Trigger Flash Coil Battery Charging Switch Lecture 9

Trigger Flash Coil Battery Charging Switch Lecture 9: Disposable Camera Learning Engineering Using Inexpensive Products That May Be Found Around The House Or Apartment or Dorm Room 3/9/2021 Introduction to Engineering Electronics K. A. Connor 1

Electrical Safety • Note on the diagram of the camera that voltages as high as 320 V exist in this circuit • It is current, not voltage, that heats a wire and that causes damage to humans. • The salty fluids of the human body are electrical conductors. • The interior resistance of an arm, from hand to shoulder is about 100 Ohms. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 2

Electrical Safety • Any voltage across the internal resistance will cause currents to flow and heat to be generated sufficient to cause damage to tissue. • Much more significantly, the nervous system and its means of control over muscles (including the heart) are electrochemical. Thus, damage can occur at currents much less than those necessary to cause burns. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 3

Electrical Safety: Current Physiological Reaction (60 Hz) 3/9/2021 < 1 m. A 1 -3 m. A 3 -10 m. A None Perception Threshold Mild Sensation Painful Sensation 10 m. A Paralysis Threshold of Arms 30 m. A 75 m. A 250 m. A 4 A >5 A Respiratory Paralysis Fibrillation Threshold (0. 5%) Fibrillation Threshold (99. 5%) Heart Paralysis Threshold Burning Introduction to Engineering Electronics K. A. Connor 4

Electrical Safety • One of the key characteristics that distinguishes an EE, CSE or EPE from other technical professionals is an understanding of electrical safety. • It is particularly important to be able to estimate currents from known voltages, since voltages are easier to measure and generally more controllable. • Thus, if you learn nothing else from IEE, you should learn that: § Ohm’s Law can save your life and the lives of others. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 5

Electrical Safety: How To Avoid Shock • Estimate voltages and currents and act cautiously. • Resistance of dry skin offers protection below 50 V. Typically, skin inserts 10 k to 100 k Ohms of resistance between an outside conductor and internal fluids. • Skin provides safe current limiting below 50 V if it is dry. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 6

Electrical Safety: How To Avoid Shock • When working with voltages above 100 V, exercise great care. • If you must work with these voltages, a famous rule is to keep one hand in your pocket because arm-to-arm current through your heart is much worse neurologically than local currents through one limb. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 7

Electrical Safety: References Remember the one hand rule • • MIT Lab Safety NASA Lab Safety Tecra Tools Electrical Safety University of Tennessee Power Electronics Lab Safety 3/9/2021 Introduction to Engineering Electronics K. A. Connor 8

Electrical Safety • It is possible to come in contact with high voltages with little permanent harm as long as currents are small. • Stun guns work at voltages typically between 20 k. V and 150 k. V and usually do not cause permanent damage since currents are small (a few microamps) and voltages are pulsed (1 microsecond). • We will return to the topic of stun guns at the end of this lecture. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 9

2 Minute Quiz Name_______ Sec___ • True or false – proper electrical safety procedures require that we always know at least approximately what currents we will encounter in a circuit. • In the disposable camera circuit, how long is the wire for the primary winding? How long is the wire for the secondary winding? 3/9/2021 Introduction to Engineering Electronics K. A. Connor 10

Disposable Camera Electronics • This is the circuit you will be building in the lab using a disposable camera. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 11

Disposable Camera Electronics Trigger Flash Coil Battery Charging Switch • This is the circuit mentioned in lecture 6 which can be used to launch a piece of a paper clip up to 50 feet. • The coil is soldered in series with the flash tube. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 12

Disposable Camera Electronics • There are many different types of disposable cameras. All open differently. • Once you remove the film for processing (this can be done by the developer), you can use the remaining circuit and battery. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 13

Disposable Camera Electronics Capacitor • Note that the capacitor can still be charged, even if the camera has not been used for a while. Many cameras automatically charge between shots. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 14

Disposable Camera Electronics Flash Tube Capacitor Transformer • The circuit board, once removed, is quite simple. • Shown above are both the top and bottom views of the circuit board. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 15

Disposable Camera Electronics • The cover can be pried off. • Once you remove the cover, observe how the mechanical apparatus works (gears, shutter, lens, springs, etc). • You may find these useful in applications. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 16

Disposable Camera Electronics • The Exploratorium recommends that you use rubber gloves to avoid shock. • Pry off the case using a screwdriver • You should be able to set the shutter mechanism using intact gears, etc. • You can recharge the capacitor using the charge button (or short across the pads). 3/9/2021 Introduction to Engineering Electronics K. A. Connor 17

Disposable Camera Electronics • While charging, you should hear a high pitched whine. This is the oscillator circuit. • Fire the circuit by triggering the shutter – the flash should go off. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 18

Disposable Camera Electronics • The oscillator produces a time varying voltage (sort of sinusoidal) from the 1. 5 V battery. • A time varying voltage is necessary to produce a high voltage using a transformer. • The high voltage output from the transformer is rectified using diodes to produce a high DC voltage to charge a capacitor. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 19

Disposable Camera Electronics • Once the high voltage (320 V) capacitor is charged, a small neon bulb will light up. • The charging is then stopped either manually (you stop pushing on the charge switch) or automatically. • Then when the shutter is engaged, a switch is closed which triggers the flash lamp. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 20

Disposable Camera Electronics • The flash lamp has three electrodes: § Two connected across the high voltage capacitor § One connected to a pulse transformer • The third electrode provides a short very high voltage pulse to ionize the xenon gas in the flash tube. Once the gas is ionized, it will carry current and discharge the capacitor. The current from the capacitor provides the energy for the high intensity light. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 21

Disposable Camera Electronics • This is the circuit diagram for the camera used in the lab. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 22

Disposable Camera Electronics • A transformer is used to step up or step down voltages and currents. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 23

Disposable Camera Electronics • The secondary voltage V 2 is equal to N times the primary voltage V 1. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 24

Disposable Camera Electronics • The turns ratio N is equal to the ratio of the number of secondary windings to the number of primary windings. For a step up transformer this ratio is greater than 1. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 25

Disposable Camera Electronics • You will also connect a trigger circuit in the lab to make the camera flash when light levels change. To operate the circuit, you need 5 V which is obtained from the battery using a DCDC converter. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 26

Disposable Camera Electronics • The lab circuit again 3/9/2021 Introduction to Engineering Electronics K. A. Connor 27

Disposable Camera Electronics • Note that the wires from the protoboard circuit must be soldered to the camera circuit. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 28

Disposable Camera Electronics: References • Disposable Camera Electronics from the Exploratorium • Disposable Camera Dissection from the Exploratorium • Disposable Camera Lab from the University of Washington • Dissecting Disposable Cameras for Parts 3/9/2021 Introduction to Engineering Electronics K. A. Connor 29

Soldering • • • Your TA will show you how to solder. Place parts mechanically first, if possible. Apply enough heat. Watch for cold solder joints. How to Solder Like a Pro 3/9/2021 Introduction to Engineering Electronics K. A. Connor 30

Cold Solder Joints • Note that cold solder joints tend to form ball shapes and do not make contact between wires and pc boards • Properly heated solder should flow 3/9/2021 Introduction to Engineering Electronics K. A. Connor 31

Stun Guns • Outer electrodes must come in contact with attacker. • Inner electrodes are closer together and thus can spark at the high voltages used to deter attackers. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 32

Stun Guns: What is Inside? • This is what is inside a cheap stun gun (provided by someone who likes to take things apart). 3/9/2021 Introduction to Engineering Electronics K. A. Connor 33

Stun Guns: What is Inside? • Oscillator voltage is stepped up to a fairly high voltage with a transformer. • This is used to charge a capacitor through a rectifier made with four diodes. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 34

Stun Guns: What is Inside? • When the voltage across the capacitor is high enough to spark across the gap, a short pulse is created across the primary of a pulse transformer and a large voltage pulse results. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 35

Stun Guns: What is Inside? • The spark gap is simply the two pieces of metal strip in a cross shape. A much larger spark gap was used in the can crusher discussed in lecture 6. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 36

Stun Guns: What is Inside? • The first transformer is shown at the left. • The pulse transformer is shown at the right. Note that it is potted so that it can operate at higher voltages. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 37

Tesla Coil • Nikola Tesla – The father of AC and a certifiable mad scientist, is one of the most interesting electrical scientist/engineers who has ever lived. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 38

Tesla Coil • On this and the last slide is shown a small lab scale Tesla Coil 3/9/2021 Introduction to Engineering Electronics K. A. Connor 39

Tesla Coil • The circuit has some similarities to the flash tube and stun gun. Note the two transformers and the spark gap. The resonance effect (L and C) also plays a large role in making the voltage large enough to cause sparks. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 40

Tesla Coil • This is Tesla’s Wardenclyffe Lab in Shorham Long Island where he planned to use this huge coil to transmit radio across the planet. 3/9/2021 Introduction to Engineering Electronics K. A. Connor 41

Where Will You See This Material Again? • Circuits, Electronics, Components § ECSE-2010 Electric Circuits § ECSE-2050 Analog Electronics § ECSE-2060 Digital Electronics • Transformers § ECSE-2100 Fields and Waves I • Applications of Electronics § Many classes 3/9/2021 Introduction to Engineering Electronics K. A. Connor 42