# Basic circuit help

Hello everybody,

I am new to electronics and have been toying around with the arduino for about a month now. I have played with simple things like servos and motors but I have decided I wanted to make something of actual use to me. My problem is I have a relatively weak understanding of how to build proper circuits.

My want is to use the arduino to control a 12VDC solenoid valve and a 12VDC linear actuator. I was thinking of using transistors to control each of them, but am not sure if it is the best way or even feasible to control them in this manner. I also am unsure of what to use as a power supply, I was thinking a wall plug via something like a computer power supply. Thanks for any help you can give!

Well the spec sheet for that actuator recommends protecting the actuator with a 10 amp fuse, so that implies that your external +12vdc power supply should have a simular or higher current rating. The solenoid valve most likely takes an amp or less as a guess, but no spec sheet was shown. Look around E-bay or surplus on line vendors for a large enough power supply.

One way to control these with an Arduino is to use a LOGIC LEVEL N-channel MOSFET transistor. The one for the actuator should be rated at least for 50vdc or more and 25 amps or more.

Lefty

Thanks for the quick reply, I have looked around the web and found 2 I think may work. I was also wondering whats meant by LOGIC LEVEL, the rest I understand, I did a quick google search and couldn't find anything.

I was also wondering whats meant by LOGIC LEVEL, the rest I understand

Logic level means the gate of the MOSFET can be controlled by logic-level signals. Both of the MOSFETs you linked to seem good in that regard.

But I have a question myself: if I understand things right, a logic-level MOSFET has a gate-threshold voltage of 5V or below, right? So, I have seen these “logic level” MOSFETs (including the ones linked) that have a min-max value for the gate-threshold voltage of between 1.0-3.0 volts.

Won’t this be a problem with the Arduino, or any other device which is using TTL logic levels (5V = HIGH)? Or am I missing something (which is more than possible)?

Depending on this answer, then, those MOSFETs may or may not be suitable…

if I understand things right, a logic-level MOSFET has a gate-threshold voltage of 5V or below, right?

No. The gate threshold voltage spec is the voltage where the mosfet just starts to conduct, it's a more useful spec when using the mosfet as a linear amp rather then as a switching device. A normal mosfet might have a typical gate threshold rating of 4-5 vdc, but requires a full +10vdc gate voltage to fully turn on.

Logic level mosfets mean the the device can conduct full rated current at a logic voltage (4-5v)on it's gate. One really should look over the device's data sheet at a graph that shows gate voltage Vs source/drain current flow to see if the device will work with the load you will be using, with the gate voltage avalible.

Lefty

One really should look over the device's data sheet at a graph that shows gate voltage Vs source/drain current flow to see if the device will work with the load you will be using, with the gate voltage avalible.

Thanks for the reply - that makes sense; I looked at those datasheets again, and the graphs - they should work OK.

Can you recommend a tutorial or something that covers all of this (I've found plenty of things on how to select a BJT, but not as much clear explanations for MOSFETs)?

:)

Awesome retrolefty and cr0sh, I am understanding this stuff way better now. I too would be interested in a tutorial or literature that overs the topic a little more. I ordered the transistors and now all I have to do is wait for them and build my first h-bridge. Thanks for all your guys help!