# Fuse burnt out

Hi guys,

there is a binary signal that I want to set to High. I measured that on High bit 24V flows on that pin, which is much more than my Mega2560 can afford. So I connected my Digitial Outpin with a voltage converter. With a multimeter I could measure that when I send digitalwrite() a 24V flows. So I just attached this to the port hoping that this could set the High bit. But boom…fuse burnt out. Did I miss something here? A resistor?

Attached you can find a circuit diagramm. DV1 is the port that I want to set to High. I disconnected the line and attached my arduino to there.

Use a voltage divider. Only 2 resistors.

Could you explain more in detail…?
I have to raise 5 V digital Output to 24V. Why should the 5v be divided?

It's slightly-strange that a fuse blew but I'd guess you're not supposed to feed 24V into that point. Usually when a fuse blows, some other component has blown/shorted-out. Is the thing still working as it used to without the Arduino? Is the Arduino still working?

So I connected my Digitial Outpin with a voltage converter.

What voltage converter? The Arduino output pins are 5V, low current signals. They don't provide "power".

You need a 24V power source that you can switch on/off through a transistor, MOSFET, or relay controlled by the Arduino You might be able to use a step-up converter from the Arduino's 5V supply depending on how much current you need.

Note that a 24V step-up converter will "pull" at least 5 times as much current from the 5V supply as you're getting out at 24V.

But if that circuit needs 24V, I assume there is already 24V power available somewhere on the existing circuit?

I have to raise 5 V digital Output to 24V. Why should the 5v be divided?

DVDdoug:
Is the thing still working as it used to without the Arduino? Is the Arduino still working?

That thing is still working after replacing the fuse and the arduino also survived

DVDdoug:
What voltage converter? The Arduino output pins are 5V, low current signals. They don’t provide “power”.

However, if a pin outputs 5V (when I set it HIGH), why cant I just it as a provider? With digitalWrite(HIGH / LOW) we can even simulate switching function.

DVDdoug:
depending on how much current you need.

Since I measured that 24V on the pin DV1, when it was HIGH, I need 24 V.
Finally, I want to set the DV1 to HIGH. Thats all I want to do.

DVDdoug:
But if that circuit needs 24V, I assume there is already 24V power available somewhere on the existing circuit?

Yes 24V is on the existing circuit. Pls have a look at the attached file.

So what do you think of the reason of this “fuse issue” ? Anything wrong with my circuit?

You appear to be powering the MT3608 from the Arduino digital output. That won't work.

The Arduino must control 24V coming from another source. The MT3608 might be powered from the Arduino 5V or Vin power supply to provide 24V if you don't have 24V power available from the rest of the circuit.

But whats the reason that digital Output cant be a power source?
Because it does not always provide 5V ? ( when I keep it HIGH all the time, then it is like a constant 5v supplier?)

Because it can't safely provide more than 20mA. That's a tiny amount of power.

The MT3608 chip is specified to use 1.6-2.2mA and the rest of the components on that module can only increase the power it's using. Then the conversion is inefficient and the higher voltage means lower current for the same power and you only get 3 or 4mA out at the other end and that's with the Arduino working as hard as it can.

xman236:
But whats the reason that digital Output cant be a power source?
Because it does not always provide 5V ? ( when I keep it HIGH all the time, then it is like a constant 5v supplier?)

It can be a power source. But the maximum amount of power that it can supply (if needed) is relatively small --- which is a result of design --- ie. the way that the designers of this board intended it.

Take one well known expression for power .... voltage times current. The designer often tells you what power level (eg. output power level --- product of output voltage and output current - for a supply) should not be exceeded. A decent designer also tells you want voltage should never be exceeded, and what current should never be exceeded. Exceeding the 'rated' power level might/could lead to damage of some sort..... it may or may not. No guarantees. The thing is..... a supply usually has ratings... power, voltage, current etc. And those values might even be specified for certain temperature of operation etc.

Whatever is the case..... most electrical/electronic/mechanical/electro-mechanical devices or equipment have operational limits. It's just up to the user of the device to understand those limits.

The main issue was basically using something without all the correct important 'assumptions' about it. It is like using something without reading the manual or full understanding of how to use it. That's why reading lots of tutorials and starting from the basics will be beneficial. And...... if there are no tutorials (online, or anywhere) for novice level that show the same kind of setup as the one you attempted, then it's likely that there's a good reason for it. eg..... it's probably not going to work.