of it. It's great to see and understand how an RTOS works though! 
    I'll certainly go for the verified certificate like for the previous course!
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    carlb got a reaction from zeke in MSP-EXP432P401R Pre-Production (black PCB) LaunchPad to be Phased Out   
    I replaced all of mine (about 5 minutes of work each). I've confirmed that blinky works.
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