Product description: Trim with QTR-8RC reflective sensors - digital - Pololu 961
The system consists of eight reflective sensors (a pair: IR LED and phototransistor), it was designed to detect black line on a white background. The reading is done by measuring the discharge time of the capacitor, with which connected are phototransistors. With this solution, the user should not use the A/D converter.
IR LEDs were paired to reduce the current consumption. They are controlled through a MOSFET transistor - enabled with the high status, disabled with low status. Such solution allows you to turn off the LEDs when they are not in use and thus, reduce energy consumption.
The current of the single LED is in the range of 20-25 mA. The whole module consumes approx. 100mA.
Specification of the strap with reflective sensors
- Dimensions: 75 x 127 x 4 mm
- Supply voltage: 5 V or 3.3 V
- Supply current: 100 mA
- Signal on output: digital (compatible with the I/O pins)
- Maximum measurement distance: 9.5 mm
- Weight: 3,09 g
Diagram of the module
Diagram of the QTR-8RC strap
The value read from the sensor QTR-8RC
The reading is done by measuring the discharge time of the capacitor. With this solution, the user don't have to use the analog to digital converter.
A typical sequence of the reading of sensor values:
1. Enabling of the of IR LEDs (if previously disabled)
2. Setting the I/O pins of the microcontroller as output and the creation of a high status.
3. Wait at least 10us. (charging the capacitor of 10nF)
4. Setting the I/O pins as input (high impedance status)
5. Measuring the discharge time of the capacitor through waiting until the I/O lines switch to a low status.
6. Disabling the IR LEDs (optional).
The Pololu company created an AVR C/C++ library that simplifies the use of the products. The functions to support the QTR strap were also included.
Available is also the library for the Arduino project.
What's in the kit?
The kit includes the module with sensors, goldpin strap and the resistor of 100 Ohms.
There is the possibility of separating the strap into two parts. Both boards will work as separate units.
For the proper functioning of the smaller board, necessary is 100 Ohm resistor (included in the set). The item must be soldered as shown in the picture below: