Hey there!
First time that I'm posting here, but I've been struggling with some things that it feels like I've been in too deep. I would really appreciate any feedback and answers (or just a nudge in the right direction) for questions that I have!
I'm trying to hook up three muscle wires and three LEDs to the Uno (this will change to another board later, but this is what I'm starting with), but I'm struggling with setting up the muscle wires. The three muscle wires have the strongest pull when they get 1.5A (with 5V), so I'm planning to hook up a power adapter to it.
The power adapter is going to provide 5V. The muscle wires won't be on at the same time. For the muscle wires I intend to use mosfets.
I have three questions:
Do you see any problems with the diagram as it is now?
Do I need these specific resistors to handle the amount of watt? I've never had to look at this before, but I was looking at resistors that have this low amount of ohm, and it also told the amount of watt it could handle (at least that's what I've assumed). I've linked the resistors I was looking at in the component list.
If I want to connect the Arduino to the power adapter, what do I need to add in between? I feel like the diagram I've set up now should cause a problem, but I'm not sure what it is.
Here are links to the components that I want to use:
Just a quick note, I'm self-taught, so even though I researched a lot, I feel like I'm missing some theoretical knowledge. If you have any advice, it would be appreciated!
Great job on posting especially the schematic and links. I am not sure what you are trying to do but I will guess and trying to pass current to make the "muscle wires" flex. The MOSFET should work fine. There are several items that concern me as I do not know what the final results are to be. First your output from the Arduino will be dissipating to much power in the MOSFET unless you are doing pseudo current sink. If so disregard the next statement. Place the 3.3 ohm resistors on the drain in series with the "muscle wires". Connect the source to ground. If this is the way you want it your resistance calculations are right on at 12.2 Ohms per meter for the "muscle wires".. Connect the port pin to the gate of the MOSFET with maybe a 50 Ohm resistor and place a 10K resistor from the port pin to ground, this guarantees the state during reset etc. The gate resistor is to prevent oscillation especially with inductive loads. This does not happen a lot with the newer MOSFETS but it solves the problem. It also limits the current into the microprocessor port pin. The schematic is right on!
I agree with @gilshultz. Here is how to wire the MOSFET. I use 180 for the gate resistor, 50 Ohms should be OK as well (whether to use a gate resistor at all has been hotly debated).
The inclusion of the gate resistor is to limit the current that flows into the gate to charge the gate capacitance. That is the only time that current flows into the gate and it is pretty brief. So many people say that without the resistor the heating caused by that brief current out of the Arduino output is not enough to harm the output (that is my understanding of their argument). As a hobbyist, I generally try to err on the side of caution hence I use the gate resistor.
Google "N MOSFET switch". Virtually every page shows the MOSFET on the low side. The N MOSFET needs to be on the low side (source connected to ground) to be correctly biased.
