The Arduino Uno has Schmitt Triggers on its input pins, and you can measure the logic and hysteresis levels with your Uno's analogRead(). The Schmitt Trigger shown on this schematic translates the analog readings on the pin to digital levels with hysteresis: [image] If you connect a potentiomete…

In the mega328 data sheet the Table 28.2 (page 258) lists the values for Vil and Vih. They are dependent on Vcc. Vil is for a voltage that is dropping. When the voltage drops through Vil the input will switch from HIGH to LOW. Conversely, with a rising voltage the input will switch from LOW to H…

[image] Thanks, I was interested in seeing the behavior in the unspecified space between "the highest value where the pin is guaranteed to be read as low" and "the lowest value where the pin is guaranteed to read as high"

If the voltage at the digital input is between 0.3 * Vcc and 0.6 * Vcc at reset the state of the input is indeterminate. The same as floating until the input is set to a known state by raising or lowering the voltage passed the threshold. Is that what you mean?

If the voltage is HIGH to start with, it will remain so until the voltage drops below 0.3 * Vcc. And if it starts LOW it will re.ain so till the voltage rises past Vcc * 0.6.

I think the spec is saying the opposite -- one should design a reliable digital sensor to produce voltages outside the {0.3*Vcc, 0.6*Vcc} range to be reliably read, because it is unreliable in between. As measured here: [image] DaveX: Dig:0 Analog:446 Diff:70 Volts:2.180 dVolts:-0.342 Dig:1 An…

[image] DaveX: because I wanted to hook up an IR photodiode and bias it so I could read it as a digital input. Yes it’s another chip but a LM339 might be the way to proceed. :thinking: [IMG_1099] 4 circuits in one chip :slight_smile:

[image] DaveX: one should design a reliable digital sensor to produce voltages outside the {0.3*Vcc, 0.6*Vcc} range to be reliably read, because it is unreliable in between. I agree with that. If what I wrote was interpreted differently, I apologize. The above is why there are pullup and pu…

I was trying to mimic the low-budget hacks in: [image] from PIC project DC motor like crystal clockwork! PIC project, xtal locked DC motor, DC motor crystal clockwork ...but using some stuff from my junk box. I thought if his PIC's Schmitt triggers work…

I think what I was perceiving from your words was that the hysteresis behavior is specified as Vil and Vih, while I was more interested in the behavior the schmitt trigger per these graphs from that datasheet: [image]

[image] DaveX: ... if the voltage is HIGH to start with, it toggled LOW when the voltage dropped below 2.18/5=0.43 * VCC, and when LOW, it toggled to HIGH when the voltage rose past 2.527/5 = 0.51*VCC. Your values are really close to what shows on the charts on page 272 ... if you zoom in at …

Hysteresis of Arduino digital inputs, measurement of

Note to self:

IR photo detector wise, these were good:

https://www.teamwavelength.com/photodiode-basics/

Additionally, the Wokwi simulator does not do Schmitt triggers to transform analog signals into digital signals.

Here is a Wokwi demonstration of a Schmitt Trigger using a Wokwi custom chip:

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Hysteresis of Arduino digital inputs, measurement of

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