Help - Pro Mini keeps resetting

Hi there,

I’m building a low power node with a Pro Mini 3.3V, to measure distance (HC-SR04) and sent it via lora (RFM95 module).

It consists of a mosfet that is switched on and off, regulator, level converter and the US sensor.
It worked perfectly fine on my breadboard but after soldering it to a prototype board, it doesn’t work anymore.

Does anyone see a problem in the schematic? (Sorry for the drawing, I’m a bit limited here, I hope it is clear).

Mosfet (I know, overkill): https://de.aliexpress.com/item/10PCS-IRLB8721-TO220-IRLB8721PBF-TO-220-free-shipping/32714364118.html?spm=a2g0s.9042311.0.0.FjZdIJ
Vreg: https://de.aliexpress.com/item/2pcs-DC-DC-Power-Supply-Converter-Step-Up-Boost-Module-1A-3V-to-5V/32598574742.html?spm=a2g0s.9042311.0.0.IFPbYZ
Lvl Converter: https://de.aliexpress.com/item/Free-shipping-1pcs-4-channel-IIC-I2C-Logic-Level-Converter-Bi-Directional-Module-5V-to-3/32670479389.html?spm=a2g0s.9042311.0.0.OAwsE9

I have verified all the connections.

Right now it seems to reset all the time (2nd LED blinking on the arduino).
The regulator switches on and off with 1hz, the voltage between I+ and I- changes between 1.0V and 2.4V
If I connect GND to the regulator directly, bridging the Mosfet, it works fine.

Any idea?

Good attempt on the schematic. But it's better if you use standard symbols instead of a picture of the device. Or if you do, please label the pins so that we can see what is S, D and G on the MOSFET without having to find and read the datasheet. (The pins aren't always in the same order on every manufacturer's MOSFET.)

Your description told us what the components are and what happens when you switch it on. But what was supposed to happen? What did you expect this circuit to do?

Without looking up the MOSFET pins, I'm taking a guess here. But it kind of looks like you're using pin 7 on the Arduino to control the MOSFET to connect the regulator's ground to the Arduino's ground. That makes no sense. If the Arduino is not grounded to the rest of the circuit, how does it control the rest of the circuit? If you let the regulator float above the Arduino's ground potential then there could be a very large voltage applied to the Arduino's pins.

Try to re-draw the schematic. Use ground symbols so that you don't have to have a ground line snaking its way around the drawing.

Even if you can't get the schematic into symbols, can you:

Draw

  • the powersupply, trying to make the drawing match the actual circuit connections. (i.e. if the powersupply ground first connects to the pro mini gnd then draw it that way).
  • Provide the PN for the Mosfet

Thank you for the answers - I know that the drawing is not a proper schematic, I’m just starting out with all this so I’m not familiar with all the terms and symbol.

I found a similar approach on the internet so I tried to reproduce it - and it seemed to work on the breadboard as mentioned. I’m switching Pin 7 to HIGH during sleep so I don’t lose current through it if GND is disconnected - I’m not sure if this is a good thing to do though, right.

@MorganS you are correct I want to switch on/off the regulator through the mosfet in order to save power during sleep. Therefore pin 7 is supposed to switch on/off GND.

I’m not at home now so i cannot redraw, but I can try to answer the questions if I understand correctly:

GND/VCC of the power supply is connected on the arduinos VCC/GND pins in the right side of the picture.
The mosfet pins in the order on the picture are GDS, here is a datasheet:

As mentioned I’m doing this for the first time so I’m probably making a lot of mistakes.

No need to be sorry about the drawing, we all start somewhere. For drawing schematics I find TinyCAD easy and intuitive. It however has no ability to design circuit boards so many don’t use it for that reason.

Given what you’ve told us I would try the attached.

Ckt Mod.jpg

Good luck

Thanks a lot JohnRob! I will try that.

I came across this page as well:

He does it similar, but uses a npn transistor - would that be better?
I have some bc548 transistors here.

@JohnRob, I have added it as you suggested, but it still keeps resetting.

The sketch I'm using is here:

The Arduino keeps resetting when I switch on the regulator pin (Line 119).
If I disconnect VCC from the regulator, the sketch works fine (it just sends 0) - so the RFM95 part can be ignored I think.

It was working fine on my breadboard. I had to set trigPin to HIGH to not lose current through that pin when GND was disconnected through the mosfet.

Does anyone of you have an idea what could cause the resets now?

It's working!

I have now tested this with the BC548 Transistor and a 1k base resistor - it's working without problems.
Does anyone know why this didn't work with a Mosfet? I tried this setup 2 times and it always
worked on a breadboard, but not when being soldered together.

The current consumption during sleep is now 0.78ua.

I also wondered if I could just use a regulator that can be shut down through a pin directly, I had some of these lying around: https://www.pololu.com/file/0J794/tps6120x-datasheet.pdf

However, when testing it on a breadboard it consumes 35ua in sleep mode - I thought it would go down to almost 0. So the first option using a transistor seems better.

Read the information on the Pololu page. There's a pullup resistor inside the regulator which is the main cause of idle power consumption. If you change it to a higher value like 100K you will make a big difference to the power consumption. If you're actively driving it high with the Arduino, then remove the pullup altogether.

If your project works on the breadboard and not when soldered, then you have not copied the circuit exactly. Try to draw a schematic of each version from scratch. Then compare the schematics. It could be something simple like wiring one component backwards.

Thanks, I will have a look at the Pololu setup.

As for the circuit, I'm 100% sure it is the exact same - I did it twice to avoid any bad joints or anything that could be different, and had 2 colleagues check it.