Transcript Electronics
Underpinning Knowledge Questions What are the specific safety practices and procedures that you need to observe when assembling and testing electronic circuits? (To include: any specific legislation, regulations or codes of practice for the activities, equipment or materials.) Is the test equipment in good condition? Are the test leads for the equipment in a safe condition, no nicks or breaks in the insulation? Have you tested the test equipment on a known working electrical supply before connecting it to your circuit? Has the test equipment been recently calibrated? Have you been trained to carry out this task? Do you have the skills? Are you wearing the correct PPE to complete this task? Are you practising safe soldering techniques, perhaps you could describe a safe and effective soldering procedure? Are the tools you are using to form and trim the component leads maintained in a safe condition? If you are making a PCB, are you following the correct procedures? What are the hazards associated with assembling and testing electronic circuits and how can they be minimised? (Such as: heat, toxic fumes, spilled / splashed chemicals / solder, static electricity, using sharp instruments for stripping cable insula What are the hazards associated with assembling and testing electronic circuits and how can they be minimised? (Such as: heat, toxic fumes, spilled / splashed chemicals / solder, static electricity, using sharp instruments for stripping cable insulation, connecting clips / probes into circuits.) Are you using ventilation next to your circuit? Are you wearing eye protection when making PCB boards and trimming component leads? Have you selected the correct components and checked them against a data sheet? How can you minimize the risk of static damage to a circuit containing integrated components? Is the PPE you are wearing suitable for the job? Have the tools you are using been maintained in a safe condition? Are you using a heat shunt when soldering delicate components such as transistors? Have you tested a circuit with the correct test equipment to ensure it electrically dead prior to handling it? Perhaps you could describe the correct procedure for setting up a multimeter to test for current, voltage and resistance (each one is different) Are testing the circuit with the correct voltage and power supply? Have you tested for short circuits and open circuits (perhaps you could describe the difference between them) Why is it important to wear appropriate protective clothing and equipment? Why is it important to keep the work area safe and tidy? To protect your clothes? To protect your skin and eyes, for example repeated exposure to some chemicals can cause dermatitis and cancer To protect your lungs and respiratory system from dangerous fumes and gases Are you using a barrier cream to minimize skin contact with the chemicals used to make the PCB’s If you have an accident whilst making PCB’s and were not using the correct PPE, do you think you will have grounds for compensation? If someone else has an accident because of your negligence, do you think they will have grounds to seek compensation from you? Does a messy and untidy workplace assist you in making circuits? Is a messy and untidy workplace likely to contribute to accidents? Whose responsibility is it to ensure the workplace is in a safe and tidy condition? If you spot an unsafe practice, what would you do? Is it your responsibility to report hazards to an appropriate person? What precautions do you need to take to prevent electrostatic discharge (ESD) damage to circuits and sensitive components? (Such as: use of earthed wrist straps, anti-static mats, special packaging and handling areas.) Use wrist straps that can be earthed Wear anti static boots and clothing that is less likely to cause a build up of static charge Stand on anti static mats when assembling circuits How do you use and extract information in relation to work undertaken? (To include: circuit diagrams, block and schematic diagrams, equipment manuals, data sheets, test procedures and instructions [to include: symbols and conventions to appropriate BS or ISO standards].) Read circuits diagrams and list all of the components required Check component values using charts, British standards and data sheets Check component tolerances once again using charts and data sheets Check component symbols against BS EN60617 Recognize that not every drawing you encounter will use BS circuit symbols, for example some circuits use ANSI symbols (American National Standards Insitute) Use the circuit diagram to plan a layout for your circuit taking into account the size and proximity of various components Check your circuit design against the layout for every stage of the design process How do you recognise, read the values and identify polarity and any other orientation requirements for all electronic components being used in the assemblies? (Such as: capacitors, resistors, inductors, diodes, transistors, integrated circuit chips, and other discrete through-hole or surface-mounted components.) Check resistor values using the resistor colour code Check resistor tolerance values using the colour code and double check with a multimeter Use pin out diagrams to identify the function of pins on integrated circuits e.g. Power , ground, input and output Use data sheets to identify the polarity of the terminals on diodes Describe the difference between through hole and surfact mount components (such as size, reading component values and the absence of component leads on surface mount components) Check capacitor values using a chart, internet resources or data sheets Check polarity dependant components are connected the right way around (longer leg is connected to positive) Describe how the polarity of electrolytic capacitors and LED’s can be established How do you check that components meet the required specification / operating conditions? (Such as: values tolerance, current carrying capacity, voltage rating, power rating, working temperature range.) Check information from the circuit diagram which should contain the required information Check data sheets to find the current carrying capacity of components Check data sheets for working temperature range Often working voltages are stamped on components such as capacitors Power rating: How do you check the power rating of a resistor? What is the power rating the general purpose resistors used in the laboratory (.25 Watt) What are the basic principles of operation of the electronic circuits being assembled? The amplifier takes a small input signal from a source such as an ipod or mp3 player and reproduces the signal at its output. The signal at the output is much larger than the input (thats what amplify means) which allows it to drive a loudspeaker. The fuse tester can also be used to test the continuity of a circuit. It uses a NOR gate to detect whether the fuse is good. If the fuse is good the NOR gate gives an output voltage of 5 volts. This voltage is used to switch on a transistor which drives a 555 timer and an LED. The 555 timer gives out a high pitched tone if the fuse is working and the LED lights up. The H bridge stepper motor control circuit uses 8 transistors to control the current through both phases of the stepper motor. The current must be fed to the stepper motor in the correct sequence in order for it to run forwards and backwards. A microcontroller is programmed to switch the transistors on and off. The entire circuit is powered through a bridge rectifier and voltage regulator which gives power to the microcontroller. The stepper motor power is taken from a point directly before the regulator as +12 volts smoothed DC. The amplifier takes a small input signal from a source such as an ipod or mp3 player and reproduces the signal at its output. The signal at the output is much larger than the input (thats what amplify means) which allows it to drive a loudspeaker. The fuse tester can also be used to test the continuity of a circuit. It uses a NOR gate to detect whether the fuse is good. If the fuse is good the NOR gate gives an output voltage of 5 volts. This voltage is used to switch on a transistor which drives a 555 timer and an LED. The 555 timer gives out a high pitched tone if the fuse is working and the LED lights up. The H bridge stepper motor control circuit uses 8 transistors to control the current through both phases of the stepper motor. The current must be fed to the stepper motor in the correct sequence in order for it to run forwards and backwards. A microcontroller is programmed to switch the transistors on and off. The entire circuit is powered through a bridge rectifier and voltage regulator which gives power to the microcontroller. The stepper motor power is taken from a point directly before the regulator as +12 volts smoothed DC.