![]() The “K” factor represents the slope of the fitted line and has a dimension of pulses per unit volume moved. These are plotted but since the turbine has some friction, the graph will not be linear especially at the low end and a linear regression is done to get a best fit straight line. During calibration the manufacturer measures the pulse rate outputs for a number of precise flow rates. The opposite side of the box has a simple on/off slide switch mounted.Īlmost all of the turbine type flow sensors I looked at have two calibration factors specified: a “K” factor and an “offset”. If the sensor is a 3 wire type, the pulse lead connects to the plug ring Connection to the sensor plug is as follows: There is a power jack for 9 or 12 volt DC input, and a 3 conductor phone jack to connect the turbine sensor. If I have to build another one of these, I might glue the Arduino board to the back of the LCD which will greatly reduce the wiring between lid and box. I attached a 10k Pot for contrast adjustment to the back of the LCD and it’s legs are used as tie points for 5v and ground wiring to the rest of the display. The screw heads are soldered directly to the lid. The Liquid Crystal Display itself mounts on four 2-56 screws. That capacitor is part of my debounce strategy. ![]() It’s hard to see, but there is a 0.05 ufd surface mount capacitor soldered between the signal side and ground. Note the bit of PC board on the high side of the switch has a groove filed across so the grounded paper clip is isolated from the signal connection. This photo shows the LED and the Reset button. I solder one side directly to the lid, the other side of the switch is supported by a bit of PCB material and a piece of paper clip wire. An LED and two push buttons protrude through the lid, these are regular 6mm square PCB buttons. It takes up little space and has a 5 volt regulator with enough capacity to run the 16×2 LCD. The Arduino variant I used is a Sparkfun Pro Mini 5 Volt. When satisfied with the results, I went ahead with building the Altoids tin prototype. The same technique anchors the Arduino board.Īt first I worked up the circuit on a solderless bread board using code from the Adafruit web site. I use “L” shaped bits cut from a paper clip, soldered to the board ground, and to the ground plane. In this photo you can see the interface board soldered down near the front of the Altoids tin. It’s a bad thing to overvolt an Arduino pin, please Don’t Ask Me How I Know This. A series resistor and zener diode make sure the voltage ratings of the Arduino input pin are not exceeded. The series resistor value is low enough that the power feed is still adequate for the small plastic sensor, so the option jumper just selects where to pick off the pulse signal. The positive supply feeds through a resistor which produces enough voltage drop when the large sensor is pulsing to trigger a digital low at the Arduino. I constructed the interface circuit on a small piece of project board from Radio Shack (RIP). I designed an interface circuit that works with either unit by changing an option jumper. The display must sense a pulse by looking for an increase in supply current. It signals a pulse by shunting power to ground through a low resistance. The electrical interface on the small flow meter has 3 wires, power, ground, and pulse output – relatively simple to connect to the microcontroller. Flow Sensor Prototype with Large Flow Sensor
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