Onboard supply voltage - a bit of a conundrum

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MaxZ
Posts: 143
Joined: 31 Jan 2019, 11:48
Location: Boskoop, Netherlands

Onboard supply voltage - a bit of a conundrum

Post by MaxZ » 08 Jul 2019, 10:37

I am looking for advice here. When I am using arduino boards to drive servo's in a model, I tap the supply from the BEC in the ESC, which normally delivers around 5V. Should I hook this up directly to the 5V connection on the board, or would it be safer to hook it up to the V-in of the regulator?
The minimum supply voltage of the ATtiny85 chip for instance is specified as 2.7V, so the voltage drop over the regulator should not be a problem. However, the PWM signal to the servos will probably drop by the same amount, and this could be a problem. I will supply power to the servos directly from the bec, no question there.
Any thoughts?

Cheers,
Max.

Martin
Posts: 311
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Re: Onboard supply voltage - a bit of a conundrum

Post by Martin » 08 Jul 2019, 12:57

I think you're safer connecting to the V-in pin. The Atmel chips run fine at below 5V, and I've never had a problem supplying the PWM to servos at a lower voltage than their supply rail.

I would check the VCC on the Arduino board when it's being supplied by 5V on V-in to make sure that it's not ridiculously low. It depends on what type of regulator is fitted on the Arduino board - whether it's a low dropout one or not. As long as VCC is at or above 3.3V I don't think you'll have a problem.

If you find that VCC is below 3.3V, then I would check that the output from your BEC is really a maximum of 5V, and if so connect it direct to VCC. The Atmel chip voltage absolute limit on the datasheet is 6V. I've never tried pushing beyond that to discover what the real limit is before the magic smoke appears! :lol:

I suppose if the BEC voltage is a little on the high side - say 5.5V - then you could just feed the Arduino VCC via a diode to drop about 0.3V to 0.7V. An ordinary rectifier diode such as an 1N4001 would be fine.

MaxZ
Posts: 143
Joined: 31 Jan 2019, 11:48
Location: Boskoop, Netherlands

Re: Onboard supply voltage - a bit of a conundrum

Post by MaxZ » 09 Jul 2019, 11:47

Thanks Martin, I'll do the measuring and then decide.

Cheers,
Max.

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