Great thanks!

 

Ok then! Thanks!

I still don't understand what that does?

The pull-down resistor holds the gate low when the micro-controller is not driving it (such as when it is first booting up and the pins haven't been setup yet). Otherwise the gate can (and probably will) "float" high and turn on the MOSFET.

 

I'm going to build the circuit then ! Thanks for your help

 

Sorry, I have another question!

If I wanted to have small LED that lights up when the +5V 'trigger' signal is present,
how would I connect it, so it doesn't draw too much power(and keeps the MOSFET
from its full potential) ?


Thanks!

 

Sorry, I have another question!

If I wanted to have small LED that lights up when the +5V 'trigger' signal is present,
how would I connect it, so it doesn't draw too much power(and keeps the MOSFET
from its full potential) ?


Thanks!

Just insert the LED with an appropriate series resistor between the trigger signal and ground.

 

Hi guys!

I need to drive two solenoids(or the like), so I made another circuit. The
second one has +5V and GND(trigger) from another output on the uC.
These two circuits and coils looks like the image above x 2

This is still the circuit:

But when one coil energizes, the other does too since the GND is connected.
The +24V from the power supply is connected to the banded diode side of
both coils, and the un-banded side of both is connected to GND on the PSU.

How can isolate this, so I can control one circuit and coil at a time?
So how should I use it with two identical setups from the same PSU?

Thanks for your time!

(tracecom, thanks! Got the LED to work)

 

That doesn't seem right, it should work correctly the way it is now. Can you post a picture of your setup?

 

Hi again

I made another drawing. Right now I'm using a keyboard encoder I had lying around,
to get signals out, one for caps-lock and one for num-lock. That way it's only
hardware I have to think about right now

I want this to be two identical circuit 'boards' each with a coil/lamp, that is
connected to the same +24V source. Since the gnd is connected all over, I get
that both is activated when one should be. So I need to isolate it, or whatever it's
called.

Here's the picture:

http://www.popbumper.dk/mosfet4.JPG

Any advice? I have a feeling that it's something trivial I did wrong.

Thanks!

 

That looks correct, but if you have a problem wiht both coils activating at the same time, get rid of that keyboard controller and use some stnadard 5V supply instead to control the gates. Also measure the 24V voltage when before and after you activate them.

 

Hi.

My lab supply has a preset +5V output, with that connected (and gnd) the same
thing happens. The 24V is good, coming from the same lab supply.

Still, when I look at my own drawing doesn't the 'caps lock' input connect to the
'num lock' input, and cause both to energize?

There must something wrong with the way the circuit is made

 

I assumed the wire where you write caps lock output is actually connected to ground of the 5V supply and the point with 5V written is the input, right?

 

Yes, the caps lock 'signal' is gnd and the 5V is from the 5V output

 

Regarding using the encoder, here's a picture of the output. I take the +5V from
here to the gate on the mosfet and the 'caps lock' line to the 'caps lock' input
next to the +5V on my circuit. So, the +5V is on all the time, and the caps lock
output is grounded, yes?

 

I don't know what you are doing with the keyboard controller, but if you build two identical circuits as shown in post number 26, there should be no interaction between them. Start by eliminating variables. Instead of the keyboard, use the 5V output applied directly to the 10 Ω gate resistor of each circuit.

Here's the schematic and a photo of the breadboard. Notice that I am using +5V as the trigger and 12V to light the LEDs, but the principle is the same as you are attempting.

 

Thank you very much for that! Even building the circuit

I think I understand something now. On the keyboard
output, the 5V is on all the time, and the gnd is the thing that
signals....so, it's like if your circuit has the 5V on both gates all the
time, and then you touch the gnd to turn it on...then both energize
at the same time.

So is it correct to say that I need the gnd to be the signal, and not the 5V?
Can I use something like a TTL inverter or the like?

Thanks!

 

No. Do you see R3 and R4? That is what keeps the ground level on the gate when nothing is connected. You need to connect +5V to R1 or R2 to turn the transistor on.
You even have it written in the picture itself.

 

Here is a schematic modified to be triggered by a ground signal as opposed to a +5V signal. I have used a 2N2222, but any small NPN transistor should work.

I realize this is not the best way to accomplish what the OP wants; a P channel MOSFET might be the better choice. But given that he already has the N channels, this seems to work.

I would appreciate a review by other, more knowledgeable forum members.

 

That looks correct. I would just change R11 and R12 to 47k to be more sure the transistor is in saturation.

 

Thanks for that circuit, that is awesome.

I hope I can ask - for learning purposes - about something. On the keyboard controller
the output I use is at 5V, when caps-lock is not active. When it IS active, the
voltage goes to 0V. That's why I ask about the inverter, like a 7404 hex inverter.
I would then connect that inverted output to the +5V gate input on the original
circuit. I know it's the same outcome as the circuit in post # 37, and I have both
7404's and 2n2222's.

tracecom, I know it's a lot to ask, but if the inverter thing is incorrect, could
you please make the circuit in post #37 as a single-circuit? I have a feeling you
can make it much more tidy than me

Thanks guys!

 

You can use an inverter instead of the 2n2222 circuit. What´s the problem with redrawing it for a single switch? Just start with the wire going to the LED2 label and cross out every part the is connected to it, then everything that was connected to the crossed out part, and do it ad nauseum. Obviously the 5V, 12V and GND rails have to stay, when you reach those that´s where you stop deleting next parts.