I'm using a ATtiny84 and with three 74HCT595 serial to parallel converters to drive 24 LEDs. Every thing works fine, but when I try to light up more than 10 LEDs at the same time, the ATtiny84 program resets. I'm thinking a dip in voltage related to high load it causing this.

I've tried running it via a iPhone charger, PC USB but still the same issue. If I use the Arduino Uno to drive the LED's instead of the ATtiny84 it all works fine.

Any ideas on how to get around this? Do I need to add a capacitor somewhere or do I have to switch off some brown out voltage thing in the ATtiny?


I'm trying to make a clock. Two rings of 12 LEDs. The three 74HCT595 are chained using the overflow pin connected to the input of the next one. The 74HCT595 has 8 outputs so I need 3 of them for 24 LED's. The 3 digital pins of the ATtiny84 is used for clock, input and rclk.

Code: https://gist.github.com/anonymous/be75cd17bd5773f0df88

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    \$\begingroup\$ Do you have a capacitor across the voltage input pins of the ATTiny? 100nF are usually enough to block these dips. \$\endgroup\$
    – arne
    Apr 22, 2014 at 12:03
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    \$\begingroup\$ It might be worth adding a schematic or at least more details of the ATtiny84 circuit and how things are connected together. \$\endgroup\$
    – PeterJ
    Apr 22, 2014 at 12:07
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    \$\begingroup\$ @arne At the moment I don't have any caps. Do you mean adding it between the Vcc and the GND of the ATTiny? \$\endgroup\$ Apr 22, 2014 at 12:26
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    \$\begingroup\$ Exactly. Try to keep the physical distance between the pins and the cap as short as possible \$\endgroup\$
    – arne
    Apr 22, 2014 at 12:31
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    \$\begingroup\$ @Arne: Perhaps you or the OP could post the solution (as an answer) so this question won't appear to be unanswered. \$\endgroup\$
    – JYelton
    Apr 22, 2014 at 15:05

1 Answer 1


Repost from the comments section:

Place a decoupling capacitor across the voltage input pins of your ATTiny. 100nF normally suffice to smoothen over short dips in the voltage that result from switching loads, starting motors etc. Try to place the capacitor as (physically) close to the pins as possible. You should have decoupling capacitors for all devices that keep some kind of state, e.g. memory banks, uCs and whatnot.


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