# ATtiny85: Power consumption vs clock speed

Short and simple: What is the power consumption for an ATtiny85 running at 1 MHz and 8 MHz using the internal clock? Not using any sleep modes.

I have googled a lot and can't find any info on this. I ask because I want to know if it is worth using 1 MHz to increase battery life.

• The datasheet is the 1st place to look for things like this – Russell McMahon Aug 6 '15 at 2:54
• I actually did look in the datasheet. But is very long (234 pages) so I searched for strings like "power consumption" etc without luck. If I had just searched for "current" instead I would have found it! – marlar Aug 6 '15 at 8:31

The datasheet shows that current decreases at lower frequencies. Around 1 mA at 1 MHz running at 5 V. More like 5 mA at 8 MHz running at 5 V.

You can save quite a bit by using lower voltages as well, as you can see. For really big savings use a sleep mode. Read about Power saving techniques for microprocessors.

To amplify on my remarks, you should be able to get 200 nA consumption at 3.5 V in sleep mode with no watchdog timer. That will still respond to interrupts, such as closing a switch.

If you need to do things periodically you can enable the watchdog, and then get around 5 µA consumption at 3.5 V.

This is so much less current than the 1 mA mentioned above, that it is well worth exploring running in power-down mode, where possible.

• Nick - that page is a very nice resource. Thanks – Russell McMahon Aug 6 '15 at 2:58
• Wow. This answer is brilliant and a perfect example why I love Stackexchange so much. Thanks a million! – marlar Aug 6 '15 at 8:29
• Nice answer. I would just add that, when using sleep modes, the relevant metric for active mode consumption is not the current (consumed charge per unit time) but the consumed charge per clock cycle. Thus, it seems that running at 8 MHz is more efficient (5 mA / 8 MHz = 0.625 nC/cycle) than running at 1 MHz (1 mA / 1 MHz = 1 nC/cycle). – Edgar Bonet Aug 6 '15 at 8:37
• @marlar, if the thing that the Attiny controls uses 12v, then you should first and foremost look at the power consumption of this device - it's no good saving 2 or 4 mA, if you are running something that draws 2 amps. – AMADANON Inc. Aug 6 '15 at 21:34
• @AMADANONInc.: you are of course right. But the controlled components are dormant most of the time and use no power except when attiny think it's time to call to action. Apart from that, there is certainly also a learning element here. I really want to investigate low-power mode. – marlar Aug 7 '15 at 6:29