What are the input voltage thresholds for the Raspberry Pi's GPIO pins?
Why Raspberry Pi Stack Exchange recommends it
Raspberry Pi Stack Exchange users cite it as an empirical source for the GPIO logic thresholds when answering questions about sensors, pull-ups and interrupts.
Recommended by 0 people across 0 different months, 2013 to 2016.
What it is
A short 2013 demonstration by Gaven MacDonald that measures the voltage at which a Raspberry Pi GPIO input switches between reading low and high. It reports roughly 1.19 V as the low ceiling and 1.34 V as the high floor on an older Pi.
What people said
Cites Gerben · 2013-10 · Raspberry Pi Stack Exchange · on “How can I get my hardware to generate interrupts?”
I've hooked up an LDR to a pi's GPIO and ground pin directly. I set up the internal pull-up resistor on the broadcom chip. This created essentially a voltage divider, that would make the pin would read low if a led shined on it, and high is not. Since you only need a yes/no answer there is no need to measure the time to charge a cap, just like analog-to-digital converters do. You just need the voltage to be either above or below the tripping point of the GPIO for either state of the led. The tripping point for the gpio seems to be around 1.2v ( [this video] ). So under normal lighting condition the voltage should be above 1.2v. When the led is shining on the LDR, the voltage should be above 1.2v.
Cites Dennis · 2015-04 · Raspberry Pi Stack Exchange · on “GPIO Voltage Thresholds”
It is obvious, that 3,3 V is a HIGH , and 0 V is a LOW at a GPIO input pin. But I am looking for the exact voltage thresholds for the GPIO input pins. I have a Pi B+ and a Pi 2 . Watching this video [this video] (for an older Pi) I get: LOW: 0 - 1.19 V HIGH: 1.34 - 3.30 V Based on this, I connected 1 V to the GPIO input. The GPIO was still a HIGH . This artice [LINK] ( linked here [LINK] ) sais: VIL=0.8V means that if the output is Low it will be <= 0.8V . VIL=1.3V means that if the output is High it will be >= 1.3V These values are coming from the BCM2835, which the Pi until B+ is having [LINK] . I continued reading this article [LINK] : "Normally the voltage threshold is about 1.8V, but it isn'
Cites Aloha · 2016-01 · Raspberry Pi Stack Exchange · on “Raspberry Pi IR Sensor stays HIGH when it shouldn't”
Since you did not specify what kind of IR sensor you're using, I'll assume it's just a regular IR photodiode. Add a pull-up resistor. Pin is high when it detects IR, and low if it doesn't. This will not solve the random HIGH/LOW state, but it makes sure that the value comes from detecting IR and not from random electrical noise. Sources of electrical noise include: Floating pins Fluorescent lighting Basically any unshielded electronics nearby Someone walking into the room (static electricity) Note: Make sure the inside of your box is non-reflective. You will want to seriously bump up the resistor value. The GPIO gets high at around 1.34 volts according to this YouTube experiment [this video] . .