low-pass filter

It is a low-pass filter. Because the output is being measured across the capacitor, it allows low-frequency signals to pass through easily while shorting high-frequency signals to ground. If the positions of the resistor and capacitor were swapped (taking the output across the resistor), it would be a high-pass filter. Low Pass Filters email

In hobbyist electronics and practical prototyping (like the Arduino and signal processing projects you are working on), you will generally stick to standard, widely available component values.

Here are the most common practical values used for creating low-pass and high-pass filters:

Common Resistor ($R$) Values

For filtering and timing circuits, resistors typically range between $1\text{ k}\Omega$ and $100\text{ k}\Omega$.

• Going below $1\text{ k}\Omega$ (like your current $180\text{ }\Omega$ or $200\text{ }\Omega$ setup) draws more current from your signal source, which can overload microcontroller pins.

• Going above $1\text{ M}\Omega$ makes the circuit susceptible to stray electrical noise.

Standard breadboard choices:

• $1\text{ k}\Omega$, $4.7\text{ k}\Omega$, $10\text{ k}\Omega$ (Very common for high-frequency filtering/pull-ups)

• $47\text{ k}\Omega$, $100\text{ k}\Omega$ (Common for audio-range filtering and timing delays)

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Common Capacitor ($C$) Values

Capacitors have a massive range, but for filters, they generally fall between $100\text{ pF}$ and $10\text{ }\mu\text{F}$. Your current value of $33\text{ }\mu\text{F}$ is relatively large for a signal filter and is typically an electrolytic type, which has wide tolerances.

Standard breadboard choices:

• Ceramic Caps ($100\text{ pF}$ to $0.1\text{ }\mu\text{F}$): Used for filtering out high-frequency noise, radio interference, or debouncing switches. $0.1\text{ }\mu\text{F}$ ($104$) is the single most common decoupling value.

• Film or Electrolytic Caps ($1\text{ }\mu\text{F}$ to $10\text{ }\mu\text{F}$): Used for audio-frequency filters (bass/treble cuts) and low-frequency timing.

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The "Sweet Spot" Rule of Thumb

When designing a quick filter on a breadboard, it is usually easiest to choose your capacitor first based on what you have in your parts kit, and then calculate or dial in the resistor to hit your target frequency.

A very common default pairing for a basic audio or signal filter is a $10\text{ k}\Omega$ resistor paired with a $0.1\text{ }\mu\text{F}$ capacitor, which yields a cutoff frequency of right around $160\text{ Hz}$.

100k

100p

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