# ATTiny85 Low Voltage on Output Pins **URL:** \ **Category:** 3rd Party Boards\ **Created:** [October 20, 2024, 3:28pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381 "2024-10-20T15:28:45Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![karlsangree](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/karlsangree/32/1099124_2.png) [@karlsangree](https://forum.arduino.cc/u/karlsangree)\ **Post date:** [October 20, 2024, 3:28pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/1 "2024-10-20T15:28:45Z")
I just got done pulling my hair out over a low pin voltage issue. I had an RGB led on pins PB0, PB1, and PB2 and a pushbutton on pin PB4. All my sketch (created and uploaded in the Arduino IDE) did was turn on the leds when the button was pressed. The chip was powered with a 5V bench supply. Nothing was happening, and when I measured the voltage at the pins, I was only reading about 1.5 volts. With the leds having a forward bias of ~2V, it's no wonder they were not lighting. I ended up using a new ATTiny85 chip and now all is right with the world and the pins are sitting near ~5V. I had done some mess-around programming using direct writes to the registers instead of the usual pinMode, digitalWrite, ect. I was also messing around with putting the chip to sleep. Is there anything I could have screwed up programmatically to cause the low pin voltage or was this a hardware problem caused by either a defective chip or over-programming. I've burned the chip at least 20-25 times. Unfortunately, in my frustration I deleted everything so I could start from scratch and only have the bare bones blink sketch which is working perfectly with the new Tiny85. ---
**Author:** ![sterretje](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/sterretje/32/391294_2.png) [@sterretje](https://forum.arduino.cc/u/sterretje)\ **Post date:** [October 20, 2024, 4:18pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/2 "2024-10-20T16:18:13Z")
You don't mention series resistors for the LEDs. ---
**Author:** ![kmin](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kmin/32/1147370_2.png) [@kmin](https://forum.arduino.cc/u/kmin)\ **Post date:** [October 20, 2024, 4:39pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/3 "2024-10-20T16:39:35Z")
> [@karlsangree](#): > > Is there anything I could have screwed up programmatically to cause the low pin voltage Maybe some form of "PWM" could. > [@karlsangree](#): > > was this a hardware problem caused by either a defective chip or over-programming. I've burned the chip at least 20-25 times. Doesn't sound a lot... ..or was it your error abusing voltage/current limits of your MCU? ---
**Author:** ![karlsangree](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/karlsangree/32/1099124_2.png) [@karlsangree](https://forum.arduino.cc/u/karlsangree)\ **Post date:** [October 20, 2024, 4:49pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/5 "2024-10-20T16:49:17Z")
> [@kmin](#): > > ..or was it your error abusing voltage/current limits of your MCU? It could have been, although I thought I was being careful. I had current limiting resistors (150 Ω) on the LEDs which, given the voltage should have held the current to 20mA. ---
**Author:** ![karlsangree](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/karlsangree/32/1099124_2.png) [@karlsangree](https://forum.arduino.cc/u/karlsangree)\ **Post date:** [October 20, 2024, 4:50pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/6 "2024-10-20T16:50:12Z")
> [@sterretje](#): > > You don't mention series resistors for the LEDs. Yes, I had series resistors to start. 5v supply - 2v forward voltage = 3v / 20 mA = 150Ω. It worked great for a while, and then the pin voltage dropped to 1.5V. ---
**Author:** ![EmilyJane](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/emilyjane/32/821537_2.png) [@EmilyJane](https://forum.arduino.cc/u/EmilyJane)\ **Post date:** [October 20, 2024, 5:14pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/7 "2024-10-20T17:14:15Z")
The data sheet doesn't guarantee I/O current above test conditions of 10mA/5V and limits total I/O current to 60mA but I don't know if exceeding those limits would kill the chip. Maybe a substandard chip. pp161-162 of the data sheet. ---
**Author:** ![kmin](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kmin/32/1147370_2.png) [@kmin](https://forum.arduino.cc/u/kmin)\ **Post date:** [October 20, 2024, 5:18pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/8 "2024-10-20T17:18:13Z")
> [@karlsangree](#): > > It could have been, although I thought I was being careful. Ones in a while it happens to everyone, even if careful... Anyway, I wouldn't be concerned about programming or flashing the chip, just go on and if something like that ever happens again, examine the setup better. ---
**Author:** ![JCA34F](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jca34f/32/340148_2.png) [@JCA34F](https://forum.arduino.cc/u/JCA34F)\ **Post date:** [October 20, 2024, 5:22pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/9 "2024-10-20T17:22:29Z")
Did you set the pins to: ```arduino pinMode(pin,OUTPUT); ``` ? ---
**Author:** ![JCA34F](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jca34f/32/340148_2.png) [@JCA34F](https://forum.arduino.cc/u/JCA34F)\ **Post date:** [October 20, 2024, 5:32pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/10 "2024-10-20T17:32:16Z")
With modern HI brightness LEDs, I would think about 11mA (270Ω) would be too bright to stare at. ---
**Author:** ![karlsangree](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/karlsangree/32/1099124_2.png) [@karlsangree](https://forum.arduino.cc/u/karlsangree)\ **Post date:** [October 20, 2024, 9:05pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/11 "2024-10-20T21:05:55Z")
> [@JCA34F](#): > > Did you set the pins to: Yes. I've been working with Arduinos for years. This is my first foray into direct register writes on a ATTiny85 chip. The hardware/software has been working (constantly for a day now) perfectly with a new chip. My original question was, could I have messed up the chip with direct register writes code. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [April 18, 2025, 9:06pm UTC](https://forum.arduino.cc/t/attiny85-low-voltage-on-output-pins/1313381/12 "2025-04-18T21:06:37Z")
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