Lay user (artist) in need of basic help with attiny85

I have used the instructions on High-Low Tech Group for programming at attiny85 using my arduino uno. After some hoops (read downloading the latest versions of everything, and using the 1mhz board) I was able to get the tiny to accept the blink program.

However, when I run the chip from my 9v battery the LOW setting still leaves the light on. It’s dimmer than the HIGH setting on the output, but definately not off. I’m doing this as an art project, and maybe bit off more than I could chew. I took electronics… like 15 years ago, and have only been playing with this stuff for about 2 days.

Anyone want to give me a nudge in the right direction? Why does the blink not turn off when powered on my 9v?

This video is where I got my starting instructions (before I downloaded latest everything) But it gives you an idea what I’m trying to accomplish.

sephatine: However, when I run the chip from my 9v battery...

Directly connected to the processor?

Connected to the attiny85.

I believe that the upper limit is 5.5V Dc for the Tiny 85…
From the data sheet: Operating Voltage
– 1.8 - 5.5V for ATtiny25V/45V/85V
– 2.7 - 5.5V for ATtiny25/45/85


You're right. I just tried it with 3AA batteries (4.5v?) and it still acted the same. The light wasn't as bright, but it still never went to an 'off' state.

Likely the chip went south... Got another?


I have a sleeve of ten of them. I just tried with a new one and it's still a no go. With the lower voltage the light is much dimmer as well, and it's harder to see the cycling between bright and dimmer. It just feels like it's dimly on constantly now.

I also tried moving the output pin to pin 0 rather than pin 3. It gave me the same results.

Is the chip properly wired? Pin 8 is Vcc and pin 4 is ground.. Since you posted neither code or schematic and my crystal ball became so myopic that I had to sent it to Hogwarts for repair.. That's all I can help with...


For the LED to work correctly between the on & off states, the Attiny85 should deliver approximately 20 milliAmps of current. Using 4.5 Volts minus the CMOS voltage drop estimated at 0.5 Volts, youneed to limit current with 4 Volts @ 0.020 Amps... Or, a resistor value in Ohms of 4/0.02 = 200 Ohms.

Values lower than 200 increase brightness but also increase current. You are safe to around 40mA Total of current on the Output pin of the t85 but i have no idea about your LED-check the data worst-case is 100 Ohm at room temperature. If the uC or resistor or LED becomes warm, things can go into thermal runaway and permanent damage could occur.


ATtiny will drive (common) LEDs without resistors without problems, either LOW or HIGH - not tried though with high power ones, also not tried > +5V. ;) 7 segments are brighter (and way nicer) without resistors, especially big ones. My huge 7 segment (1.73") is pretty warm, but the chip is not.

If not too late to you, looks that you are PULLING down (or up) a LED fed by a resistor, or more precisely, you did not setup the pin driving the LED as OUTPUT in your sketch, so it is always fed (never turns totally OFF).

1) Connect all unused ATTINY pins to a negative voltage of the battery using 470 0hm resistors. See if that works. If not, continue as below:

2) Plug ceramic (do not use electrolytic) capacitor's one leg to pin 8 (+ 5V positive voltage input) and the other leg to pin 4 (GND - negative voltage). Use round ceramic capacitor marked 104 and 25 volts (higher or lower voltage say 16V is OK). If that works, you probably don't need the step 1 above.

3) Following youtube connect negative leg of the LED to negative voltage as shown and use 470 Ohm (330 Ohms or little lower will be OK if you don't have 470) resistor. Negative leg of the LED is usually the shorter one.

If you can not determine which one is supposed to be connected to negative, do the following: Connect one leg of a resistor to the positive end of the battery then connect the other leg of resistor to one of the legs of the LED. Connect the other LED's leg to negative terminal of the battery. The LED should light up. If it doesn't, turn it around. The LED conduct current in only one direction. Don't try to do the test without resistor!