Do-It-Yourself Diodes · PDF fileDo-It-Yourself Diodes ... Galena? Backwards polarity Whatever...
Transcript of Do-It-Yourself Diodes · PDF fileDo-It-Yourself Diodes ... Galena? Backwards polarity Whatever...
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1•33
Do-It-Yourself Diodes
Society for Amateur ScientistsNational Citizen Science Conference
August 2006
Ed Nisley - [email protected]
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2•33
Coming Attractions
Radio Rocks
EZ Curve Tracer
Radio Circuit Model
Mineral Diodes & Thingies
Rust Never Sleeps
Why Diodes Matter
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3•33
In The Beginning
Before integrated circuits...
Before transistors...
Before vacuum tubes...
Before electronics...
... there were radios!
Modern radio by VE6AB
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The Simplest Possible Radio
Antenna
Ground
Earphone
Detector
AM demodulator (huh?)
A rock on a hard place
Crystal diode!
Tuning? Hah!
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Mineral Samples
Who knew?
Nobody!
Conflicting stories
Try all combinations
Most don’t work at all
How can you tell?
Instrumentation!
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6•33
The Big Idea
Jam current (I) in
How much?
Polarity?
Measure volts (V) across
Range?
Plot results: curves!
It can be done manually
More fun automatically
Oscilloscope screen shots
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7•33
The Little Details
Triangle wave input
200 Hz, 8 V peak
Voltage to Current
Oscilloscope X axis
Measure V at sample
Differential to single
Oscilloscope Y axis
±10 mA and ±10 V
Still makes sparks…
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8•33
Enlarged to Show Texture
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Cat’s Whisker Probe
Mineral in metal pot
Wire pin-point probe
Steel? Bronze? Carbon?
3-axis ball slide mount
Springy thing
Patience
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10•33
He Who Dies With The Most Stuff...
3-axis positioner
0.001” resolution
0.5” accessible cube
Zero backlash
Black-belt dweebdom
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11•33
Probe and Sample Holder
Telescoping brass tubes
Tapered clock pins
Springy thing
EMT fitting
Gratuitous CNC
Low frequency = clips
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12•33
Sample Holder
Wood’s Metal
Makes solid contact
But: Pb+Cd+Bi+Sn
But: melts at 160° F
Use Field’s Metal?
Friction-fit probe tips
Steel, bronze, carbon
Small differences?
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13•33
Calibration – 1 kΩ Resistor
1 V input = 1 mA
Scope Axes
X = current (2 mA/div)
Y = voltage (2 V/div)
Linear!
Whew…
Set DC offset = 0
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14•33
Calibration – 1N914
Jellybean Si diode
Vfwd
= 0.5 V
Pretty close
Irev
= zilch
Limited by diff amp’s input resistance
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15•33
Iron Pyrite
Green trace
Nearly a resistor
Red trace
More like a diode
Blue trace
Both better & worse
Same lump!
Probe material?
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16•33
Spice Circuit Model
Diode = switch
Voltage controlled
Maybe a lousy switch
Resistance from plots
R = ΔV /Δ I = slope
C1 & R2 ≈ earphone
High impedance
V1*V2 = AM signal!
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17•33
AM Demodulation
Low voltage RF
This is before tubes!
Poor diodes are OK
Green ≈ 3.6 / 1 (rev/fwd)
Red ≈ 5.6 / 1
Modern diodes are NG
Purple = Schottky ≈ ∞ / 1
But Vfwd
still too high
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18•33
Iron Pyrite
Huh?
Sorta Zener-ish
Marginal diode
For low I & V, anyway
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Lead - Galena?
Backwards polarity
Whatever that means
Low Vfwd
Bronze probe
Best of a bad sample
Who knew?
Maybe it’s just lead?
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Chalcopyrite
Say kal’•keh•pie’•right
Looks diode-ish
If you squint
Low Vfwd
But wait...
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21•33
Chalcopyrite
It’s a Diac!
Bilateral trigger diode
It’s a resistor!
For very low I
Negative resistance
Current ↑ = Voltage ↓
Note scale change
5 V and 5 mA / div
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22•33
Galvanized Steel
Propane torch
Little black spots…
Do this outdoors!
Iron-tin-zinc alloy?
Cadmium? Ick!
Looks like high R
And not a diode
But wait…
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Galvanized Steel Bestiary
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Rust Never Sleeps
Ordinary steel bolt
Salt + towel + copper
Cu + Fe = 650 mV
At only 1 mA
Slow and steady
AA cell
1500 mV & 10 mA
4 hours later…
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25•33
Steel Corrosion
Nonlinear
Symmetric
Sorta, kinda
Negative resistance
Oscillator!
No Battery Needed
Self-biasing circuitry
DC bias + small AC
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26•33
Linear Mixing Circuit
Linear mixing
Only “resistors”
Sum of amplitudes
No surprises
Ohm’s Law, etc
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Linear Mixing Results
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28•33
Nonlinear Mixing Circuit
Nonlinear mixing
Usually a diode, but …
Any nonlinearity will do
± nF1 ± mF
2
Amplitudes? Hah!
No analytic equations
Simulation values?
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29•33
Nonlinear Mixing Result
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30•33
RF vs. The Rusty Bolt
Mountaintop radio
Many transmitters
High RF field intensity
Sensitive receivers
Galvanized towers
Acid rain
Corrosion
Intermodulation!
±nF1±mF
2±pF
3± … Mt Beacon NY - Photo by WB2UWU
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31•33
DIY Diodes
They’re everywhere
They’re cheap
OK, not that positioner
They’re easy, sorta
You’ll learn…
… about electronics
… about patience
Demo: Sunday AM!!
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32•33
References
My column in Circuit Cellar magazine: www.circuitcellar.comOctober 2006 is mostly this talk, has file of scripts, pictures, other stuff February & April 2003 describe nonlinear frequency mixing
Semiconductor curve tracer using PC sound card: George Steber, WB9LVICircuit Cellar, Jan 2004ARRL QEX, July 2006: http://www.arrl.org/qex/2006/07/qx7steber.pdf
Good overview of crystal-set parameters: http://www.oldradioworld.de/gollum/analysis.htm
Zinc negative resistance oscillators: http://home.earthlink.net/~lenyr/zincosc.htm
Galvanic Series table: http://www.ocean.udel.edu/seagrant/publications/corrosion.html
Wood’s metal, springs, phosphor bronze sheet, tools from MicroMark: http://micromark.com/
Taper pins and small parts from S. LaRose, Inc: http://www.slarose.com/ (dead on 18 Aug 06)
Capturing oscilloscope traces with Kermit: http://www.columbia.edu/kermit/index.html
Converting HPGL to bitmaps with hp2xx utility: http://www.gnu.org/software/hp2xx/
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33•33
Who Am I?
Ed Nisley
Say “NISS-lee”, even though my ancestors were half-essed
Engineer, author, tinker, family guy
Circuit Cellar: Above the Ground Plane - www.circuitcellar.com
Analog & RF stuff
Dr Dobb’s Journal: Nisley’s Notebook - www.ddj.com
Embedded systems & hardware stuff
Sept 62