1. BE Lesson 6: Make an access alarm What is a diode? What is an SCR? Make an access alarm. © 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012

2. The electrical engineer’s “conventional current” + - DC Amps + _ assumed direction of current direction of electron flow

3. BE demo 6-1. What’s a check valve? How is a diode like a check valve? [Adapted from Building Power Supplies, Master Publishing Inc, David Lines, 1991] EASY FLOW GATE OPEN CHECK VALVE (easy flow direction) + - VfVf Anode Cathode GATE CLOSED FLOW BLOCKED CHECK VALVE (no flow direction) - + VfVf Anode Cathode Forward biased diode: Large current for (+) directed voltage Reverse biased diode: No current for (-) directed voltages

4. How does a diode operate in a circuit? + Forward voltage drop ~ 0.7 volts Maximum reverse voltage = 50 volts Adapted from http://www.kpsec.freeuk.com/components/diode.htm -

5. BE ckt 6-2. How does a diode work? +  v 220  LED +  v 220  LED i ~ 30 ma i ~ 0 ma Ckt 6-1 (A) (LED on) (+) (-) (+) (-) Ckt 6-1 (B) (LED off) Forward biased diode Reverse biased diode (+) (-)

6. Hook up diagram for BE ckt 6-2A. Diode 1N4001 is forward biased. (LED is on.) 1N4001 220 + 9.0 volts

7. Hook up diagram for BE ckt 6-2B. Diode 1N4001 is reverse biased. (LED is off.) 1N4001 220 + 9.0 volts

8. BE ckt 6-3. Access Alarm Circuit +  v 220  LED (+) (-) SCR (2N5061) A C G NO 6.8 K  S1 S2 NC C1 0.1  F Adapted from Electronic Kourseware Interactive, Discover Electronics, www.eki.com

9. BE ckt 6-3. Hookup diagram. 220 SCR 2N5061 (face points up) G A C NC switch - push to open + 9.0 volts 0.1  F (n.p.) 6.8K NO switch - push to close S1 S2

10. BE ckt 6-4. Access Alarm with buzzer +  v 220  LED (+) (-) SCR (2N5061) A C G NO 6.8 K  S1 S2 C1 0.1  F Adapted from Electronic Kourseware Interactive, Discover Electronics, www.eki.com buzzer 220  NC

11. BE ckt 6-4. Hookup diagram. 220 SCR 2N5061 (face points up) G A C NC switch - push to open + 9.0 volts 0.1  F (n.p.) 6.8K buzzer 220 NO switch - push to close