Vcc Switched Solenoid Control

I need to control some remote solenoid valves. I’m aware of the standard answer for this: http://arduino.cc/playground/uploads/Learning/solenoid_driver.pdf

Because these are located 10+ft from the controller I do not want to have power running to the valves at all time. There is just too much danger of a short or accidental grounding. Instead I want to switch the current TO the valves. There doesn’t seem to be much information on setting things up this way.

I did come across this example but it seems like there has to be an easier way to do this. I need to control 4 valves which means making this 4 times. Are there any other options?

why do you have two transistors? the FET that you have is voltage triggered, and will therefore probably be always triggered (there is only a resistor in the way of power). As for making it 4 times: You can get P-MOSFETS. Then, when the micro pin is low, the P-FET triggers (because it is "inverting"), and when the pin goes high, it turns off and the N-FET turns on.

baum

That is a diagram I found not mine: ) As you noted it seems overly complex to me, like there must be a easier way. I should have noted that each valve will be controlled independantly by the Arduino which is why I'm thinking that I would need to build this circuit 4 times.

So you say I shoudl be able to control the circuit with a single P-MOSFET and no need for Q1 in that diagram?

You can buy what's called a "load switch", which is essentially the circuit you drew packaged in a single IC. For example the NXP PBLS2002S contains an NPN and PNP transistor in a single SO-8 package:

http://www.nxp.com/documents/data_sheet/PBLS2002S.pdf

You still need one of these for each relay though.

-- The QuadRAM shield: add 512 kilobytes of external RAM to your Arduino Mega/Mega2560

RC,

I could deal with that device even if I needed four of them. Do you know if them make them in a nonSMD formfactor? I looked around at some others and they all are SMD which makes testing on a breadboard a bit of a problem.

Nope, don't know of any through-hole devices like that. You could always get some breakout boards from Schmartboard or something to make the devices more breadboard friendly.

-- The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

I really wanted to avoid relays in this setup but it keeps looking like it's going to be my best option. It seems like this would be a common issue with projects that there would be a cleaner solution for.

What's wrong with transistors?

Nothing wrong with them but I'm not interested in building a 2 transistor to control each one of these valves. I was hoping that I could find a way to do it wth just one but so far I can't find a way to make it work :(

The way I understand it, you do not want the positive lead going directly to your solenoid. Instead, you would like your control circuit between the +voltage and the solenoid.

That being the case, you can simple put the solenoid on the Drain side of a FET instead of the source side. The solenoid will always be connected to GND/common but, will receive +voltage when the FET is activated similarly to how a pushbutton would connect the solenoid to +voltage.

The picture you posted shows how the solenoid goes in relation to the FET. However, as long as you are mostly just doing steady state off or on you can do it with a single FET and a couple resistors. I don't have a recommend part # but, I know you want one that can operate with a 5 volt gate.

That is exactly what I want to do but all the wiring examples I have found are with the load before the switching FET. If I can put the load after the FET. Then I'm happy!

This would be a plain N channel FET right?

I have the correct part at home, I will try to reply tomorrow if someone else doesn't answer before that.

N-channel 11.1Amp NTD4960n-35G

Digi-key# NTD4960N-35GOS-ND

Thanks.

I'll be ordering some today!

Looks like the NTD4809NH-35G-ND is just about all they have in stock... Unless I want to buy 2,000+ of them.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=107840173&uq=634584085109704477

Try mouser. They have it (as well as many other things; they tend to be more qty friendly than digikey).

baum

I am starting to doubt myself on whether you need the N or the P. Because you want the solenoid on the negative side of the FET, I think you may need the P channel. I would like someone to help out on that a bit.

I did however look for a couple fets that work with 5volt gate control.

Here is a P-channel mosfet http://www.sparkfun.com/products/10349

Here is a N-channel mosfet http://www.sparkfun.com/products/10213

The problem with a P-channel FET is that the gate needs to be as high as the V+. So you end up needing a regular NPN transitor to drive the gate to +12v to turn it on. Which puts me right back to the diagram that I had in the first post in the thread. Right back to needing 2 Transistors and 2 resistors for each of the 4 control circuits. Just seems so messy.

Anyone else ever try this with an N-channel FET?

I found an N-channel FET lying around and I was able to test the circuit design and it seemed to work. The FET I had wasn't the right type to work with 5v on the gate so the whole circuit was 12v but it did work. I have some 5volt gate FET's on order and hopefully they will be here tomorrow so I can test the actual 5V-12v circuit and see if it works like the 12v one did.