Powering ATtiny85 with 4 AA batteries

Hi,

I'd like to power an ATtiny85 with 4 AA batteries. On the ATtiny85 datasheet (Smart | Connected | Secure | Microchip Technology , page166) I could read that the maximum operating Voltage is 6.0V. The problem is that even though theorically 4 AA batteries should provide 6V, normally this voltage is slightly exceeded. Can this damage the ATtiny85? What are your recommendations?
Thank you in advance

Hi,

You could run rechargeable AA's which output only 1.2V or thereabouts, therefore the total would be 4.8V well within the safe voltage for the ATTiny, alternatively if you have flexibility with the configuration, 2 parrallel pairs in series for a total of 3V you'll still be able to run the ATTiny, and that should last for a very long time too (depending what else you have it running).

I often match up ATTiny85 with power from a single CR2032 3V coin cell and they run for ages.

Is there a reason you're wanting to run with 4x AAs specifically?

Cheers ! Geoff

Can this damage the ATtiny85? What are your recommendations?

Unlikely.

You can try and if you are really concerned, put a small resistor (1k or 10k) to the supply rail and run some simple task on the mcu (like flipping some pins). The resistor there limits the current.

Or you can run it with just 2 - 3 batteries.

jvf1986:
Hi,

I’d like to power an ATtiny85 with 4 AA batteries. On the ATtiny85 datasheet (http://www.atmel.com/Images/doc2586.pdf , page166) I could read that the maximum operating Voltage is 6.0V. The problem is that even though theorically 4 AA batteries should provide 6V, normally this voltage is slightly exceeded. Can this damage the ATtiny85? What are your recommendations?
Thank you in advance

Batteries don’t provide 1.5V. That’s a complete myth. The actual voltage varies over time like this:

For most of their life they only put out 1.1 to 1.3V (that’s about 5V for four batteries, not 6V as you’d expect…)

So… four new batteries will put out about 6.5V for a short while - too much for the AVR chip.

The chip will run happily down to three volts so three batteries would be much better. What are you going to connect? Will that work with three?

dhenry:
Unlikely.

Bullshit.

  1. Electrical Characteristics
    21.1 Absolute Maximum Ratings*

*NOTICE: Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

You can put a 1N4004 diode in series with the batteries, it will drop to 6V to 5.3 and keep things safe.

I wasn’t sure if the OP must run the project on 5 volts. I have a current hobby project
based on the Tiny85 that is using a 3.3 volt regulator. The Atmel data sheet indicates the
Tiny85 can operate at less than 2 VDC.

I attempted to insert a PNG snapshot but don’t know how to do that yet here at this forum.

Click "Additional Options" below, then browse to your computer location and attach the file.

Thanks for the info on inserting graphic content, I will give it a test:

Well, I did the Additional options to insert a graphics (test file) , but do not see it in the preview.
I will go ahead and post and see what happens.

You can put a 1N4004 diode in series with the batteries, it will drop to 6V to 5.3 and keep things safe.

A diode's forward voltage drop is a function of the current going through it. If that's what you have to do, put a electrolytic capacitor on the diode's cathode.

dhenry:
A diode's forward voltage drop is a function of the current going through it. If that's what you have to do, put a electrolytic capacitor on the diode's cathode.

Can you please elaborate on why to put an electrolyte capacitor on the diode's cathode ?

What he is pointing out is that the diode impairs the regulation of the supply - in this case, the battery, so you need a decent decoupling capacitor - from VCC to ground - after the diode.

In fact, there should always be a capacitor - 47 µF or so as well as the 0.1 µF - across the MCU including when using any sort of batteries.

Paul__B:
What he is pointing out is that the diode impairs the regulation of the supply - in this case, the battery, so you need a decent decoupling capacitor - from VCC to ground - after the diode.

In fact, there should always be a capacitor - 47 µF or so as well as the 0.1 µF - across the MCU including when using any sort of batteries.

Thanks for pointing out that the diode would impair the regulation of the supply. With tiny mA current the diode would have a linear behavior where delta I in current consumption would translate to delta V in voltage drop. This behavior is undesired since the uP is expecting a constant voltage behavior instead.

With tiny mA current the diode would have a linear behavior where delta I in current consumption would translate to delta V in voltage drop. This behavior is undesired since the uP is expecting a constant voltage behavior instead.

Nothing in the above statement is correct.

Diodes have an exponential current/voltage relationship.

The uP does not expect constant voltage, and as stated, can run from about 1.8 - 5.5 V.

jremington:
Nothing in the above statement is correct.

Diodes have an exponential current/voltage relationship.

The uP does not expect constant voltage, and as stated, can run from about 1.8 - 5.5 V.

The diode has fairly linear relationship from 0 to about 0.3V. Only > 0.4+ it behaves exponentially.
If the uP or its regulator is fine with whatever however voltage it is being fed then I don't know the point of using more capacitor that is supposedly keeps the diode from imparing the uP operation.

The diode has fairly linear relationship from 0 to about 0.3V. Only > 0.4+ it behaves exponentially.

Where do you get these silly ideas?

lol. some really bizarre advice being doled out here. im not sure what makes less sense, 1k-10k series resistor, BIG supply caps, or that fuss over the diode which is really an excellent way to drop voltage. fortunately there are a couple guys here with feet on the ground. unfortunately noobs cant always tell whos who.

personally i doubt that for hobby use 4 new alkaline would be a problem. it dont make a lot of sense though. current will be extremely high, non-standard voltage for interfacing, and little advantage over 3 cells, 4 nimh, or a single lithium. powering off a single cell (regardless of type) with cheepo ebay 50 cent boost module is another way to guarantee exactly 5v.

It is important not to confuse the ability of the MCU to operate over a wide supply voltage range with the importance of supply bypassing - which means both "bulk" bypassing (47 µF is what is used in the UNO) and high frequency bypassing (0.1 µF being the commonly used value).

Reliable operation is almost always dependent (perhaps not when merely flashing LEDs) on the supply voltage not suddenly and transiently changing.

"Big" supply capacitors - if this is what you mean - are simply part of proper engineering design.

maybe for extremely noisy supplies like usb power, dirty switchers, or driven devices like servo, relay, or motor. in these cases an inductance or small series resistance is also recommended. admittedly ive seen it help low current circuits in situations involving flaky battery holders too. in the uno i suspect its more to stop the ldo from singing because according to spec the .1 alone is not up to that task.

however for me .1 does the job in most battery applications and that is the standard advice for hobbyists. of course we are all entitled to our own theories and guidelines and its unlikely to do any harm. except possibly a slight reduction in reliability due to the extra component itself.