Nuts & Volts - February 2006

PARTS LIST

(Listed are the parts in the Geller Labs kit; most recommended parts can be substituted with any same-valued part from your junk box.)

ITEM QTY VALUE DESCRIPTION

❑ 1 2 0.1μF Ceramic, CKO6, 10%, 100V, or equivalent

Mouser CK06BX104K

❑ 2 2 C2, 3 0.1μF Panasonic film, ECQ-V1H104JL

Digi-Key P4525-ND, or equivalent

❑ 3 1 U1 LM399H 7V ovenized reference diode,

National Semiconductor

Digi-Key LM399H-ND

❑ 4 1 U2 LM6132BIN National Semiconductor,

Digi-Key LM6132BIN-ND

❑ 5 1 1% metal film, 1/2W (Mouser)

❑ 6 1 1% metal film, Xicon 1/4W (Mouser)

❑ 7 1 1% metal film, Xicon 1/4W (Mouser)

❑ 8 2 1% metal film, Xicon 1/4W (Mouser)

For ex: Mouser ME271-7.5K

❑ 9 1 R7 5K Bourns 3329H trimpot

Mouser 652-3329H-1-502

❑ 10 1 R8 4.64K 1% metal film, Xicon 1/4W (Mouser)

❑ 11 1 IC socket Mill-Max DIP Low Profile

Mouser: 575-193308

❑ 12 1 PCB Geller Labs www.gellerlabs.com MGTA PCB

Kit of all parts (no documentation, no enclosure) Geller Labs MGTA KIT (go to website)

REFERENCE C1, 4

R1

R5

R2

R3, 4, 6

100 10K 3.24K 7.5K

ranging from near 0.2V to 14V full scale. For a TI OPA2277 or an Analog Devices OP-297 dual op-amp, the range is about 2.5V to 13V. See the sidebar for more information on op-amp rail-to-rail performance. Note that C5 is available for especially noisy environments. It can be an additional ceramic capacitor or a tantalum or electrolytic capacitor (observe polarity!). Best operation is achieved with a 15V linear power supply, but a switcher should be okay too if C5 is installed.

Ideas for Future Expansion

The applications sidebar shows some ideas for different uses. Many experiments can be done to further characterize the project. For example, measure how changes in absolute temperature change the output voltage independent of the wind. Or, you can calibrate the board against known air speeds to determine an absolute calibration or the linearity of the output over a range of low velocity wind speeds. A small muffin fan can be used at different voltages to create variable breezes for calibration experiments. Some fans create a lower, less concentrated breeze on the intake side. Another factor to investigate is how the LM399 oven currents vary with time and to determine if LM399 oven life is reduced by running it at elevated heater currents for long periods of time in a continuous breeze.

As a closing note, I need to mention that I filed a patent application regarding the use of ovenized reference diodes as sensors in thermal anemometers. If a patent issues, I will grant free licenses to individuals for use in hobby and amateur science experiments (but not for commercial use or sales including multiple hobby sales).