REFLECTIVE PHOTOSENSOR CIRCUIT MODULE KIT ASSEMBLY GUIDE

Transcription

1 Pages from Reflective Photosensor Circuit Module Kit Assembly Guide: REFLECTIVE PHOTOSENSOR CIRCUIT MODULE KIT Introduction: ASSEMBLY GUIDE The Reflective Photosensor Circuit Module is a compact 1.6" by 1.2" two-layer circuit board that features the TCRT5000 Reflective Optical Sensor, manufactured by Vishay Semiconductors. While the board has very practical industrial applications as a non-contacting limit switch or proximity sensor, it is designed primarily for student experimentation. The board contains the familiar LM311P high-speed voltage comparator and a potentiometer that allows for sensitivity adjustment. The board provides a TTL compatible discrete (digital) output signal that pulses to a logic high when a reflective object approaches the sensor. A small (3mm) red LED indicator illuminates with this condition, serving as a visual aid in sensitivity adjustment. The board also contains easily accessible test points, allowing the student to monitor and compare the outputs of the TCRT5000 sensor and the sensitivity adjustment potentiometer. The board features two mounting holes for direct connection to equipment and also contains a right-angle pin header for easy attachment to a prototyping board. Figure 1 shows both the front and back sides of the fully assembled Reflective Photosensor Module. Figure 1 1

2 Objectives: By performing the assembly and testing procedures for the Reflective Photosensor Circuit Module Kit, the students should: Increase their skills in handling and soldering common through-hole electronic components. Gain familiarity with the design and fabrication of a two layer printed circuit board (PCB). Become familiar with a few techniques for testing the operation of electronic components. Become familiar with the structure and operation of the TCRT5000 Reflective Optical Sensor. Gain a fundamental knowledge of the operation of the LM311 high-speed voltage comparator Gain a fundamental knowledge of the design and operation of a transistor switch. Gain a fundamental knowledge of the design and operation of LED current control circuitry. Recommended Tools and Materials for Assembly of the Reflective Photosensor Circuit Module: 2 Figure 2 While not an absolute requirement, the Helping Hands tool shown above in Figure 2 is very handy for holding a PCB in the optimal position and freeing both hands during soldering. The Helping Hands is available through Marlin P. Jones & Assoc. Inc. (PN: 16037TL). A temperature controlled solder station is also recommended. (A 0.03" conical soldering tip also preferable for soldering through-hole components to the PCB.) Because the PCB is designed for assembly using leaded solder, a small container of MG Chemicals Pocket Pak solder (Sn63/Pb37 alloy) is included with this sampler kit (Mouser Electronics PN G). Because the application of a small amount of flux is recommended to expedite the soldering process, a Kester formula #2331-ZX neutral ph water soluble flux pen is included with this sampler kit (Mouser PN: ). To protect semiconductor components from excess heat during soldering, use of a clip on heat sink is advised. A Circuit Specialists clip on heat sink (PN: HT-156) is included with this sampler kit. For final cleaning of the PCB, an aerosol flux remover, such as E-LINE Flux Remover (10 oz aerosol ) is recommended (Mouser PN SB). Other recommended

3 items include a good pair shear cutters, and a role of painters tape (for holding components in place during soldering). Assembly Procedure for the Reflective Photosensor Circuit Module Kit: 1) Take a moment to view the three Tables and Figures sheets provided with this assembly procedure. Figure 1 shows the silk screening on the top side of the PCB, clearly indicating the location of each component. Table 1 identifies and defines several of the reference designators used for components contained on PRESSON Circuit Modules. Figure 2 of the Tables and Figures provides a more detailed view of the PCB, showing the location of solder pads and traces on the top and bottom layers. Tables 2 and 3 will be used extensively for component identification during this assembly procedure. 2) While referring to Tables 2 and 3 in the Tables and Figures sheets, open the kit package and carefully perform an inventory of its contents. If a Helping Hands is available, use the magnifying lens as necessary to identify the 1/8 resistors by their color bands and sort these components by their designators. (For additional practice, you could also use a multimeter to measure actual resistances.) For future reference, a link to a reliable 5-band resistor color code chart and calculator is provided below: Five-Band Band Resistor Color Codes 3) Insert transistor Q1 into its position on the PCB. Ensure that the part is oriented as shown in Figures 3 below. (Note that the kinked leads of Q1 limit the depth of insertion for this component.) Figure 3 4) Connect the clip-on heat sink across all three leads of transistor Q1, on the top side of the board, just below the black body of the part. Place a small strip of ScotchBlue tape across the top of the part to ensure it will remain in its fully inserted position. 3

4 Objectives: By performing the assembly and testing procedures for the Reflective Photosensor Circuit Module Kit, the students should: Gain familiarity with the design and fabrication of a two layer printed circuit board (PCB). Become familiar with a few techniques for testing the operation of electronic components. Become familiar with the structure and operation of the TCRT5000 Reflective Optical Sensor. Gain a fundamental knowledge of the operation of the LM311 high-speed voltage comparator Gain a fundamental knowledge of the design and operation of a transistor switch. Gain a fundamental knowledge of the design and operation of LED current control circuitry. Learn how to safely connect the Reflective Photosensor Circuit Module to a section of solderless breadboard. Learn how to test and adjust the sensitivity (detection range) of the Reflective Photosensor Circuit Module. Recommended Tools and Materials for Testing the Operation of the Reflective Photosensor Circuit Module: 4 Figure 2

5 Pages from Reflective Photosensor Circuit Module Kit Test Procedure: Testing Procedure for the Reflective Photosensor Circuit Module Kit: NOTE: Figure 3 shows two Reflective Photosensor Circuit Modules inserted into a breadboard section. Note that the pins of right angle header J1 are inserted directly into the breadboard. The +5.0VDC supply voltage is routed to pin 1 of J1 from the breadboard power bus. The power supply ground bus is routed to pin 3 of J1, connecting system ground to the ground plane of the module. With the PCB vertically positioned as seen here, the user has easy access to potentiometer R3 and the test point TP1 during system testing. Note that LED1 of the left-hand module is illuminating, indicating that the circuitry has detected the presence of the reflective paper in front of U1 on the opposite side of the board. With a +5.0VDC power source, the Proximity_Sense signal (pin 2 of J1) toggles to a logic high of nearly +4.5VDC during this condition. Figure 3 1) Cut short sections of the solid 18AWG red, green, and blue hookup wire (provided with the sampler kit). Strip the ends of these wire sections as necessary to fabricate the small breadboarding jumpers shown in Figure 4 on the following page. Connect these jumpers as shown there. NOTE: The black squares in Figure 4 indicate the positions of the three pins of right-angled header J1. These pin locations correspond to the J1 outputs specified in Figure 3 above. 5

6 Figure 4 2) Attach the Reflective Photosensor Circuit Module to the breadboard by inserting the three pins of connector J1 into the positions indicated by the black squares in Figure 4 (breadboard coordinates 4g, 5g, and 6g). Position the module with the top side facing toward the center of the breadboard (as seen with the left-hand module in Figure 3). 3) If a benchtop power supply is available, adjust its output to +5.0VDC prior to connecting it to the breadboard. Next, switch off the power supply and connect it to the +5VDC bus and the ground bus as indicated in Figure 4. Then proceed to step 5. 4) If the benchtop power supply is not available, consider using the simple solution for the +4.5VDC power source shown in Figure 5. Place the three alkaline AA batteries into the holder (provided with the sampler kit). Then connect its black (-) lead to the breadboard Power Supply Ground bus and the red (+) lead to the breadboard Power Supply +5VDC bus. Figure 5 6

7 Pages from Reflective Photosensor Circuit Module User s Manual: Reflective Photosensor Circuit Module Theory of Operation: The following is a detailed, component level introduction to the operation of the Reflective Photosensor Circuit Module. The lesson begins with an explanation of the structure and operation of the Vishay TCRT5000 Reflective Optical Sensor. We will refer to the technical datasheet for that device throughout this part of the discussion. The lesson continues with an overview of the operation of the module's comparator and LED indicator circuitry. Figure 4 below contains a diagram showing the operation of the TCRT5000 Reflective Optical Sensor. We will now search for additional technical data on this device to learn more details about its operation. We can find the manufacturer's datasheet for this product by returning to Mouser Electronics website ( Entering the manufacturer's part number (TCRT5000) in the Part # / Keyword box could produce two possible search results: Mouser parts 782-TCRT5000 and 782-TCRT5000L. It is important to note that these numbers represent the same product, the only difference being in the packaging method. (One is shipped in bulk, while the other is enclosed in a protective tube.) Click on the Datasheet link (for either part number) to access the manufacturer's PDF datasheet. (You should strongly consider downloading this documentation and saving it on your computer, possibly creating a file of manufacturer's datasheets for all devices you plan to use in future projects.) 7 Figure 4

8 The term infrared literally means "below" red, referring to that portion of the electromagnetic spectrum below the range of visible light. Infrared light is much preferred for optical signaling circuitry because it is fairly immune to changes in ambient visible light. In the bulleted FEATURES on page 1 of the datasheet we see the specification: Emitter wavelength: 950 nm (where nm represents nanometers). It is important to note that, in optoelectronics, the term "emitter" refers to the component within a device that actually emits the light. For the TCRT5000, the emitter is an infrared (IR) LED that produces a light beam with a wavelength of 950 nm. The FEATURES also identify the detector component within the TCRT5000 as a phototransistor. The phototransistor (left hand component in the symbolic diagram of the photosensor in Figure 4) has collector and emitter terminals. However, there is no base terminal. As the reflected 950 nm infrared light strikes the base material of the phototransistor, it stimulates the flow of collector current, from the C terminal of the TCRT5000. In addition to the small light-blocking barrier shown in Figure 4, the FEATURES also specify the daylight blocking filter action of the device, which is provided within the dome lens structure on the detector side of the device. Figure 5 below contains a schematic diagram of the circuitry contained on the PRESSON Reflective Photosensor Circuit Module. Figure 5 8