Two Battery Operation

[artswan]

I noticed the Picaxe-18M2 and family advertise 2-battery operation (1.8V min). But, I have used the Picaxe-08M and Picaxe-14M on 3 volts with satisfactory operation for quite some time as their PIC processors show operation down to 2 volts in the datasheets. Is this improper operation? Will it cause harm?

 

[Andrew Cowan]

No chance of harm due to low voltages - just possible unpredictability/unstability. It's not going to damage the chip.

A

 

[hippy]

It's not going to damage the chip.

Probably more correct to say it should not damage the chip and in most cases will not.

Operating outside specification may cause a chip to operate in ways which are not expected and this has the potential to have equally unexpected consequences. If a pin were tied to +V or 0V or directly to an input signal, and a glitch caused that pin to switch as output at the opposite polarity, it could destroy the chip.

It's impossible to quantify in any realistic way and Microchip won't likely say anything but 'operation outside specification is not recommended, may cause permanent damage'. I've not suffered any adverse effects from running below rated voltages.

For program download, it's best to be within recommended voltage to ensure the program does 'stick' in memory.

 

[Minifig666]

That's what the brownout fuse is for isn't it? How can not having enough voltage be harmful, other than from an unpredictable output?

 

[Dippy]

PICs can go a bit daft if the supply droops.
The brownout detect/reset ensures (?) a clean reset when supply droops below threshold and then comes back again and gets over a certain level.
It improves chances of happiness.

 

[BeanieBots]

How can not having enough voltage be harmful, other than from an unpredictable output?

Sounds unbelievable, but some devices REALLY CAN be damaged by too low a voltage. I'm not aware that PICs can suffer such damage but there really are some chips that can.

As Dippy says, at low voltages, the internals can get confused and that can cause internal 'shorts' which can destroy things.

PICs, (or any programmable device) can "forget" their program if programmed at a low voltage. This can happen within minutes, hours, days, months or even years after commissioning which can be very embarrassing.

Many switchers also suffer if input volts are too low. A good design will dissable things if the volts get too low but not all designs are good