cascaded switching of a solenoid valve living with the lab transistor relay solenoid valve © 2012 David Hall

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wiring living with the lab setting digital output on Arduino HIGH switches the transistor the transistor allows current to flow through the relay coil, closing the relay contacts power from the 12VDC supply actuates the solenoid valve, allowing water to flow 3 5V C B E Arduino digital pin 1kΩ coil normally open contacts SPST relay solenoid valve VDC power supply diodes

C B E 5V Arduino digital pin 1k  C B E 5V Arduino digital pin 1k  good and bad wiring: using a flyback diode living with the lab 4

5V C B E Arduino digital pin 1k  why do we need a flyback diode living with the lab 5 when digital pin 8 on the Arduino goes LOW, the decay of the magnetic field induces a current that can be harmful to our electronics (can arc across contacts or send a surge through the system) the diode allows a circular current to be set up in the coil / diode loop so that the magnetic energy stored in the coil can be safely dissipated void setup() { pinMode(8,OUTPUT); } void loop() { digitalWrite(8, HIGH); delay(500); digitalWrite(8, LOW); delay(2000); } 5V C B E C B E Arduino digital pin 1k  current path broken when digital pin 8 on the Arduino goes HIGH, electricity is conducted through the coil of the relay, inducing a magnetic field in the coil energy is stored in the coil as a magnetic field

living with the lab power considerations 1.Power to switch transistor source: max current per digital I/O pin: 2.Power to switch relay source: max current from the voltage regulator: coil current for relay: 3.Power to switch solenoid valve source: max current of power supply: requirements of solenoid valve: Arduino digital I/O pin 40 mA 5V from Arduino (from the on-board voltage regulator) 800 mA 40 mA 12VDC wall power supply (converts AC to DC) 1.5A (depends on power supply purchased) 0.29A 6

living with the lab void setup() { pinMode(8,OUTPUT); } void loop() { digitalWrite(8, HIGH); delay(500); digitalWrite(8, LOW); delay(2000); } wire to digital pin 8 silver stripe toward positive side implementation solenoid valve 7 5V 12V

living with the lab more compact wiring you will need three relays, two for the solenoid valves and one for the heater 8 transistors turned with round side toward relays

living with the lab view from other side of relays 9 stripes on diodes must point toward positive voltage

living with the lab another view 10

living with the lab complete assembly of conductivity control system (in class or for homework, as time permits) 11