SmartArt - AD405 - Drew Browning

POWERED DIGITAL OUTPUT - the simplest output transducer is the LED because it can be connected directly to the microcontroller or other TTL logic levels. A microcontroller output can supply .20ma typically, which is enough to light an LED. The LED is one of the most important components when working in physical computing because in addition to being a very low power device it is used as a general-purpose indicator, helping to debug and inform us of the state of a circuit. When we can turn an LED on and off under program control we know we can turn just about any other electrical device or transducer on and off, including incandescent lights, motors, speakers, heaters, etc. To do so we need a way to control the higher power requirements of these devices. Two common components to switch higher voltage and amperage are the relay and transistor.

RELAY: an electromechanical switch or solid state for AC loads only

Reed Relay – coil 5V@20mA Solid State Relay -

TRANSISTOR: a semiconductor used for switching or amplifying

TO-92 TO-220 TO-3

2N2222 NPN Transistor - General-purpose silicon, high-speed, medium control switching transistors. Rated 600mW, Case Type TO-92

TIP120 NPN-D Transistor - Power dissipation of 80W, Case Type TO-220

2N3055 NPN Transistor - Power dissipation of 115W. Case Type:TO-3

NPN can be used like normally open switches.

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Relay Drivers: used for relay coil circuits requiring greater power than the microcontroller can provide.

If input = 5V @ .002 mA then R=2.2Kohm Use this circuit if input voltage and coil voltage are them same

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Transistor Switching Circuit: controlling multiple LEDs and incandescent lamps

- LEDs in Series – the current is the same as one LED but the forward threshold voltage is 2V per LED

- 3 LEDs in series requires 6V to light

Incandescent Lamp Driver – use TIP120 NPN-D Transistor - Power dissipation of 80W, Case Type TO-220