Wouldn't it be cool to drive a tiny OLED display, read a color sensor, or even just flash some LEDs directly from your computer?  Sure you can program an Arduino or Trinket to talk to these devices and your computer, but why can't your computer just talk to those devices and sensors itself?  Well, now your computer can talk to devices using the Adafruit FT232H breakout board!

What can the FT232H chip do?  This chip from FTDI is similar to their USB to serial converter chips but adds a 'multi-protocol synchronous serial engine' which allows it to speak many common protocols like SPI, I2C, serial UART, JTAG, and more!  There's even a handful of digital GPIO pins that you can read and write to do things like flash LEDs, read switches or buttons, and more.  The FT232H breakout is like adding a little swiss army knife for serial protocols to your computer!

This chip is powerful and useful to have when you want to use Python (for example) to quickly iterate and test a device that uses I2C, SPI or plain general purpose I/O. There's no firmware to deal with, so you don't have to deal with how to "send data to and from an Arduino which is then sent to and from" an electronic sensor or display or part.

This breakout has an FT232H chip and an EEPROM for onboard configuration. You can read tons more about this chip from FTDI's page and check out our tutorial on how to get started and use our Python code to control the FT232H with Mac/Win/Linux.

This compact board breaks out the pins of a microSD card connector necessary to interface with the card through SPI (Serial Peripheral Interface), and it can be directly integrated into 5 V systems thanks to its on board 3.3 V regulator and level shifting circuits. The 0.1″ pin spacing allows compatibility with standard perfboards, solderless breadboards, and 0.1" connectors.

This carrier board makes it easy to interface a microSD memory card (originally known as TransFlash) with an SPI-capable microcontroller, offering a convenient and inexpensive way to add gigabytes of non-volatile storage to an embedded project. It includes a 3.3 V regulator and level shifters on the four SPI lines, enabling direct integration into 5 V systems, and it provides access to the all of the connections through single 1×9 row of 0.1″-spaced through-holes. A breakaway 0.1″ male header strip is included, which can be soldered in to use the board with breadboards, perfboards, or 0.1″ female connectors, and the board has two mounting holes for #2 or M2 screws.

Breakout Board for microSD Card with 3.3V Regulator and Level Shifters with included header pins.

Breakout Board for microSD Card with 3.3V Regulator and Level Shifters plugged into a breadboard with microSD card (not included) inserted.

For 3.3 V projects, we carry a smaller Breakout Board for MicroSD Card without the 3.3 V regulator, level shifters, and mounting holes. This more basic module (shown in the right picture below) breaks out all of the microSD pins (including the ones used for the SD bus mode interface) rather than just the SPI-interface pins.

Breakout Board for microSD Card with 3.3V Regulator and Level Shifters.

Breakout Board for microSD Card.

For a microSD socket and user-programmable microcontroller on a single board, consider our A-Star 32U4 Prime controllers, which essentially use the same level-shifting circuits to interface a microSD card with an Arduino-compatible ATmega32U4 MCU running at 5 V.

Since many microcontrollers have built-in SPI interfaces, most hobbyist projects communicate with Secure Digital cards in SPI bus mode; this is the only mode supported by this board. (The alternative SD bus mode is proprietary, and a license from the SD Association is required for access to the full specifications.) The pins on this board are labeled according to their functions in SPI mode.

The board is powered by applying 5 V to the VDD pin, and all of the logic pins can be interfaced directly with 5 V systems thanks to integrated level shifters. The output of the integrated 3.3 V regulator can be accessed through the 3V3 pin, and the regulator can be disabled to turn off the microSD card and save power by driving the EN pin low.

By default, the EN and CD (Card Detect) pins are each pulled up to VDD through 100 kΩ resistors. However, there are cuttable traces on the underside of the board to allow you to disconnect each pull-up as desired. These traces are located between pairs of pads (labeled “EN” and “CD” on the board’s silkscreen) that can be bridged with solder to reconnect the pull-up resistor. Alternatively, the neighboring EN and CD pads of these surface-mount jumpers (highlighted in the picture below) can be connected if you want the regulator to automatically be enabled when the microSD card is inserted and disabled when it is removed.

Communicating with a microSD card

The SD Association publishes a set of simplified specifications for SD cards containing information on interfacing with them. However, there are a number of ways to get started without understanding the specifications or writing your own code from scratch, since many microcontroller development platforms provide libraries for communicating with SD cards. For example:

The SD library for Arduino provides functions for accessing files and directories on an SD card. (It also works with Arduino-compatible boards like our A-Star programmable controllers.)

The SD Card File System library for mbed allows similar filesystem access.

Schematic

Breakout Board for Micro SD Card with 3.3V Regulator and Level Shifter schematic diagram.

This schematic is also available as a downloadable pdf (106k pdf).

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Add quadrature encoders to your LP, MP, or HP micro metal gearmotors (extended back shaft version required) with this kit that uses a magnetic disc and hall effect sensors to provide 12 counts per revolution of the motor shaft. The sensors operate from 2.7 V to 18 V and provide digital outputs that can be connected directly to a microcontroller or other digital circuit.Note: This version is not compatible with the HPCB micro metal gearmotors; it is only compatible with LP, MP, and HP dual-shaft micro metal gearmotors.

Discontinuation notice: This encoder is not compatible with our HPCB micro metal gearmotors (the HPCB motor terminals are too large to fit the corresponding PCB holes), but it is compatible with the LP, MP, and HP versions of our micro metal gearmotors. We have released a new version of this board that enlarges the motor terminal holes so they are compatible with all our micro metal gearmotors. The new version is functionally identical to this older version and can serve as a drop-in replacement. We will be discontinuing this product when the remaining stock is gone.

These older encoders are now only available by large-volume special order. Please contact us for more information.

Magnetic Encoder Kit for Micro Metal Gearmotors (old version; not compatible with HPCB micro metal gearmotors).

Magnetic Encoder Kit for Micro Metal Gearmotors (HPCB compatible).

This kit includes two dual-channel Hall Effect sensor boards and two 6-pole magnetic discs that can be used to add quadrature encoding to two micro metal gearmotors with extended back shafts (motors are not included with this kit). The encoder board senses the rotation of the magnetic disc and provides a resolution of 12 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the gearbox output shaft, multiply the gear ratio by 12.

This compact encoder solution fits within the 12 mm × 10 mm cross section of the motors on three of the four sides, and it only extends 0.6 mm past the edge of the fourth side (note: if you need it to be flush with that last side, you can carefully grind the board down a little and solder to the remaining half-holes). The assembly does not extend past the end of the extended motor shaft, which protrudes 5 mm beyond the plastic end cap on the back of the motor.

Note: This sensor system is intended for users comfortable with the physical encoder installation. It only works with micro metal gearmotors that have extended back shafts.

The encoder board is designed to be soldered directly to the back of the motor, with the back shaft of the motor protruding through the hole in the middle of the circuit board. One way to achieve good alignment between the board and the motor is to tack down the board to one motor pin and to solder the other pin only when the board is flat and well aligned. Be careful to avoid prolonged heating of the motor pins, which could deform the plastic end cap of the motor or the motor brushes. Once the board is soldered down to the two terminals, the motor leads are connected to the M1 and M2 pads along the edge of the board; the remaining four pads are used to power the sensors and access the two quadrature outputs:

The sensors are powered through the VCC and GND pins. VCC can be 2.7 V to 18 V, and the quadrature outputs A and B are digital signals that are either driven low (0 V) by the sensors or pulled to VCC through 10 kΩ pull-up resistors, depending on the applied magnetic field. The sensors’ comparators have built-in hysteresis, which prevents spurious signals in cases where the motor stops near a transition point.

Encoder A and B outputs of a magnetic encoder on a high-power (HP) micro metal gearmotor running at 6 V.

The board’s six pads have a 2 mm pitch, so they do not work with common 0.1″ connectors. One option for connecting to the board is to solder in individual wires, such as in the example below:

Alternatively, you can solder a 2mm-pitch connector to the board. The examples below show a male header, which gives you the option of making a detachable cable terminated by a 6-pin 2mm-pitch female header. If the pins are angled over the motor, as shown in the picture below, they will just barely protrude through the holes in the board. Note that in this orientation, there is room to plug in a female header even when our extended micro metal gearmotor bracket is being used.

If the pins are pointed away from the motor, they will need to be angled so that they sufficiently clear the magnetic disc. With a decent soldering iron, it is possible to solder them in this orientation even after the encoder has been installed on the motor.

Once the board is soldered to the motor, the magnetic encoder disc can be pushed onto the motor shaft. One easy way to accomplish this is to press the motor onto the disc while it is sitting on a flat surface, pushing until the shaft makes contact with that surface. The size of the gap between the encoder disc and the sensor board does not have a big impact on performance as long as the motor shaft is at least all the way through the disc.

This schematic is also available as a downloadable pdf (125k pdf).

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The six-channel Micro Maestro raises the performance bar for serial servo controllers with features such as a native USB interface and internal scripting control. Whether you want high-performance servo control (0.25μs resolution with built-in speed and acceleration control) or a general I/O controller (e.g. to interface with a sensor or ESC via your USB port), this tiny, versatile device will deliver. The fully assembled version ships with header pins installed.

For a full list of products shown in this video, see the blog post.

The Micro Maestro is the smallest of Pololu’s second-generation USB servo controllers. The Maestros are available in four sizes and can be purchased fully assembled or as partial kits:

Maestro family of USB servo controllers: Mini 24, Mini 18, Mini 12, and Micro 6.

Micro Maestro — fully assembled

Micro Maestro — partial kit

Mini Maestro 12 — fully assembled

Mini Maestro 12 — partial kit

Mini Maestro 18 — fully assembled

Mini Maestro 18 — partial kit

Mini Maestro 24 — fully assembled

Mini Maestro 24 — partial kit

The Mini Maestros offer higher channel counts and some additional features (see the Maestro comparison table below for details).

Micro Maestro 6-channel USB servo controller bottom view with quarter for size reference.

The Micro Maestro is a highly versatile servo controller and general-purpose I/O board in a highly compact (0.85"×1.20") package. It supports three control methods: USB for direct connection to a computer, TTL serial for use with embedded systems, and internal scripting for self-contained, host controller-free applications. The channels can be configured as servo outputs for use with radio control (RC) servos or electronic speed controls (ESCs), as digital outputs, or as analog inputs. The extremely precise, high-resolution servo pulses have a jitter of less than 200 ns, making these servo controllers well suited for high-performance applications such as robotics and animatronics, and built-in speed and acceleration control for each channel make it easy to achieve smooth, seamless movements without requiring the control source to constantly compute and stream intermediate position updates to the Micro Maestro. Units can be daisy-chained with additional Pololu servo and motor controllers on a single serial line.

A free configuration and control program is available for Windows and Linux, making it simple to configure and test the device over USB, create sequences of servo movements for animatronics or walking robots, and write, step through, and run scripts stored in the servo controller. The Micro Maestro’s 1 KB of internal script memory allows storage of servo positions that can be automatically played back without any computer or external microcontroller connected.

Because the Micro Maestro’s channels can also be used as general-purpose digital outputs and analog inputs, they provide an easy way to read sensors and control peripherals directly from a PC over USB, and these channels can be used with the scripting system to enable creation of self-contained animatronic displays that respond to external stimuli and trigger additional events beyond just moving servos.

Bottom view with dimensions (in inches) of Pololu Micro and Mini Maestro servo controllers.

The Micro Maestro is available fully assembled with 0.1″ male header pins installed as shown in the product picture or as a partial kit, which ship with these header pins included but unsoldered, allowing the use of different gender connectors or wires to be soldered directly to the pads for lighter, more compact installations. The Mini Maestro 12, 18, and 24 are also available fully assembled or as partial kits. A USB A to mini-B cable (not included) is required to connect this device to a computer. The Micro and Mini Maestros have 0.086″ diameter mounting holes that work with #2 and M2 screws.

Micro Maestro 6-channel USB servo controller assembled.

Micro Maestro 6-channel USB servo controller partial kit.

Three control methods: USB, TTL (5V) serial, and internal scripting

0.25μs output pulse width resolution (corresponds to approximately 0.025° for a typical servo, which is beyond what the servo could resolve)

Pulse rate configurable from 33 to 100 Hz (2)

Wide pulse range of 64 to 3280 μs (2)

Individual speed and acceleration control for each channel

Channels can be optionally configured to go to a specified position or turn off on startup or error

Channels can also be used as general-purpose digital outputs or analog inputs

A simple scripting language lets you program the controller to perform complex actions even after its USB and serial connections are removed

Comprehensive user’s guide

Free configuration and control application for Windows makes it easy to:

Configure and test your controller

Create, run, and save sequences of servo movements for animatronics and walking robots

Write, step through, and run scripts stored in the servo controller

Configure and test your controller

Create, run, and save sequences of servo movements for animatronics and walking robots

Write, step through, and run scripts stored in the servo controller

Two ways to write software to control the Maestro from a PC:

Virtual COM port makes it easy to send serial commands from any development environment that supports serial communication

Pololu USB Software Development Kit allows use of more advanced native USB commands and includes example code in C#, Visual Basic .NET, and Visual C++

Virtual COM port makes it easy to send serial commands from any development environment that supports serial communication

Pololu USB Software Development Kit allows use of more advanced native USB commands and includes example code in C#, Visual Basic .NET, and Visual C++

TTL serial features:

Supports 300 – 200000 bps in fixed-baud mode, 300 – 115200 bps in autodetect-baud mode (2)

Simultaneously supports the Pololu protocol, which gives access to advanced functionality, and the simpler Scott Edwards MiniSSC II protocol (there is no need to configure the device for a particular protocol mode)

Can be daisy-chained with other Pololu servo and motor controllers using a single serial transmit line

Can function as a general-purpose USB-to-TTL serial adapter for projects controlled from a PC

Supports 300 – 200000 bps in fixed-baud mode, 300 – 115200 bps in autodetect-baud mode (2)

Simultaneously supports the Pololu protocol, which gives access to advanced functionality, and the simpler Scott Edwards MiniSSC II protocol (there is no need to configure the device for a particular protocol mode)

Can be daisy-chained with other Pololu servo and motor controllers using a single serial transmit line

Can function as a general-purpose USB-to-TTL serial adapter for projects controlled from a PC

Our Maestro Arduino library makes it easier to get started controlling a Maestro from an Arduino or compatible boards like our A-Stars

Board can be powered off of USB or a 5 – 16 V battery, and it makes the regulated 5V available to the user

Compact size of 0.85" × 1.20" (2.16 × 3.05 cm) and light weight of 0.17 oz (4.8 g) with headers

Upgradable firmware

1 This is the weight of the board without header pins or terminal blocks.

2 The available pulse rate and range depend on each other and factors such as baud rate and number of channels used. See the Maestro User’s Guide for details.

3 The user script system is more powerful on the Mini Maestro than on the Micro Maestro. See See the Maestro User’s Guide for details.

The Micro and Mini Maestros are available with through-hole connectors preinstalled or as partial kits, with the through-hole connectors included but not soldered in. The preassembled versions are appropriate for those who want to be able to use the product without having to solder anything or who are happy with the default connector configuration, while the partial kit versions enable the installation of custom connectors, such as right-angle headers that allow servos to be plugged in from the side rather than the top, or colored header pins that make it easier to tell which way to plug in the servo cables. The following picture shows an example of a partial-kit version of the 24-channel Mini Maestro assembled with colored male header pins:

24-channel Mini Maestro (partial kit version) assembled with colored male header pins.

Micro Maestro as the brains of a tiny hexapod robot.

Serial servo controller for multi-servo projects (e.g. robot arms, animatronics) based on BASIC Stamp or Arduino platforms.

PC-based servo control over USB port

PC-based control of motors by interfacing with an ESC over USB

PC interface for sensors and other electronics:

Read a gyro or accelerometer from a PC for novel user interfaces

Read a gyro or accelerometer from a PC for novel user interfaces

General I/O expansion for microcontroller projects

Programmable, self-contained Halloween or Christmas display controller that responds to sensors. The picture to the right and the video below show a self-contained hexapod robot that uses three micro servos and two digital distance sensors for autonomous walking.

Self-contained servo tester

An example setup using a Micro Maestro to control a ShiftBar and Satellite LED Module is shown in the picture below and one of the videos above. Maestro source code to control a ShiftBar or ShiftBrite is available in the Example scripts section of the Maestro User’s guide.

Connecting the Micro Maestro to a chain of ShiftBars. A single 12V supply powers all of the devices.

People often buy this product together with:

This small, inexpensive motor controller allows variable speed and direction control of two small, brushed DC motors using a simple serial interface, making it easy to add motors to your microcontroller- or computer-based project. The motor supply voltage range is 4.5 to 13.5 V; the continuous current per channel is up to 1 A (3 A peak). The logic supply can be as low as 2.7 V, allowing operation with modern microcontrollers running at 3.3 V.

The qik 2s9v1 is Pololu’s second-generation dual serial motor controller. The compact module allows any microcontroller or computer with a serial port (external RS-232 level converter required) or USB-to-serial adapter to easily drive two small, brushed DC motors with full direction and speed control. It provides ultrasonic, 8-bit PWM speed control via an advanced, two-way serial protocol that features automatic baud rate detection up to 38.4 kbps and optional CRC error checking. Two status LEDs give visual feedback about the serial connection and any encountered error conditions, making debugging easy, and a demo mode allows easy verification of proper operation.

The improvements over the previous generation and competing products include:

high-frequency (ultrasonic) PWM to eliminate switching-induced motor shaft hum or whine

a robust, high-speed communication protocol with user-configurable error condition response

visible LEDs and a demo mode to help troubleshoot problematic installations

reverse power protection on the motor supply (not on the logic supply)

For a more advanced, higher-power version of this controller, please consider the qik 2s12v10. For a simpler carrier of the qik’s motor driver, please consider the TB6612FNG dual motor driver carrier, and for a robot controller based on the qik’s driver, please consider the Baby Orangutan and Orangutan SV-328 robot controllers and 3pi robot, which connect the TB6612 to a user-programmable AVR microcontroller.

November 27, 2013 update: We have changed this product by replacing the large, silver electrolytic capacitor with a much smaller ceramic capacitor. This lowers the profile of the board but does not affect functionality at all. The main product picture shows this new version; the rest of the pictures on this product page still show the previous version with the tall electrolytic capacitor.

Simple bidirectional control of two DC brush motors.

4.5 V to 13.5 V motor supply range.

1 A maximum continuous current per motor (3 A peak).

2.7 V to 5.5 V logic supply range.

Logic-level, non-inverted, two-way serial control for easy connection to microcontrollers or robot controllers.

Optional automatic baud rate detection.

Two on-board indicator LEDs (status/heartbeat and serial error indicator) for debugging and feedback.

Serial error output to make it easier for the main controller to recover from a serial error condition.

Jumper-enabled demo mode allows initial testing without any programming.

Optional CRC error detection eliminates serial errors caused by noise or software faults.

Optional motor shutdown on serial error or timeout for additional safety.

Supports daisy-chaining the qik to other qiks and Pololu serial motor and servo controllers, allowing the control of up to hundreds of motors and servos with a single serial line.

Comprehensive user’s guide.

The qik ships with a 16×1 straight 0.100" male header strip, a 12×1 right angle 0.100" male header strip, and two red shorting blocks. This hardware offers several options when it comes to making connections to the qik.

For the most compact installation, wires can be directly soldered to the qik pins themselves. For less permanent connections, the 16×1 straight header strip can be broken into a 12×1 piece and two 2×1 pieces. The 2×1 pieces can optionally be soldered into the jumper pins, and the 12×1 header strip of your choice can be soldered into the qik control pins. This allows connections to the qik via custom-made cables that have female headers on them, or the qik can simply be plugged into a breadboard. Using the right angle header allows for a compact profile or for vertical mounting into a breadboard; using the straight header allows for breadboarding as shown in the picture above.

We have written a basic Arduino library for the qik dual serial motor controllers that makes it simple to interface these controllers with an Arduino. The library handles the details of serial communication with the qik, allowing two brushed DC motors to be controlled easily.

People often buy this product together with:

The QTR-1RC reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 0.5" x 0.3" module that can be mounted almost anywhere and is great for edge detection and line following. The output is designed to be measured by a digital I/O line. This sensor is sold in packs of two units.

Note: The QTR-1RC reflectance sensor requires a digital I/O line to take readings. The similar QTR-1A reflectance sensor is available with an analog output.

Functional description

The Pololu QTR-1RC reflectance sensor carries a single infrared (IR) LED and phototransistor pair. To use the sensor, you must first charge the output node by applying a voltage to the OUT pin. You can then read the reflectance by withdrawing the externally supplied voltage and timing how long it takes the output voltage to decay due to the integrated phototransistor. Shorter decay time is an indication of greater reflection. This measurement approach has several advantages, especially when multiple units are used:

No analog-to-digital converter (ADC) is required

Improved sensitivity over voltage-divider analog output

Parallel reading of multiple sensors is possible with most microcontrollers

The LED current-limiting resistor is set to deliver approximately 17 mA to the LED when VIN is 5 V. The current requirement can be met by some microcontroller I/O lines, allowing the sensor to be powered up and down through an I/O line to conserve power.

This sensor was designed to be used with the board parallel to the surface being sensed. Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection.

For a line sensor with eight of these units arranged in a row, please see the QTR-8RC reflectance sensor array; for a similar array of three slightly different sensor components, see the QTR-3RC. For a similar, smaller sensor with longer range, and intended for use with the board perpendicular to the surface, please see the QTR-L-1RC reflectance sensor.

QTR sensor size comparison. Clockwise from top left: QTR-3RC, QTR-1RC, QTR-L-1RC, QTR-8RC.

Specifications

Dimensions: 0.3" x 0.5" x 0.1" (without optional header pins installed)

Operating voltage: 5.0 V

Supply current: 17 mA

Output format: digital I/O-compatible signal that can be read as a timed high pulse

Optimal sensing distance: 0.125" (3 mm)

Maximum recommended sensing distance: 0.375" (9.5 mm)

Weight without header pins: 0.008 oz (0.2 g)

QTR-1RC output (yellow) when 1/8" above a black line and microcontroller timing of that output (blue).

Interfacing the QTR-1RC output to a digital I/O line

Like the Parallax QTI, this sensor requires a digital I/O line capable of driving the output line high and then measuring the time for the output voltage to decay. The typical sequence for reading a sensor is:

Set the I/O line to an output and drive it high.

Allow at least 10 μs for the sensor output to rise.

Make the I/O line an input (high impedance).

Measure the time for the voltage to decay by waiting for the I/O line to go low.

These steps can typically be executed in parallel on multiple I/O lines.

With a strong reflectance, the decay time can be as low as several dozen microseconds; with no reflectance, the decay time can be up to a few milliseconds. The exact time of the decay depends on your microcontroller’s I/O line characteristics. Meaningful results can be available within 1 ms in typical cases (i.e. when not trying to measure subtle differences in low-reflectance scenarios), allowing up to 1 kHz sampling.

Our Pololu AVR library provides functions that make it easy to use these sensors with our Orangutan robot controllers; please see the QTR Reflectance Sensors section of our library command reference for more information. We also have a Arduino library for these sensors.

Included components

This module has a single mounting hole intended for a #2 screw (not included); if this mounting hole is not needed, this portion of the PCB can be ground off to make the unit even smaller. Each pack of two reflectance sensors includes sets of straight male header strips and right-angle male header strips, which allow you to mount them in the orientation of your choice (note: the header pins might ship as 1×6 strips that you can break into two 1×3 pieces). You can also solder wires, such as ribbon cable, directly to the pads for the most compact installation.

How it works in detail

With only four components (or five, if you count the coupled IR LED and phototransistor separately), the operation of this sensor is relatively basic. The emitter side is just an IR LED with an appropriate current-limiting resistor. The light from the emitter leaves the sensor, reflects off a nearby surface, and returns to the detector.

The detector side is a resistor-capacitor (RC) circuit, where the resistance comes from the phototransistor and is a measure of the incident infrared light, and the decay time is proportional to the resistance. The first step of the sensor-reading process—driving the sensor output high—discharges the integrated 10 nF capacitor and puts both sides at the same voltage (VIN). Alternatively, you can think of this as “charging the output node”, and it is functionally equivalent to charging a capacitor with one side connected to ground. Once you are no longer supplying an external voltage to the output pin, the capacitor can slowly charge through the phototransistor, with the rate of charging being a function of the phototransistor’s resistance (which is in turn a function of the incident IR). As the capacitor charges, the voltage on the output side drops, eventually reaching zero when the capacitor is fully charged. Alternatively, you can think of this as “discharging the output node”, and it is functionally equivalent to discharging a capacitor with one side connected to ground.

The 220 Ω resistor on the OUT line serves to limit the current flow, making it possible for a microcontroller output to safely charge the output node prior to each reading. It has very little effect on the sensor output.

QTR-1RC and QTR-L-1RC reflectance sensor schematic diagram.

QTR-1RC output (yellow) when 1/8" above a white/black interface and microcontroller timing of that output (blue).

People often buy this product together with: