However, we did it, and this is how we evaluated each one. Trust us, it wasn’t easy trying to find these portable battery coffee brewers, and it was even harder to assess their performance to determine if they were worthy. I'm guessing about $0.25 a piece by the dozen, but, then, that's not an electronics engineering solution, so it wouldn't be as pertinent as the above here.6 FAQs How We Ranked Each Battery Powered Coffee Maker Or, hmm, much easier - buy some digital clocks or watches or timed alarms at dealextreme (dx.com) or or similar. Oh some regulators want a minimum load of a milliamp or two to regulate properly, so maybe run at 8MHz to satisfy that if needed or use a regulator with no minimum load required. Set the MCU to run at some frequency like 32kHz or 1MHz or 8MHz, doesn't matter much, just adjust the timing to suit the loop speed. Don't be debugging the MCU while checking the speed or it'll throw off the timing results. Start with a smaller number like 1000000L and see how long that takes and extrapolate from there. The code here will delay a while and then turn on the PORT1 bits which would enable the buzzer. You probably don't really need a capacitor across the battery, or, for that matter across the regulator 3V output though one is recommended there. Launchpad programming kit (might be a little cheaper at TI's web store if the shipping is still free there): Make a dozen or so PCBs at OSHPARK if you want to make the wiring easier.īuzzers that can work at 3V or some higher: More like $10 if you shop at radio shack, though they probably don't sell MCUs other than a $40 arduino kit or something. Should be about $5 or less worth of parts for the unit if you wire it up on protoboard and buy the parts at DigiKey. Put a 10uF 16VDC or higher capacitor as follows: negative = battery GROUND, positive = voltage regulator positive output. Put a 10uF 16VDC or higher capacitor as follows: negative = battery GROUND, positive = battery positive. Use the $4.30 TI MSP430 "Launchpad" named development kit to program the chip in a 14 or 20 pin DIP package. Program the MCU to generate whatever pattern of delays you want. Voltage regulator output terminal = MCU positive supply terminal and maybe also the buzzer positive supply if it is a 3.3VDC buzzer. Voltage regulator IN terminal = battery positive terminal, voltage regulator ground terminal = battery negative terminal. Use a NPN transistor like the PN2222 with emitter grounded, the base hooked through a 1K resistor to the MCU output pin, the collector to the negative buzzer lead, and the positive buzzer lead going to the positive battery terminal or the voltage regulator output depending on whether the buzzer takes 9V or 3.3V to operate. MSP430G2452 in a DIP pacakge), a 9V battery + snap connector + leads, and a 9V in 3.3V or 3.6V output voltage regulator for the MCU. One combination that comes to mind is the MSP430Gxxx MCU (could be any device in the series e.g. Microcontroller, buzzer/beeper/bell/siren device (you can buy them that make a variety of fixed function sounds once you provide a DC power source to them), battery, and voltage regulator for making the microcontroller / buzzer work given the battery voltage. Plus a breadboard and some jumper wires for programming. You'll need a USB programmer and a socket to program the chips in, which adds about $10 of one-time cost. The Attiny can be programmed to wait for a random amount of time, and then make a noise on the output pin that drives the MOSFET/speaker. 1 MHz (and perhaps sleep mode) will extend the lifetime, although you'll likely get a couple of days of battery life even without that. The Atmega can run on the built-in ceramic resonator at 1 MHz or 8 MHz when fed 3V or better. Simulate this circuit – Schematic created using CircuitLabĪn Attiny is about $1.
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