Power questions - Arduino

Using Arduino General Electronics
1

Hello everyone,
I'm trying to test an Arduino system in low power mode, to make it run for the longest time.
I think I lack basic knowledge in electronic to continue this. I'd like to have your opinion on some questions I have :slight_smile: (sorry if it's stupid questions...)

I use an Arduino Pro Mini to collect distance data every minute from a sensor HCSR04 and send it with LoRa system (RN2483). Then turn it off, to save battery.

1. 5 Volts and 3.3 Volts
In the datasheet, it is said that the sensor HCSR can be powered in 3.3V & 5V, but my experience is that it doesn't work when on 3.3V.

So I took an Arduino Pro Mini 5V, plug the sensor, with a transistor to turn the HCSR04 off when not needed (to save battery). It works good!

But the LoRa RN2483 needs 3.3V -> problems to power it, and to communicate in RX/TX.
I then saw that it can work using 1kOhm resistors, as seen here. I tried it, and it works.

I guess it's a bit dirty to do this, so I'd like to have your opinion on this... I have also shift level converters, but i would need a 5V and 3.3V source right?

2. How to power it ?
I tried then to power the whole thing "just to see" with 3x1.5V = 4.5V Alkaline (VARTA industrial) in the RAW pin. after some time (1h), the HCSR04 doesn't work.

Does it means that the voltage goes to low to make the HCSR04 work properly? So if i put for exemple 6x1.5V = 9V, the regulator transform it in 5V as long as the voltage is upper 5V, and when it's lower than ~5V it would stop to work?

In that case, i would need to have a battery at 12V (the max for arduino) with a max of "A.h" to make it last longer... Right?

3. The role of the regulator
This is a general question, but how does the regulator convert 12V into 5V? by modifying the intensity ? By heat ? I guess I would need a good tutorial to understand more about intensity and Voltage, and how they are linked... If someone have that :wink:

4. Voltmeter
I connected another 'Voltemeter'-Arduino to my system, GND to GND and A0 to the RAW pin of my system. I try to read the voltage of my battery. Is it the good way ? If I do this, does my 'Voltemeter' consumes power from my system ?

I'm sorry for the multiple questions, and hope it's clear enough... !

Regards,
Simon

2

Of the first two datasheets for the HCSR04 if definitely says 5V only, which makes sense as it has to ping
a powerful sound wave out and needs brief high power pulses. Arduno boards can provide 3.3V out for
the LoRa module - check the current spec though.

There are two types of regulator, linear whic burn off the excess voltage as heat, and switch-mode (buck
converters) which don't, but generate switching noise. The on-board Arduino regulators are typically
linear, including the Pro Mini. The one on the Pro Mini is very small and will easily cutout if too much
current/voltage is put through/across it.

Perhaps use a 2S LiPo pack, 7.4V is enough for the regulator, but not too much.

Never connect any Arduino pin to the battery directly, that will destroy the chip. Any voltage more than
a fraction of a volt outside the GND--Vcc range will trash an IC.

You need a voltage divider to measure voltages above Vcc.

3

Wow lots of questions, that’s a good thing but lots to try to answer

  1. HCRS 04 is only 5V datasheet the other datasheet I found says the same.
    Never tried current limit for level converting, there are simple methods out there especially since it’s single side transmit. I would be concerned about voltage on this also. Not sure how safe that method is in long run.

  2. If you’re using battery to power it sounds like you need a min of about 4.5V to work. You could use 12v or whatever works for you. See next.

  3. The regulator on Arduino are linear which means it’s not very efficient and converts excess voltage (and current) into heat. To save power it would be good to use a DC-DC buck converter. Linear regulators are less than 50% efficiency in best case but if you’re using 12V efficiency could be low as 30% or less. Buck converters can be between 80-90% (higher or lower) based on load.

  4. If you mean by raw being the actual battery anode, it will work as long as it’s under 5v. If you put in a higher battery it can damage A0. In this case you would need a voltage divider. There are some challenges to getting accurate reading but perhaps you just need to be close.

Anything we do consumes power. Your battery reading will consume power. There are ways to reduce the amount of power you use for this. One way might be to switch off this connection.... etc.