Power management help

Hi everyone,

I'm pretty new to custom PCB's, but learning.

I have already made a control unit off a Nano that controls a 12v solenoid with a TIP120 (flyback diode included) as well as some ancillary components like a float switch, a push button rotary encoder and an 2004 LCD that is working well.

I'm now trying to prototype using a Nano IoT 33 instead, so I can get it connected up to a MQQT platform (Cayenne) and need some help managing different power supplies. (3.3v / 5v / 12v)

I haven't mapped out the schematics yet in Fritzing yet, as I want to make sure I'm going down the right path first.

I have read that the 5V on the Nano IoT33 isn't the best, so a separate voltage converter is better to get 5v. I was planning to have a AMS1117 (capacitors includes as per the data sheet) for steady 5v supply.

The specs on the devices I am working with are the following

LCD 2004 - 5v for LCD - A4/A5 for SDA/SLA
Float switch - Effectively a push button
Flow meter is 5v -24v NPN output
Rotary encoder - says 5v on package, but I've heard people say they work fine on 3v3. If anyone can confirm that would be great.

My plan was to have 12v input supplying the solenoid, VIN on the IoT33 as well as supply power to the AMS1117.

Then the 5v power supply can supply voltage to the LCD, flow meter which I can use voltage dividers on the output to drop it to 3.3v.

The float switch and the rotary encoder can run off the 3.3v. If the rotary encoder doesn't like 3.3v then I can use it on the 5v supply and voltage dividers to drop down to 3.3v on pins, but that's easy to test on a breadboard.

Like I said I'm pretty new to all this so just wanted to check if I'm going down the right path or am I over complicating it out of my own naivety.

The Arduino Nano 33 IoT is a 3.3V board. The board is powered by 5V from the USB connection, which is then stepped down to 3.3V with the MPM3610. The issue you may be referring to is likely the 3.3V. It is a bit noisy. Whether this is acceptable depends on your application.

Should work, but doesn't give much headroom for additional current draw if Vin=12V. Better use a buck step down converter than a linear regulator. You could use a buck DC-DC to get down to e.g. 5V and then a linear regulator for 5V to 3.3V. This gives a clean 3.3V for the IoT33 and auxiliary sensors etc. while also reducing most of the power dissipation.

Your rotary encoder will work at any voltage up to probably 12V or so. Don't worry about it.

Assuming your 2004 display likes to run at 5V and your IoT33 is 3.3V, have you thought about how you'll interface them?

Fritzing for schematics? Yuck.

Ok great, the buck converters I've see are all complete circuit boards. Is there a pcb mountable buck converter or is it a matter of understanding the components and building it into the PCB?

Well not for schematics but to plan it out and to make the PCB. I'm learning Kicad, but I find Fritzing easy to get my head around in the interim.

Any ideas on how to the flow meter will work with voltage dividers? This is the data sheet if that helps https://docs.rs-online.com/3649/0900766b815eefbb.pdf

If you desire, yes. The components are easy to get in most places.
Or you could just get a ready-made board and mount that onto a PCB of your own design.

Good! Then maybe quit Fritzing cold turkey? All the time you spend on Fritzing now, you don't spend on gaining experience with KiCad. With KiCad, you're going places. With Fritzing, you'll be stuck in teenage-hobby space forever.

Didn't read the datasheet you linked to, but if its maximum output voltage is 24V, just use a 1:4 voltage divider ratio. 22k:100k would already work. That would give around 4.37V max for 24V from the sensor. For protection you could always throw in two Schottky diodes (or a single BAT54S); one with the anode to GND and cathode to your Arduino input pin, one with anode to the Arduino input pin and the cathode to Arduino Vdd.


hahah, thanks for the pep talk, appreciate the nudge and will take the plunge.

The flow meter has a voltage range of 5v-24v so considering ill be powering off 12v wall wart and using a buck converter to 5v I could use either of those to power the sensor but adding 24v would add more complexity. What I get what you said is a voltage divider will be fine. Using a LLC seemed overkill for this application.

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