[Fritzing] Circuit help for buttons

I'm a little stuck adding in the mosfets. It's doing my head in. I'm missing the ground to arduino and fear I've got the polarities mixed somewhere around the mosfets. I might also need to switch back to 5v for a mosfet?

Here's where I'm at so far:

Good try at layout, this might look easier to read, we learn as we go.
NOTE, use 12Vdc to 5Vdc converter to power the Nano, easier and simpler.

What I haven't added, if it is to go into a motor/mobile application is some bypass capacitors.

NOTE, You don't have 12V LEDs, you have LEDs with separate current limit resistors.

Tom... :smiley: :+1: :coffee: :australia:
PS. Everybody feel free to add/remove/like/dislike the schematic.

It's like a compromise between a circuit's logic and the physical layout. I think I understand it.

You don't have 12V LEDs, you have LEDs with separate current limit resistors.
I just thought if I wrote that, it'd imply the resistors are built in.

I'm really worried about finding a suitable mosfet.

These are all the ones I can obtain locally:

I read the datasheets, but from my understanding - the gate source voltage should be 5v?

Unfortunately Jaycar do not appear to have a LOGIC LEVEL MOSFET N-CH, you need to look for Vgs(th) of below 3V, 2 to 4 means that the MOSFET may not completely turn ON with 5V on the gate.

This one from Altronics is better.

Z1123.pdf (85.7 KB)

What will eventually be the load for the MOSFETs?

Tom... :smiley: :+1: :coffee: :australia:

Cheers, so a 3V gate requirement allows a 5V power source to more reliably create a connection?

What will eventually be the load for the MOSFETs?

That is a very good question I'm not able to test just yet. I suspect it'll be 250-1A.

I've bought the mosfets, it'll take around 3-4 weeks to arrive. I'll use a reed until they do.

Most people don't understand the purpose of fuses. A fuse close to the battery only protects the battery. Fuses protect upstream.


Can you clarify what you mean by 250-1A ?

The fuse is not to protect the electronics, it's to protect the cabling and the battery. Most batteries of whatever chemistry can easilly produce enough current to heat cables enough to start a fire. Some batteries, especially lithium batteries, will catch fire or explode if you short them out.

I think you mentioned high DC voltages, 60V and 72V if I read correctly. You should use HRC (high rupture capacity) fuses for this because when you interrupt DC you get an arc, which allows the current to continue flowing, this is particularly true above about 24VDC. HRC fuses have sand in them, the sand quenches the arc.

I suggest a fuse of 0.5A to 1A based on your description.

Perfect, thank you. For now I'm using the built-in 12v adapter - using the output intended for the headlight. If I draw too much current - I'll have to put in my own 60v to 12v step down.

250ma - 1a sorry.

Amperes are an SIU unit that should be capitalized.

Yes, it's interesting. SI units that are a person's name should be capitalised in symbol form (e.g. 'A' for Andre-Marie Ampere, 'V' for Alessandro Volta, 'J' for James Joule), whereas those that are not a person's name should be lower case ('m' for metre, 's' for second).

When spelled out they are always lower case: amps, volts, joules, metres, seconds).

Unless, it begins a sentence. But you knew that. Just so I'm off the hook.

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Depend on the voltage.
For 5V, I had I think chosen 10K adjustable resistors and even if I crank them to the highest resistance (10K) they are still too bright that I think they might be slowly burning out.
For 3.3v(a.k.a. 3v3), I had chosen 20Ks and, depend on color (i used red, green and blue), I end up somewhere in the middle. So maybe 10K.
Yeah, it's a bit dim, but the LEDs will live for quite long in that state.