1. Lecture 1: Safety and Protection

2. 1. A robot may not injure a human being or, through inaction, allow a human being to come to harm. 2. A robot must obey the orders given to it by human beings, except where such orders would conflict with the First Law. 3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws. >> Isaac Asimov <<

3.  NEVER WORK HOT!  All Design Work must account for Human Exposure to Electric Hazards (Idiot-Proof)

4.  Safe Design Practices include:  Enclosing Electrical Components to avoid incidental human contact  Providing a Discharge Path for all Capacitors  Design for discharge to under 5V in 2 seconds

5.  Design for Environment  Internal Cooling/Heating (entire exterior must be “touchable”)  Weatherproofing  Hazardous Materials/Containment  Battery Acid  Lead  Oil Peltier Devices – Exploit the Thermoelectric Effect to convert a temperature differential into an electric voltage (Reversible!) Source: commons.wikimedia.org

6.  Kill Switches  Must completely De-Energize Project  If your project is mobile, it will require a Local Kill Switch (Big RED Button, Easily Accessible) Source: Cartek

7.  A remote Kill Switch could act via one of many “wireless” technologies: Infra-Red, AM Radio, FM Radio, IEEE 802.11g, Bluetooth, etc.  Range and Noise will be issues in the Contest Environment  Example: http://www.kitsrus.com/pdf/k180.pdf http://www.kitsrus.com/pdf/k180.pdf  UHF Radio  2-Channel (Control 2 things)  Relay Backend (Heavy Duty)

8.  Grounding too often an ‘Afterthought”  Soild, Reliable Ground Plane eliminates many Noise and Reliability Problems  Ground Plane on Mobile Platform cannot reliably be joined to Earth Ground. (Floating with Respect to Earth) Induced Voltages on Vehicle must be considered when designing and maintaining Vehicle

9.  Good Example of Terminating a Ground Wire (or any wire) – Be aware of Vibration!

10.  Proper Termination of Shielded Cable

11.  In the case where a low power analog signal (such as from a radio antenna) requires a ground plane, AVOID direct connection to a ground plane used for digital equipment (Noisy).  In the absence of Earth Ground, establish an Analog Ground Plane and a Digital Ground Plane and connect the two with a resistive path to attenuate noise.

12.  Electrical Circuits Require Protection against Fault, Failure or Improper Use  Always Know the Failure Modes of Equipment used in your Design (e.g. A Diode can fail short)  Types of Circuit Protection:  Over Current  Over/Under Voltage  Over Heating  Over/Under Frequency (AC Systems)

13.  Since most circuit designs assume established voltage levels within the circuit, regulating current will regulate the power in the circuit.  Conductors must be sized to handle the maximum load current and any transient short-circuit current level available.  Example: NEC indicates 14 Gauge Solid Copper will safely carry 15 Amps when properly protected by a circuit breaker  Know When to Use Solid Wire and When to Use Braided Wire

14.  Circuit Breaker – Rated for a maximum application voltage, interrupting level and maximum interrupting current (or volt-amps)

15.  Fuses  Inexpensive Over Current Protection  One – Shot  Fast or Slow  Be Aware of resistance

16.  Self-Resetting Fuses  Thermistor that is conductive at room temperature  If current exceeds rating, heats up and becomes non- conductive  Conductive again after cooling down Source: commons.wikimedia.org

17.  It is often desirable, especially in power electronics, to limit transient over-voltages in a circuit  Zener Diodes are an inexpensive means of limiting low-power over-voltages  MOV (Metal-Oxide Varistor) Surge Suppressors provide a heavier duty solution

18.  IMPORTANT to electrically isolate delicate electronics from power circuits (Pulse Width Modulation motor drives, etc)

19.  Provide Electric Isolation (energy transfer is through magnetic circuit in core)  AC Signals ONLY

20.  Provide Electric Isolation (magnetic circuit)  Provide “electro-mechanical Amplification”  Low Power Signal Controls Large Power Circuit  AC or DC  Not for Repetitive Operations

21.  Provide Electric Isolation (Energy Transfer via Photons)  Many Types of Output: BJT, Darlington Pair, SCR, etc

22.  Enable Pin = 0 puts driver in High Impedance State (Open Circuit A to B)  High Input Z, Low Output Z (10 GE output)  Non-Inverting or Inverting