Java程序辅导
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
Biomedical Engineering Summer School EL#1 - 1 © Electronics and Computer Science, University of Southampton Page 1 of 10 Biomedical Electronics Summer School BIO-EL Lab #1: Optical Heartrate Sensor In this lab you will construct the electronic circuit to measure heartrate optically. The board has a red, light emitting diode (LED) that will flash to indicate your heartrate. This exercise introduces techniques for constructing an electronic circuit, and techniques for testing the hardware with laboratory test equipment. Biomedical Engineering Summer School EL#1 - 2 © Electronics and Computer Science, University of Southampton Page 2 of 10 Schedule Lab time : 1.5 hours Items provided Tools : Soldering Iron and Iron stand + safety glasses Solder Desoldering tool Side cutters Wire strippper Needle noise pliers Components : 1x Heartrate printed circuit board Integrated circuit (IC): 1x MCP602 Resistors: 3x 680kΩ, 1x 68K, 1x 47kΩ, 2x 6.8kΩ, 2x 1kΩ Capacitors: 1x 1µF (blue), 3x 100nF (yellow) Switch 1x micro DPDT 1x 5mm Red LED 1x IR sensor (Black case) Equipment : Multimeter and cables Power Supply Oscilloscope + probe • You will work in pairs for this laboratory exercise, but you will each solder your own PCB. • Before starting, we recommend that you have a quick read through all sections of these notes so that you have an idea of what you are going to be doing in the lab. • Be careful – the tip of the soldering iron is very hot! Revision History July 30, 2023 July 23, 2023 July 11, 2022 July 18, 2019 July 16, 2018 Dr Russel Torah – updated R9 to be 1k Dr Russel Torah – update tools and other fixes Dr Daniel Spencer – minor amendments Dr Daniel Spencer (dcs) – new PCB design Dr Daniel Spencer (dcs) Version 2.3 Version 2.2 Version 2.1 Version 2.0 Version 1.0 Biomedical Engineering Summer School EL#1 - 3 © Electronics and Computer Science, University of Southampton Page 3 of 10 1 Your Lab Exercise: Heartrate sensor You start with a bare printed circuit board, insert the components and then solder the components in place. You will learn and apply the techniques of soldering to assemble the components onto a double-sided printed circuit board (PCB). After the circuit is built, it is essential to test it to see that it operates correctly. A circuit can fail for a number of reasons, including poor soldering (dry joints or solder bridges), components in the wrong place, components the wrong way round, faulty components or a poorly fabricated PCB. To test the circuit you will use a bench PSU, a digital multimeter and an oscilloscope and a logic analyser. This will give you the opportunity to learn how to use these instruments. 1.1 How to solder Start by watching this short video on how to solder and some tips: https://www.youtube.com/watch?v=Qps9woUGkvI Next, ask a mentor to show you and help set up the solder station. You will be provided with a small piece of strip board and some resistors to get the hang of soldering before you solder on the PCB. Have a few goes until you’re happy you have the hang of it. 2 Circuit Components 2.1 Printed circuit board Electronic circuits can be constructed using a number of technologies: breadboard, tri-pad, stripboard, wire-wrap, PCB, or dead-bug. For simple prototyping of new designs a breadboard can be a convenient method, but it is limited to low-speed circuits. Some modern components are only available in fine pitched surface mount devices which don’t fit on a breadboard. A PCB is a multi-layer board, with each layer containing a number of copper tracks connecting the components as defined in the schematic. Simple boards are often two-layer with tracks on the top and bottom. Have a look at the heartrate PCB – can you see the track which connects the battery to the switch? Boards designed for more demanding applications (such as in a mobile phone) are very similar, but with many more layers (4, 6 or 8 being common) sandwiched inside the board and connections made with vias. The board has been designed to use the plated through holes (PTH) for the components to join the two layers together at appropriate points on the board. 2.2 Components Components are generally divided into two categories: those that have wires or legs that are pushed through the board and soldered underneath (called through-hole) and those that lie on the surface of the board and are soldered on the same side (called surface mount). The board you are going to solder is through hole which is the easiest to solder as the components are usually larger. Which type of package to use in a design depends upon a number of factors including component availability (modern devices are often only available as SMDs), assembly method (automatic Biomedical Engineering Summer School EL#1 - 4 © Electronics and Computer Science, University of Southampton Page 4 of 10 pick-and-place machines may prefer SMDs) and circuit size (SMDs can achieve a much higher density by their small size and assembly on both sides of the board). The design contains a number of commonly used electronic components: • Resistor: A device for limiting the flow of current. For through-hole resistors the value is usually indicated by a set of colour codes. The device is not polarised which means that it may be installed either way round. • Capacitor: A device for storing charge; often used for filtering and improving the local quality of power sources. The value and maximum voltage rating is normally written on the component. They can be polarised (typically values ≥ 1µF) or un-polarised. • Switch: A device for selecting between a number of possible circuit configurations. A common terminology is mPnT, where m describes the number of linked switches in the package and n describes the number of positions each switch can take, e.g. SPDT denotes a Single Pole Double Throw switch. • LED (Light Emitting Diode): A polarised device which illuminates when current flows through it in the correct direction. • IC (Integrated Circuit): A multi-leaded package containing internal circuitry – often containing thousands or millions of components. Devices range from relatively simple voltage regulators with three pins to high performance microprocessors with many hundreds of pins. 3 Soldering the components 1. Place the iron in good contact with both the pad and component lead. 2. Wait a couple of seconds for both pad and component to reach temperature. 3. Add a little solder to the joint, taking care not to add the solder to the iron tip, but aim it to meet the junction of the pad and the lead. 4. Add enough solder that the joint forms a volcano shape (figure 2A). 5. Remove the solder. 6. Remove the iron. 7. Ensure that the component lead is not moved while the solder cools (five seconds is enough) or the joint will fracture creating a dry joint. 8. Inspect the joint and ensure that it is shiny. If not reheat and add a little more solder to introduce some new flux. 9. Use the side-cutters to remove the excess lead, cupping your hand over the board as you do so to avoid the lead becoming a projectile. 3.1 Removing a solder bridge Modern PCBs contain a solder mask which helps to minimise the chances of an accidental bridge between two adjacent pads. However, when soldering fine pitch devices it may occur. Use a length of solder wick to absorb the excess solder, by touching the wick and iron over the offending area. Biomedical Engineering Summer School EL#1 - 5 © Electronics and Computer Science, University of Southampton Page 5 of 10 4 Assembly 4.1 Preparation Start by laying out the components from the kit on a piece of paper and identify their values. Write down the component identifiers next to each component and ensure that none are missing. You can use your multimeter set to its resistance range to confirm the resistor values: Plug the two cables from the draw underneath the bench into the multimeter as per the figure below. Press the “Ω” button to measure resistance. 4.2 IC Socket Insert the 8-pin socket (NOT the IC) ensuring that the pin 1 indicator corresponds to the PCB indication. Turn over the PCB so that it rests on the socket. Solder two diagonally opposite pins. Now turn the board over and confirm that the socket is flush with the board. If not, turn over and gently reheat the offending pin whilst applying a little downward pressure to the PCB. You can now solder the remaining 4 pins knowing that the socket is correctly inserted. If you have never soldered before, ask one of the demonstrators to take a look at your first few solder joints for feedback on your technique, before you proceed too far. Biomedical Engineering Summer School EL#1 - 6 © Electronics and Computer Science, University of Southampton Page 6 of 10 4.3 Resistors Resistors are two-leaded components have no polarity and can be inserted either way round. If you wish to be precise you can insert the resistors so that their colour codes read from left to right (or top to bottom). Ask a demonstrator to help you setup the multimeter so that you can check the value of each resistor. Insert one of the 680kΩ resistors into R1. Turn over the board, and secure the component in place before soldering when required by bending the legs slightly. Alternatively you can hold these down with bluetac. Next, solder the connections to hold the component in place. Now, turn over the board and check the resistor is sitting flat on the board. If not, you can heat one side with the soldering iron and press through the component. You can ask demonstrator to help you with this. Remove the two pieces of surplus wire from the soldered components using the cutters. Hold, or place your hand over, the lead you are cutting to avoid it flying off as a projectile. Next, repeat for the remaining two 680kΩ resistors which go into R2 and R4 Biomedical Engineering Summer School EL#1 - 7 © Electronics and Computer Science, University of Southampton Page 7 of 10 Solder the 68kΩ resistor into the slot for R3 Solder the remaining resistors: R5 =47kΩ R6 =6.8kΩ R7 = 6.8kΩ R8 = 1kΩ R9 = 1kΩ 4.4 Capacitors Some types of capacitors are polarised, which means they must be inserted in the correct orientation (they have one positive, and one negative terminal). The capacitors in this design are non-polarised which means it does not matter which way round they are inserted. C1, C2 and C3 are 100nF capacitors. These are all yellow. If you have very good eyesight, you may be able to read the marking as “104” which means 10 followed by 4 zeros, i.e. 100,000 pF which is 100nF (1nF=1000pF). C4 is a 1µF capacitor. This is blue. If you have very good eyesight, you may be able to read the marking as “105” which means 10 followed by 5 zeros, i.e. 1,000,000 pF which is 1µF. 4.5 LED and Photosensor The red LED has two pins and must be inserted in the correct orientation in the holes marked LED1. The photosensor (black rectangular package with four pins) contains an infrared LED and Phototransistor and must be inserted the correct orientation in Q1. If you are unsure, check with a demonstrator. The red LED should be inserted with the flat edge matching the flat of the white silkscreen on the board. Biomedical Engineering Summer School EL#1 - 8 © Electronics and Computer Science, University of Southampton Page 8 of 10 The LED/phototransitor package should be inserted such that the two circles face upwards. You might need to use the needle nose pliers to help gently bend the legs to fit in the PCB holes, be careful not to break them. 4.6 Switch Insert the switch into the socket marked power and solder. The switch can go in either orientation. Insert the switch into the board and solder 5 Testing Before plugging in a power supply, we need to check the circuit. Take the Check the resistance between point A and point B. It should be approximately 0.7MΩ Now check the resistance between points A and C. It should be approximately 6.8KΩ Biomedical Engineering Summer School EL#1 - 9 © Electronics and Computer Science, University of Southampton Page 9 of 10 Continue checking the resistance between point A and the IC socket (labelled anti-clockwise from B to H. A→D ≈68KΩ A→E should be less than 1Ω A→F ≈1.4MΩ A→G ≈18KΩ A→H ≈0.7MΩ A→I should be greater than 2MΩ Insert the black integrated circuit (IC) into the socket, checking with a demonstrator that the orientation is correct. The semi-circle or dot at the top of the IC should be orientated with the semi-circle on the socket. 5.1 Power Next, you are going to power on the board using a benchtop power supply. Cut, strip and solder a length of red wire (~50cm) to the back of the board, labelled “VCC” and a black wire to ground (GND) as shown in the figure below. You should strip about 1cm of the plastic wire insulation from both ends, ask for help from the demonstrators if you’re unsure how to strip the wire. Do not plug in the board to the power supply until step 4 below. 1. Turn on the power supply using the switch in the bottom left corner. 2. Ensure the button in the bottom right corner is depressed 3. Rotate the dials until they read 3.00 (Volts) and 0.020 (Amps) 4. Plug in the red and black wires to + and – respectively (figure below) 5. Check that the dials still read 3.00V and 0.020 (Amps) 6. Finally, press the button circled in yellow on the power supply. Biomedical Engineering Summer School EL#1 - 10 © Electronics and Computer Science, University of Southampton Page 10 of 10 5.2 Heartrate measurements • Hold your finger over the photo sensor. You need to hold very still and wait for 10 seconds for the reading to stabilise. The red LED should flash in time with your heartrate. • Now try using different fingers. 6 Further work If you have time, ask a demonstrator how to connect the circuit up to an oscilloscope to see the signal. Note: Measuring heartrate optically is very challenging. The circuit is fairly simple, and demonstrates some of the challenges in measuring and processing bio-signals. The circuit has a very high gain to measure the faint signals and the circuit is prone to oscillation. You will need to keep very still, as movement changes the amount of light absorbed. For best results, put the board flat on the bench and press lightly on the sensor. 6.1 Battery power If you have time towards the end of the lab, you can remove the power wires and solder the coin- battery holder. Ask a demonstrator to help you with this.