mirror of
https://github.com/taigrr/arduinolibs
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87 lines
4.2 KiB
Plaintext
87 lines
4.2 KiB
Plaintext
/*
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* Copyright (C) 2012 Southern Storm Software, Pty Ltd.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*/
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/**
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\file alarm-clock.dox
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\page alarm_clock Wind-Up Alarm Clock
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\section clock_power Power supply
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This section describes the power supply for the wind-up alarm clock,
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which consists of a hand-cranked dynamo, a 3.6 volt NiMH battery, and a
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charge pump DC-to-DC converter to boost the voltage up to 5 volts.
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Here is the circuit:
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\image html dynamo_power_supply.png
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The dynamo must be based on a DC motor rather than AC (bicycle light dynamos
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are typically AC). If you are using an AC dynamo, then replace D1 with a
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full 4-diode rectifier bridge to convert the AC into DC first.
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In Australia, <a href="http://www.jaycar.com.au">Jaycar</a> sells a suitable
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<a href="http://www.jaycar.com.au/productView.asp?ID=MD7000">DC dynamo</a>.
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Diode D1 stops the voltage in the battery from flowing backwards into
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the motor. If you hook things up the wrong way around, then the motor
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will spin without being cranked! In this case, reverse the + and - leads
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on the dynamo and try again.
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After D1, the main energy storage for the circuit is the 3.6 volt NiMH
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battery (at least 1000 mAh capacity). These are commonly used in
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cordless phones and can be obtained from most consumer electronics stores:
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\image html battery.jpg
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The main part of the circuit is next, consisting of a MAX619 regulated 5 volt
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charge pump DC-to-DC converter chip. This chip boosts an input voltage of
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between 2 and 3.6 volts up to 5 volts and regulates it into a nice flat
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supply for the rest of the alarm clock.
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Note: the MAX619 has a maximum rating of 3.6 volts, but when the dynamo is
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being cranked rapidly the voltage at the cathode of D1 can spike to 4 volts
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or more. The battery is fine with this for short periods of time,
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but the MAX619 won't be happy. Hence the forward voltage drop on D2
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is used to drop the supply down by 0.7 volts which will keep it within
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the MAX619's input range.
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For normal uncranked operation the battery will need to be between 2.7 and
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3.6 volts. If it falls below 2.7, then the battery is considered "empty".
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A diode with a smaller voltage drop can be substituted for D2 for longer
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operation times as long as the maximum dynamo output minus the voltage
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drop is less than or equal to 3.6 volts. The "Sense Battery Status" output
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is hooked up to an analog input pin on the Arduino to let it monitor
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the battery voltage and display the current status to the user.
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\section clock_arduino_board Arduino board
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Because we want to keep power consumption low, we actually don't want a full
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Arduino Uno or similar board. The USB interface is unnecessary, as is the
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on-board power supply. We also don't want the power and D13 status LED's
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to be draining power. Therefore, a cut-down version of the Arduino is
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recommended. We used the <a href="http://www.freetronics.com/collections/arduino/products/kitten">KitTen</a>
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kit from <a href="http://www.freetronics.com/">Freetronics</a>, and didn't
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solder up anything that wasn't strictly necessary. A
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<a href="http://www.freetronics.com/ftdi-cable">5v FTDI USB-to-Serial cable</a>
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is necessary for programming. Similar minimalistic built-it-yourself
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Arduino designs should also work.
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*/
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