Nano + rf + vibration motors

Hi

I'm currently putting together a project, a part of which is controlling a standard coin vibration motor over 433mhz. I'm prototyping this (rather compact) receiver unit with a 5v nano. The problem I'm having is that the coin vibration motors I have are max 3v, but the RF receiver needs 5v to run. The 3.3v output from the nano (I believe) only gives around 50 ma max, but these motors run at around 60 ma and likely have a starting current of probably anything between 85 - 120 ma.

I'll be using this circuit for the motor.

  • Might anyone have any suggestions? Is there an easy solution to step down from 5v to 3.3v?

  • Additionally, would I be better off with a pro-mini for this project?

  • It also needs to be compact, and will need to be battery powered, so I guess I'm looking at using 3 or 4 x AAA batteries?

Any help greatly appreciated.

You will need a regulator that's rated for your needs to go directly from the batteries to 3.3V. Use a schottky diode to drop the voltage down 0.3V after that.

wolframore:
You will need a regulator that's rated for your needs to go directly from the batteries to 3.3V. Use a schottky diode to drop the voltage down 0.3V after that.

Brilliant, thanks. Would it also be a solution to just use the PWM output to the motor at 60% to drop the voltage to 3V? i.e. using

analogWrite( 3 , 153 );

Also, do you think it's ok to use 3 x AAA alkaline cells (4.5v) connected to the 5v pin (27) to power the nano (in this setup)? Or would it be safer to use 4 x AAA on the VIN, so I can run the rf receiver off pin 27?

try it... the 328 needs 5V to do 16MHz... 4.5V will sag and possibly cause issues... the regulator datasheet really need to be above 6V as there's a 1V dropout. Again your battery will sag as it discharges. It should work but won't give steady 5V after a while.

What works and what's recommended are two different things. It might work but it won't work well and you might not be able to utilize all of the power in the batteries at your proposal.

wolframore:
try it... the 328 needs 5V to do 16MHz... 4.5V will sag and possibly cause issues... the regulator datasheet really need to be above 6V as there's a 1V dropout. Again your battery will sag as it discharges. It should work but won't give steady 5V after a while.

What works and what's recommended are two different things. It might work but it won't work well and you might not be able to utilize all of the power in the batteries at your proposal.

Great, thanks. What do you think about the PWM solution - have I perhaps misunderstood how PWM works re: voltage?

PWM give average voltage... might be safe... might not. If you pulsed 6V you would be getting spike of 6V to that motor rated for 3V... again if you are going to do something beyond what the datasheet recommends the risk is yours. I would go with it's own power source. You can pulse that all you want.

Here's an example where they are pulsing 5V... again try it:
3V vibration motor PWM control

wolframore:
PWM give average voltage... might be safe... might not. If you pulsed 6V you would be getting spike of 6V to that motor rated for 3V... again if you are going to do something beyond what the datasheet recommends the risk is yours. I would go with it's own power source. You can pulse that all you want.

Here's an example where they are pulsing 5V... again try it:
3V vibration motor PWM control

That's awesome, thanks! Will try both approaches, but yes, definitely more a fan of risk-free solutions!