cascaded switchingof a solenoid valve

living with the lab

transistor relay solenoid valve

© 2012 David Hall

living with the lab

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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 opencontacts

SPST relay

solenoid valve

+ -

12VDCpowersupply 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

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• 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

5V

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 considerations1. Power to switch transistor

source:max current per digital I/O pin:

2. Power to switch relaysource: max current from the voltage regulator: coil current for relay:

3. Power to switch solenoid valvesource: 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

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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

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5V

12V

living with the lab

more compact wiring you will need three relays, two for the solenoid valves and one for the heater

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transistors turned with round side toward relays

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view from other side of relays

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stripes on diodesmust point towardpositive voltage

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another view

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living with the lab

complete assembly of conductivity control system(in class or for homework, as time permits)

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