Nuts and Volts - August 2011

READER-TO-READER TECHFORUM

>>>YOUR ELECTRONICS QUESTIONS ANSWERED HERE BY N&V READERS<<<

reset button sets the display to 00. Pushing either counter button once will cause the display to count up or down once. Holding down either counter button will cause the display to continuously count up or down. Pushing the flash button will toggle the display to either flash or stay on.

Make your own display by mounting LEDs onto a piece of 12" square, 1/8" thick plastic such as McMaster 8747K112. To make the display easier to see, mount a clear, gray-tinted plastic of the same size over the LEDs, such as McMaster 85805K26.

Each segment is made up of five LEDs spaced 0.8" to 0.9" apart, center-to-center yielding 8" to 9" high digits. LCDs consume far less current, but finding the sizes you've requested can be difficult and pricey. Using LEDs lowers the cost considerably and gives you more options such as size, colors, etc. For an indoor environment, use only diffused LEDs rated about 200 mcd or less.

[#6117 - June 2011]

AC Resistance Needed

How can I find the AC resistance of the emitter diode of a power transistor?

AC resistance of the emitter diode of a transistor (re) can be calculated by: re = .026v / Ie where Ie is the DC emitter current.

This is the solution for the resistance at room temperature of 25 degrees Celsius. You can find the emitter current by measuring it directly (open the emitter lead and insert the milliammeter), indirectly, (if there is a single external emitter resistor, measure the voltage drop on the emitter resistor and use Ohms Law to find the current), or by simulation.

To simulate, download LTspice (free) and input the transistor circuit you want to use. Place your cursor over and around the emitter until you see the clamp-on ammeter icon, then left-click. The emitter current will be plotted.

Bill Bradrick Pittsburg, KS

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ADvertiser INDEX

AMATEUR RADIO AND TV McGills Warehouse .................................. 64 Ramsey Electronics, Inc. ................... 20-21 V-Module ................................................. 64

BATTERIES/CHARGERS

Cunard Associates .................................. 27

BUYING ELECTRONIC SURPLUS Jaycar Electronics .................................... 81 Weirdstuff Warehouse ............................. 27

CCD CAMERAS/VIDEO Circuit Specialists, Inc. ....................... 82-83 Ramsey Electronics, Inc. ................... 20-21

CIRCUIT BOARDS AP Circuits .............................................. 42 Cunard Associates .................................. 27 Dimension Engineering ............................ 65 ExpressPCB .............................................. 9 Front Panel Express LLC ........................ 42 PCB Pool ................................................. 18 V-Module ................................................. 64

COMPONENTS Anaren ..................................................... 25 Cana Kit Corp. ........................................ 72 Fun Gizmos ............................................. 27 Jameco .................................................... 61 Noritake ................................................... 13 V-Module ................................................. 64

COMPUTER
Hardware
Noritake ................................................... 13
Weirdstuff Warehouse ............................. 27

Microcontrollers / I/O Boards Abacom Technologies ............................... 8 Chipino .................................................... 27 Cross The Road Electronics ................... 13 Fun Gizmos ............................................. 27 I2I Controls.................................................. 7 microEngineering Labs ............................ 72

80 August 2011

MikroElektronika ........................................ 3 Parallax, Inc. .............................Back Cover Pololu Robotics & Electronics .................... 4 Solarbotics/HVW ..................................... 41

DESIGN/ENGINEERING/
REPAIR SERVICES
Cana Kit Corp. ........................................ 72
ExpressPCB .............................................. 9
Front Panel Express LLC ........................ 42
PCB Pool ................................................. 18

EDUCATION BaneBots ................................................. 41 Blue Wolf .................................................. 19 Command Productions ............................ 19 McGills Warehouse .................................. 64 NKC Electronics ...................................... 27 PAiA ......................................................... 33 Poscope ................................................... 25

EMBEDDED TOOLS I2I Controls.................................................. 7 NetBurner .................................................. 2

ENCLOSURES Front Panel Express LLC ........................ 42 Integrated Ideas & Tech. ......................... 40

KITS & PLANS Cana Kit Corp. ........................................ 72 Jaycar Electronics .................................... 81 NetBurner .................................................. 2 NKC Electronics ...................................... 27 PAiA ......................................................... 33 QKITS....................................................... 27 Ramsey Electronics, Inc. ................... 20-21 Solarbotics/HVW ..................................... 41

LEDS

LEDtronics ............................................... 33

LIGHTING

LEDtronics ............................................... 33

MISC./SURPLUS All Electronics Corp. ................................ 43 Front Panel Express LLC ........................ 42 Weirdstuff Warehouse ............................. 27

MOTORS

BaneBots ................................................. 41 Jameco .................................................... 61

OPTICS

Noritake ................................................... 13

PROGRAMMERS microEngineering Labs ............................ 72 MikroElektronika ........................................ 3

RF TRANSMI TTERS/RECEIVERS Abacom Technologies ............................... 8 Anaren ..................................................... 25 Blue Wolf .................................................. 19 Twin Peaks Robotics ............................... 27

ROBOTICS

BaneBots ................................................. 41 Blue Wolf .................................................. 19 Cross The Road Electronics ................... 13 Fun Gizmos ............................................. 27 Jameco .................................................... 61 Lemos International Co., Inc. .................. 13 Lynxmotion, Inc. ...................................... 42 Pololu Robotics & Electronics .................... 4 Solarbotics/HVW ..................................... 41 Twin Peaks Robotics ............................... 27

SATELLITE

Lemos International Co., Inc. .................. 13

TEST EQUIPMENT Circuit Specialists, Inc. ....................... 82-83 Dimension Engineering ............................ 65 Electronic Design Specialists................... 65 HAPRO Electronics .................................... 5 Jaycar Electronics .................................... 81 McGills Warehouse .................................. 64 NKC Electronics ...................................... 27

Poscope ................................................... 25

TOOLS

MikroElektronika ........................................ 3 NetBurner .................................................. 2 PanaVise ................................................. 33

WIRELESS PRODUCTS

Anaren ..................................................... 25 Cross The Road Electronics ................... 13 Twin Peaks Robotics ............................... 27

Abacom Technologies ......................... 8

All Electronics Corp. ......................... 43

Anaren .............................................. 25

AP Circuits ........................................ 42

BaneBots .......................................... 41

Blue Wolf............................................ 19

Cana Kit Corp. .................................. 72

Chipino .............................................. 27

Circuit Specialists, Inc. ................ 82-83

Command Productions ..................... 19

Cross The Road Electronics ............. 13

Cunard Associates ............................ 27

Dimension Engineering...................... 65

Electronic Design Specialists............. 65

ExpressPCB ........................................ 9

Front Panel Express LLC ................. 42

Fun Gizmos ...................................... 27

HAPRO Electronics.............................. 5

I2I Controls............................................ 7

Integrated Ideas & Tech. ................... 40

Jameco ............................................. 61

Jaycar Electronics.............................. 81

LEDtronics ........................................ 33

Lemos International Co., Inc. ............ 13

Lynxmotion, Inc. ................................ 42 McGills Warehouse............................ 64 microEngineering Labs ...................... 72 MikroElektronika ................................. 3 NetBurner ............................................ 2 NKC Electronics ................................ 27 Noritake ............................................. 13 PAiA .................................................. 33 PanaVise ........................................... 33 Parallax, Inc. ......................Back Cover PCB Pool .......................................... 18 Pololu Robotics & Electronics.............. 4 Poscope ............................................. 25 QKI TS ................................................ 27 Ramsey Electronics, Inc. ............. 20-21 Solarbotics/HVW ............................... 41 Twin Peaks Robotics ........................ 27 V-Module ........................................... 64 Weirdstuff Warehouse ...................... 27

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