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Topic: Q on turning a relay on while turning one off at the same time (PNP transistors) (Read 4159 times) previous topic - next topic

Zeeko

Hey all,

I'm using a Sainsmart 16 relay module, and relays turn ON when I send LOW voltage signals from my Arduino ports to the control pins on the board. 

That said, I'm controlling a 12v water valve that uses TWO signals- one to open the valve, and a separate signal to close the valve... It needs two relays that are always doing the opposite thing.  I want to conserve a digital pin on my Arduino and do two things at once using a transistor... where if I want water, the opposite signal is sent to the OFF relay.  something like:

If I need my water valve to open, I send a LOW signal to the pin/relay to the water valve OPEN relay, but at the same time, that low signal CLOSES a 5v circuit, that turns my water valve CLOSED relay to HIGH (aka turning my water valve CLOSED relay... OFF. . 

It's a really weird circuit and I don't thing an NPN is going to work... Can anyone tell me if a PNP is the right way to go/which one I should purchase? 

Thanks!

Z

larryd

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Zeeko

I'll get cracking on that  :o  But to maybe put it more simply, if I am say...  powering an LED between my Arduino's 5v and ground, how can incorporate a digital output signal that keeps the LED circuit closed when digitalWrite(3, HIGH) and opens the 5v circuit (turns the LED off) when I send a digitalWrite(3, LOW) signal? It seems to be sort of the reverse of an NPN transistor. 

CrossRoads

NPN and 2 resistors, all you need:
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Zeeko

Okay, this is my first schematic  :o but I think it kind of alludes to what I want... I want the transistor to open the circuit when a signal is sent to it so that only one of the two relays activates at once.   

CrossRoads

Simpler design:

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Zeeko

That's a pretty nifty solution.  What size resistors/transistors would you recommend?

Wawa

I'm using a Sainsmart 16 relay module, and relays turn ON when I send LOW voltage signals from my Arduino ports to the control pins on the board.  

That said, I'm controlling a 12v water valve that uses TWO signals- one to open the valve, and a separate signal to close the valve... It needs two relays that are always doing the opposite thing.  I want to conserve a digital pin on my Arduino and do two things at once using a transistor... where if I want water, the opposite signal is sent to the OFF relay.
Can't you use two relay channels for that.
The NO contact of one, and the NC contact of the other one.
AFAIK a 16-channel relay board uses 3.8mA drive current per channel, so you can drive up to 5 channels with one Arduino pin.
Leo..

Zeeko


Paul__B


TomGeorge

Hi,
Can I put a spanner in the works, can the OP post link to the spec of the solenoid.
If it is low voltage 12v, you only need to PULSE the solenoid to change state, they are designed for low energy use.
Constant drive current may not do the solenoids any good.
How much current does the solenoid use?
How many solenoids in a valve, one or two?

Can we have the part number and or specs please. 

Tom..... :)
Everything runs on smoke, let the smoke out, it stops running....

MarkT

Hey all,

I'm using a Sainsmart 16 relay module, and relays turn ON when I send LOW voltage signals from my Arduino ports to the control pins on the board. 

That said, I'm controlling a 12v water valve that uses TWO signals- one to open the valve, and a separate signal to close the valve... It needs two relays that are always doing the opposite thing.  I want to conserve a digital pin on my Arduino and do two things at once using a transistor...
That may be impossible.

The valve may be designed such that each coil can only be operated intermittently without
overheating, not continuously.  You need to provide a link or datasheet about the valve.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

Zeeko

edit: double post

Zeeko

I like putting spanners in the works.  Here's a link to the valve in question: 

http://www.aliexpress.com/item/1-2-Mini-electric-valve-3-wires-CR02-DC12V-motorized-ball-valve-SS304-DN15-electric-automatic/1941185157.html

It's a 3-wire, it sounds like it takes 3-5 seconds for a change in mode (open to close and vice versa) and the valve says MODE: CR-02 on the top.  This is a diagram of the CR-02 Wiring:



MarkT

That's a motor operated valve designed for single
relay control judging from the image (the link is broken for me though).

You will find it is encouraged to provide full information about hardware up-front, since
you get much quicker and more reliable answers to your question that way.

That wiring diagram explains that you use a SPDT switch or relay to control the thing.
It seems pretty clear to me.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

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