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Bluetooth and Amplifiers

Bluetooth AmplifierAll of my audio projects involve bluetooth and amplification. This can be two separate boards, or a single integrated one. The amplifers are all compact and energy efficient class D (3-15w). The amplifiers can produce a surprising amount (time and db) of good sounding music from a single 18650 battery (stepped up to 5 or 9v). The speakers I have been using are all pretty small, 45 - 55mm (~1-3/4 - 2-1/4"), with relatively low power ratings (3-7w). It's fun to see how far I can crank it up with the larger amps, but I'm happy with three watts and the pictured 2 x 3 watt bluetooth amplifier board makes it easy... more
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18650 Batteries

18650 BatteriesLithium-ion 18650 rechargeable batteries can store a lot of energy, but nowhere near what many eBay sellers are claiming. As of this writing, the maximum real capacity is 3600mAh - any claims over that are BS (e.g. 9900mah Etsair's).

I knew that when I bought my first 18650, but the SkyWolfEye "5000mAh" battery (eBay pic) with charger was dirt cheap. I then got what looked like a generic "2200mAh" because it was a realistic number (also cheap). I wouldn't have bought it had I known it was labeled UltraFire (most are fakes).

Wondering how to tell what the real capacity of my batteries was, I found that the weight of the battery is a good indicator. While somewhat informative, I wanted to know more after winning an auction for a couple of Cooligg 2500mAh batteries... more
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DC Converters and Chargers

DC Converters and ChargersWorking with low voltage direct current can involve batteries and/or multiple voltages. Changing voltages is accomplished with step-up and/or step-down voltage converters. Some converters are also capable of charging batteries. My current uses for these boards involve charging 18650 batteries and converting their 3.7 volts to 5, 9 and 12v. Following is some information on some of the various boards I have used... more
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Cord Control

Cord ControlWhy is it that cord management isn't built into everything that needs a cord? Things like wall warts would be a lot tidier and easier to use if there were a built in way to shorten and store the cord. Following are some of my aftermarket solutions... more
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RapidTables Watts Volts Amps Ohms Calculator
Use any two known values to calculate the other two, e.g. enter volts and amps to calculate watts and ohms.
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Digi-Key Battery Life Calculator
Calculate how long your battery will last at a given load (the milliamps your device consumes)
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