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Jan Visser
Jan Visser 3 hours ago
you can find the software here: https://www.elektormagazine.com/magazine/elektor-201707/40501  
nWatch - build and program your own smartwatch [160326]
Jan Visser
Jan Visser 3 hours ago
you can find the software here: https://www.elektormagazine.com/magazine/elektor-201707/40501  
nWatch - build and program your own smartwatch [160326]
Jan Visser
Jan Visser 3 hours ago
you can find the software here: https://www.elektormagazine.com/magazine/elektor-201707/40501  
nWatch - build and program your own smartwatch [160326]
Russin Sir Bullar
Russin Sir Bullar 4 hours ago
OK, I get it !   I thought it should be a lot easier to just use AVRDUDE to get the program into the Atmel-AVR /RISC single-chip microcontroller .   I realize now that it is not.  Compiling the original code in the Arduino IDE and then uploading to the atmega32u4  is safer and less "steps"  .   
180348 DIY soldering station
TonGiesberts
TonGiesberts 4 hours ago
For those who like to experiment I suggest replacing IC3 with a TL062BCP (available at Mouser 595-TL062BCP). It has a typical offset of 2 mV and 3 mV max. The AD648 can be a good replacement, only minimum power supply is specified as 9 V minimum and slew rate is half compared to a TL062 (AD648 is only specified at +/-15 V). So only works with a fresh battery. Hard to say how the opamp performs when the battery voltage drops. Another option is perhaps a LT1352CN8#PBF, although a bit expensive. It has a high slew rate (specified as 21 V/µs at +/- 5 V) but is unity gain stable. The only problem with this one is a high bias current, 20 nA typical and 50 nA max. This will cause an additional offset across R22 of 2 mV (but also across P2, depending on its setting). Some resistors must be lowered in value than, at least by a factor 10. Recommendation: R21 1kΩ, R22 10 kΩ, P2 10 kΩ, R23 100 kΩ. And capacitor C21 must then be increased to 10 nF. Not tested!   When considering using another opamp for IC3, make sure that slew rate is at least equal to the one specified for a TL062 (3.5 V/µs), quiescent current is about 200 µA and power supply is specified between 6 V and more than 9 V max. Microchip has some interesting opamps but almost all have a maximum power supply of 5.5 V abs. max.
Bat detector with amplitude recovery