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/*
* waterlevel.pde - water level measurement with shift register
*
* Copyright (c) 2010 András Veres-Szentkirályi
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*
*
* Shift register used: 74HC299
*
* Connections:
* Arduino Purpose 74HC299
* 2 CP 12
* 3 Q7 17
* 4 S1 19
* 5V Vcc 1,2,3,9,20
* GND GND 10
*/

#define CP 2
#define Q7 3
#define S1 4

#define LOAD HIGH
#define SHIFT LOW

void setup() {
pinMode(CP, OUTPUT);
pinMode(Q7, INPUT); /* no pullup by default */
pinMode(S1, OUTPUT);
Serial.begin(9600);
}

void loop() {
Serial.println(getLevel(), DEC);
delay(1000);
}

void pulseClk() {
/* 74HC299 can handle up to 50 MHz @ 5V */
digitalWrite(CP, HIGH);
digitalWrite(CP, LOW);
}

void execCmd(byte cmd) {
/* S0 is pulled high, so S1 = HIGH loads, S1 = LOW shifts right */
digitalWrite(S1, cmd);
pulseClk();
}

byte readReg() {
byte retval = 0;
execCmd(LOAD);
for (byte i = 0; i < 8; i++) { /* read bits one by one */
retval = (retval << 1) | (digitalRead(Q7) == HIGH ? 1 : 0);
execCmd(SHIFT);
}
return retval;
}

byte getLevel() {
byte retval = 0;
for (byte i = readReg(); i; i >>= 1)
retval++;
return retval;
}
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