Keep burning out Arduino boards, problem with my circuit design?

Other Hardware General Electronics
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No idea what is going on, I'm very new with this and using this project as a way to learn electronics.

I put together the following diagram showing my circuit

robot gate
robot gate724×443 21.9 KB

So far I have burned out 2 arduinos while having it connected to 7.2v power source or USB. I suspect the problem is with my transistor / mosfet setup where I am then stepping up the voltage to 24v to run a motor, but I believe this should be isolated from the arduino.

2 of my arduinos get super hot now just when connected to power, 1 doesn't respond at all when connected to USB.

I can share code as well. Basically, I am using BLE to sense when my robotic lawnmower gets close to my fence, and when it does it opens up a gate to let it pass. The switch is for manual operation (mostly for testing). The LEDs are just for status. The resistors / A6 connection is for me to determine battery level.

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You are putting 7.2V into an NPN transistor emitter. The base is thus conducting 7.2-0.6V = 6.6V directly into pin D3 and destroying it.

Your circuit with the BJT and FET is wrong.

This is how it should be wired.
high_side_sw

Make sure the polarities of the devices are correct, and that the pFET turns fully on with 7V.

1 Like
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Thanks Mark, I'll make the changes, and hopefully that'll fix the problem. I didn't realize the voltage went back into the gate from the source. I guess that makes sense thinking it through.

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It doesn't, the gate is isolated. But the gate isn't the issue. The emitter and base of the NPN transistor are the issue. BJTs have base, emitter, collector and function totally differently from FETs (which have gate/source/drain)

  • where did you get that incorrect circuit from?
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Sorry, like I said beginner so terminology escapes me sometimes. I meant base. Why isn't the base isolated on a transistor, but the gate is isolated on a mosfet?

I designed the incorrect circuit myself (hence the incorrect part).

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Because they are totally different devices that work in completely different ways - you can learn about them if you want there are 1000's of resources out there. The names reflect this difference, "bipolar junction" v. "field effect".

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The point of the transistor was to step up the voltage to the gate of the mosfet. Since the pin outputs 3.3v, the mosfet I am using (irfz44n) requires 5v to partially function, and so I am trying to put the full 7.2v into the gate to allow the current to drain properly. I'm using a PNP transistor (MPSA92)

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and I just looked up the difference of npn vs pnp transistor, and npn is definitely the way to go :slight_smile:

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So you're an Electronic Design Engineer now ?
Wouldn't it have been better to accept the fact that you have no design experience and post before testing ?

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There's always a temptation to guess and try, but experience will tell than "measure twice, cut once" applies to electronics too, though more along the lines of "check everything twice, initially power up with current-limiting bench supply"

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Sure, but less fun. Exploration is a fun way to learn. I make mistakes, burn out a few arduinos, then spend the time to try to identify and fix the problem. Since I hit a point where I couldn't identify the problem, now I post.

2 Likes
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You know what they say:

Experience Varies Directly With Equipment Ruined.

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Or, put differently, "Good decisions come from experience, experience comes from making bad decisions..."

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I hope your credit card has a high limit.

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Hi,
What is your 7.2V supply, how much current can it provide?
What is your 24V motor, can you please post link to specs/data?

What is your DC-DC converter?

Your potential divider 200R and 150R could be higher in value, to reduce current through the divider.
Try 2K and 1K5 instead and a 0.1uF capacitor from A6 to gnd.

A hint: When you draw your circuit diagrams, try and have gnd as line along the bottom of the diagram and positive along the top.
Then connect everything up to or down to those wires.
Input usually on the left and output on the right, so your diag will have 7.2V supply, switch and potential divider on the left and the BJT, MOSFET and DC-DC converter with motor on the right with the BLE in the middle.
Your first attempt is good, keeping components spaced and using proper symbols, practice will hone your skill. :+1:

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

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I hereby release random internet stranger raschemmel from all liability stemming from my financial decisions.

Now, may I please spend my money as I see fit?

1 Like
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Under battery, 15 Amps. So far I have only hooked it up with a DC power supply, so pretty high. Based on a previous suggestion, I at least set up OCP at 500ma while I work on this.

I don't see a part number, so no data sheet, but this is the motor I'm currently trying
https://www.amazon.com/dp/B0925WDZSH/ref=dp_iou_view_item?ie=UTF8&th=1

ACEIRMC XL6019 5A High Power Current DC to DC Step-up
https://www.amazon.com/gp/product/B082XQC2DS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

I noticed that one, I was losing something like 200ma. Out of curiosity, what is the capacitor for in this case?

Thanks for the tips :slight_smile:

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Hi,

The cap is just to prevent any noise that could make your analog readings vary, its a standard practice to keep the analog signal clean.

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

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LOL
(really not necessary. I was simply pointing out that
if you have no design experience it makes more sense to consult those who do before burning up
boards.
is not very cost effective or productive for that matter. It just results in time and money wasted)

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