Why does my multimeter shows 0 current on Attiny85?

Hi everyone,

I have an attiny85 on a breadboard and a led on pin 2 blinking every 2 seconds.

The multimeter is connected on the VCC pin of the attiny85. When led is ON I can see current flowing on my multimeter.. when led is OFF i see 0 current..
I tried all the "A" settings of the multimeter 10,200m,20m,2000μ.

The multimeter is a cheap lexman pt1000 .

Is it because my multimeter isn't super precise? If yes, what should I buy?

I want to test the sleep modes etc thats why I am trying to check the current flowing while NOT on sleep mode.. if my multimeter isn't precise enough to see the current drawn by the attiny85 when led is off then imagine when on sleep mode!!
any thoughts gents?

You need special equipment and procedures to measure sleep current. The uCurrent GOLD is popular and inexpensive, but is currently out of stock. You can make your own, though.

What does this mean? You need to interrupt a connection to measure current. The ATtiny85 typically draws about 5 mA while running at 8 MHz (with no LEDs or other loads being powered).

The multimeter is connected on the VCC pin of the attiny85

Meters use resistors to pass current through and measure the voltage drop to determine current. If that value is to high you will not get your system to work as it does not have enough voltage. Cheat and do the same thing with a low value resistor, start maybe with 100 ohm and go from there. You can calculate the current using ohm's law. Be careful you have enough voltage left for your micro.

I did interrupt the vcc. I connected the multimeter on voltage and the other side in the vcc pin of attiny85. I can see current value when led is on but 0 when its off :confused:

You can buy sensitive moving coil meters from eBay - 100mico amp or even less .

Fix this with a normally closed push button wired across it .
Use this to measure your sleep current - when you think it is sleeping press the button and measure the current .
The button stops higher currents passing through the meter and burning it out
The meter I calibrated with a known resistor in series with it and my DVM.


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There is an easy solution.

Short across the meter connections with a wire or switch and put the meter on a uA range, 200uA is typical.

When the processor goes to sleep remove the short across the meter and as if by magic you will be able to measure sleep currents in the less than 200uA range.

I have a uCurrent Gold, and never use it, the meter short method is just plain easier.

Details on how to use a standard multimeter to accuratly measure low currents are described here;

Measuring Low Currents

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As my alternative ... the full picture :

My full install is this - 100mA meter in series with a 100micro amp meter ( on right) which has the shorting link via push button .

I can power stuff through this and know when the current is low enough to check the micro amps on the second meter.
Bought the used meters cheap of ebay ! ( not really kV ...)

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To use the 10A setting on the multimeter, the red lead is usually put in a different socket from the other ranges.
To distinguish between a usage problem and a failure of the multimeter, simply use a 5v power source and put resistors in series with the meter. A 5k resistor should show a reading of 1mA. A 5megohm will show 1uA etc.
An ATtiny85 in sleep mode will consume between 1uA and 1mA depending on the selected sleep mode, the peripherals still running, the state of the pins etc. etc.
Even a cheap multimeter is good enough for the sleep mode itself because the current consumption is constant. However, that is not the same as overall power consumption when the device is sleeping for some of the time and actively doing things the rest of the time, which is more useful for estimating battery life etc.

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