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Archive for December, 2012

Monthly Subconscious: Was Floater Ever Secure

Was Floater Ever Secure

Was Floater Ever Secure

The collection of refrigerator words went off to college for the amusement and edification of our Larval Engineer’s compadres. These magnetic words emerged from nooks and crannies on and around the refrigerator over the next few months and form what must be the Ultimate Message from the Subconscious:

Perhaps it’s an admonition to would-be Airship Pirates?

In text:

was floater ever secure or will praise drive pilot

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Poster-izing PDFs

For reasons best left to the imagination, we needed some large signs for the front yard. I must look this up every time I do it, so here’s the process…

  • Create document in LibreOffice (or whatever), save as PDF
  • Convert PDF to EPS = Encapsulated Postscript
  • Apply poster to enlarge & paginate
  • Convert PS to PDF for ease of printing

Bash does the heavy lifting, after you install whatever packages your Linux distro may not have included:

pdftops -eps OnePage.pdf PosterPage.ps
poster -v -m Letter -p20x28i -o PosterMulti.ps PosterPage.ps
ps2pdf PosterMulti.ps

Then it’s a simple matter of a cutting mat, a razor knife, a glue stick, and some tape…

Memo to Self: Align the lower row along the hardwood floor planks!

2 Comments

Master Combination Padlock: Cracking Thereof

A Master Combination Lock emerged in locked condition from a box o’ stuff I handled during Mad Phil’s Great Cleanout. It’s not the highest security lock you’ll ever meet; about 15 minutes of fiddling produces the desired result:

Master Combo Padlock - opened

Master Combo Padlock – opened

A bit of searching suggests it’s similar to the Master No. 1523D Combination Padlock, although this one came in pink. The doc describes how to change the combination:

  • Unlock (or crack) the lock
  • Pull off the spring-loaded endcap (I had to pry with a screwdriver)
  • Slide off the combination wheels
  • Reinstall in desired orientation

After removing the cap and wheels, it looks like this:

Master Combo Padlock - wheels off

Master Combo Padlock – wheels off

Each wheel fits onto a rotating metal disk and engages three teeth, one of which has a notch. Align all four notches with the Master logo / index line and the lock opens:

Master Combo Padlock - dial alignment marks

Master Combo Padlock – dial alignment marks

Given just that picture, I think you can figure out how to get past one of these in a hurry. Right?

4 Comments

LED Stress Tester: First Light!

Based on that circuit simulation, the LED Stress Tester schematic looks about like you’d expect:

LED Stress Tester Schematic - updated

LED Stress Tester Schematic – updated

[Update: Left out the Schottky diode that makes the 20% duty cycle actually work. Drat & similar remarks.]

The manual wiring turned into a hairball, but from the top it looks pretty good:

LED Stress Tester - red and amber LEDs

LED Stress Tester – red and amber LEDs

The 20 pin DIP IC sockets provide spare contacts, so that ruining a few by jamming fat LED leads into them won’t be a tragedy. Each LED string uses one of three adjacent contacts, which left room for a fourth string of amber LEDs that are, even to the naked eyeball, nearly indistinguishable from the red LEDs.

The 555 timer output waveform looks just like the simulation:

Timer Waveform

Timer Waveform

The trimpots sit near the middle of their rotations, which is always comforting. The duty cycle trimpot can’t quite get down to 1 ms, which doesn’t matter right now.

This scope shot shows the total forward drop across the three LED strings, with V=0 offset way down below the bottom of the display:

Red LED - group Vf

Red LED – group Vf

That voltage includes the IRLZ14 MOSFET drain-source voltage, which amounts to a bit less than the thickness of the fuzz on the traces. In round numbers:

VDS = 400 mA x 0.100 mΩ = 40 mV

That’s based on this measurement from the MOSFET tester a while back:

IRLZ14 detail

IRLZ14 detail

You could argue the drain voltage is closer to 60 mV. I’d argue that the overall accuracy of all these measurements leaves a lot to be desired; we’re in the right ballpark no matter what.

Anyhow.

From the top, the three traces show LED groups 7-9, 1-3, and 4-6 in exactly the predicted order (1-3: 6.445, 4-6: 6.372, and 7-9:6.469 V), if not with exactly the predicted absolute voltages.

Part of the reason may be that the current limiting resistors that produced about 100 mA were 5.6 Ω, rather than the predicted 10 Ω, They actually measure about 5.7 Ω and the forward drop (from that scope shot) is around 750 mV, so the current could be up around 130 mA: a bit hot. I want to measure the current more closely before leaping to any conclusions.

The 1/4 W ballast resistors dissipate 100 mW peak / 20 mW average and each LED dissipates 300 mW peak and 60 mW average.

The 7.5 V wall wart I planned to use requires a much higher average load for good regulation (it emits 10.5 V for light loads), so this lashup runs from that 2 A bench supply through the other end of the Tek banana cable I hacked apart to make those SMD tweezers. The supply voltage at the coaxial jack drops by about 120 mV during the pulse, but we’re dealing with measurements up from ground.

I think the exponential curve in that scope shot shows the LED internal temperature rise during the pulse. If you figure -2 mV/°C (based on the ever-reliable and always accurate Wikipedia), then the 150 mV change along the exponential works out to 50 mV per LED and a 25 °C temperature rise. I have no idea whether thermal-cycling the LEDs at 100 Hz will cause early bond wire failure or not, which is why I want to let this run for a month or so.

I love it when a plan comes together…

2 Comments

Amber LEDs: Current vs. Voltage

While wiring up the LED stress tester, I realized I should abuse a string of amber LEDs along with the three red strings. Herewith, four amber LEDs from the top of their bag, with LED 5 = LED 1 retested:

Amber LEDs - 100 mA

Amber LEDs – 100 mA

Apart from being an outlier, that red trace seems much prettier than the others, doesn’t it?

The data file:

# LED Curve Tracer
# Ed Nisley - KE4ZNU - December 2012
# VCC at LED: 4872 mV
# Bandgap reference voltage: 1039 mV

# Insert LED, press button 1 to start...
# INOM    ILED    VccLED    VD    VLED    VG    VS    VGS    VDS    <--- LED 1
0    0    4872    3668    1203    0    0    0    3668
10    10087    4872    2951    1920    2079    105    1973    2845
20    19716    4872    2898    1973    2257    207    2050    2691
30    30262    4872    2864    2007    2416    317    2099    2546
40    39891    4872    2840    2031    2551    418    2132    2421
50    49520    4872    2821    2050    2686    519    2166    2301
60    59607    4872    2806    2065    2811    625    2185    2180
70    69694    4872    2792    2079    2927    731    2195    2060
80    79782    4872    2777    2094    3061    837    2224    1940
90    90328    4872    2768    2103    3206    948    2257    1819
100    99957    4867    2763    2103    3307    1049    2257    1713

# Insert LED, press button 1 to start...
# INOM    ILED    VccLED    VD    VLED    VG    VS    VGS    VDS    <--- LED 2
0    0    4872    3991    881    0    0    0    3991
10    9628    4872    2946    1925    2084    101    1983    2845
20    20174    4872    2888    1983    2257    211    2046    2676
30    30262    4872    2850    2022    2416    317    2099    2532
40    39891    4872    2826    2046    2551    418    2132    2407
50    49978    4872    2802    2070    2681    524    2156    2277
60    60066    4872    2782    2089    2811    630    2180    2152
70    69694    4872    2768    2103    2936    731    2205    2036
80    79782    4872    2753    2118    3076    837    2238    1916
90    89869    4872    2744    2127    3177    943    2233    1800
100    99957    4872    2739    2132    3297    1049    2248    1689

# Insert LED, press button 1 to start...
# INOM    ILED    VccLED    VD    VLED    VG    VS    VGS    VDS    <--- LED 3
0    0    4872    3788    1083    0    0    0    3788
10    9628    4872    2941    1930    2084    101    1983    2840
20    19716    4872    2888    1983    2262    207    2055    2681
30    29803    4872    2850    2022    2412    312    2099    2537
40    39891    4872    2826    2046    2551    418    2132    2407
50    49978    4872    2806    2065    2681    524    2156    2282
60    60066    4872    2787    2084    2811    630    2180    2156
70    70153    4872    2777    2094    2960    736    2224    2041
80    80240    4872    2768    2103    3061    842    2219    1925
90    90328    4872    2753    2118    3182    948    2233    1805
100    99957    4867    2753    2113    3302    1049    2253    1704

# Insert LED, press button 1 to start...
# INOM    ILED    VccLED    VD    VLED    VG    VS    VGS    VDS    <--- LED 4
0    0    4872    3899    972    0    0    0    3899
10    9628    4872    2936    1935    2084    101    1983    2835
20    19716    4872    2888    1983    2262    207    2055    2681
30    29803    4872    2854    2017    2412    312    2099    2542
40    39891    4872    2835    2036    2551    418    2132    2416
50    49978    4872    2816    2055    2681    524    2156    2291
60    60066    4872    2797    2075    2816    630    2185    2166
70    70153    4872    2787    2084    2927    736    2190    2050
80    80240    4872    2773    2099    3061    842    2219    1930
90    90328    4867    2768    2099    3196    948    2248    1819
100    99957    4872    2758    2113    3331    1049    2282    1709

# Insert LED, press button 1 to start...
# INOM    ILED    VccLED    VD    VLED    VG    VS    VGS    VDS    <--- LED 5
0    0    4872    3841    1030    0    0    0    3841
10    10087    4872    2951    1920    2079    105    1973    2845
20    20174    4872    2907    1964    2257    211    2046    2696
30    30262    4872    2869    2002    2412    317    2094    2551
40    39891    4872    2845    2026    2551    418    2132    2426
50    50437    4872    2826    2046    2686    529    2156    2296
60    60066    4872    2806    2065    2821    630    2190    2176
70    69694    4872    2797    2075    2941    731    2209    2065
80    80240    4872    2782    2089    3076    842    2233    1940
90    89869    4872    2773    2099    3177    943    2233    1829
100    99957    4872    2763    2108    3321    1049    2272    1713

# Insert LED, press button 1 to start...

The Bash / Gnuplot routine that produced the graph has a few tweaks:

#!/bin/sh
numLEDs=4
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
base="${1%.*}"
echo Base name: ${base}
ofile=${base}.png
echo Input file: $1
echo Output file: ${ofile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "${base}"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set xlabel "Forward Voltage - V"
set format x "%6.3f"
set xrange [1.8:2.2]
#set xtics 0,5
set mxtics 2
#set logscale y
#set ytics nomirror autofreq
set ylabel "Current - mA"
set format y "%4.0f"
set yrange [0:120]
set mytics 2
#set y2label "right side variable"
#set y2tics nomirror autofreq 2
#set format y2 "%3.0f"
#set y2range [0:200]
#set y2tics 32
#set rmargin 9
set datafile separator "\t"
set label 1 "LED 1 = LED $((numLEDs + 1))" at 2.100,110 right font "arialbd,18"
set arrow from 2.100,110 to 2.105,103 lt 1 lw 2 lc 0
plot	\
    "$1" index 0:$((numLEDs - 1)) using (\$5/1000):(\$2/1000):(column(-2)) with linespoints lw 2 lc variable,\
    "$1" index $numLEDs using (\$5/1000):(\$2/1000) with linespoints lw 2 lc 0
EOF

,

1 Comment

Red LEDs: Current vs. Voltage Sorting

Running ten random red LEDs (taken from the bag of 100 sent halfway around the planet) through the LED Curver Tracer produces this plot:

Red LEDs - 80 mA

Red LEDs – 80 mA

The two gray traces both come from LED 1 to verify that the process produces the same answer for the same LED. It does, pretty much.

Repeating that with the same LEDs in the same order, but stepping 10 mA up to 100 mA produces a similar plot:

Red LEDs - 100 mA

Red LEDs – 100 mA

The voltage quantization comes from the Arduino’s 5 mV ADC resolution (the readings are averaged, but there’s actually not much noise) and the current quantization comes from the step value in the measurement loop (5 mA in the first plot, 10 mA in the second). Seeing the LEDs line up mostly the same way at 80 mA in both graphs is comforting, as it suggests the measurement results aren’t completely random numbers.

Apply this bit of Bash-fu to the dataset file:

seq 1 11 > /tmp/seq.txt ; grep -E "^100" Red\ LEDs\ -\ 100\ mA.csv | cut -f 2,5 | paste /tmp/seq.txt - > "Red LED Vf at 100 mA.csv"

Produces a numbered listing of the LED current (in μA) and voltage (in mV) at a nominal 100 mA for each LED:

1	100415	2108
2	100415	2185
3	99957	2152
4	100415	2132
5	99957	2137
6	99957	2103
7	99957	2161
8	99957	2137
9	100415	2171
10	100415	2132
11	100415	2113

Putting three red LEDs in series could produce a total forward drop anywhere between 6.309 V (3*2.103) and 6.555 V (3*2.185), a difference of nigh onto a quarter volt, if you assume this group spans the entire range of voltages and the whole collection has many duplicate values and you’re remarkably unlucky while picking LEDs. For this particular set, however, summing three successive groups of three produces 6.445, 6.372, and 6.469 V, for a spread of just under 100 mV. That suggests it’s probably not worthwhile to select LEDs for forward voltage within each series group of three, although matching parallel LEDs makes a lot of sense. I have no confidence the values will remain stable over power-on hours / thermal cycling / current stress.

The capacity plot for the Wouxun KG-UV3D lithium battery packs shows that there’s not a lot of capacity left after 7.0 V, so shutting down or scaling back to lower current wouldn’t be a major loss. However, it’s not clear a fixed resistor will do a sufficient job of current limiting with 6.5 V forward voltage across the LED string:

  • At 7.5 V, 100 mA calls for 10 Ω (drop 1 V at 100 mA)
  • At 8.2 V, 10 Ω produces 170 mA (1.7 V across 10 Ω)
  • At 7.0 V, 10 Ω produces 50 mA (0.5 V across 10 Ω)

Obviously, 170 mA is way too much, even by my lax standards.

A 100 mV variation in forward voltage between stacks, each with a 10 Ω resistor, translates into about 10 mA difference in current. This may actually call for current sensors and direct current control, although using a sensor per string, seems excessive. Low dropout regulators in current-source mode might suffice, but that still seems messy.

The test rig will run from a hard 7.5 V supply, which means I can use fixed resistors and be done with it.

The raw data behind those graphs, with LED 1 and LED 11 being the same LED:

# LED Curve Tracer
# Ed Nisley - KE4ZNU - December 2012
# VCC at LED: 4877 mV
# Bandgap reference voltage: 1039 mV

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 1
0	0	4877	3707	1169	0	0	0	3707
10	10087	4877	2970	1906	2084	105	1978	2864
20	20174	4872	2907	1964	2262	211	2050	2696
30	29803	4877	2869	2007	2412	312	2099	2556
40	39891	4877	2840	2036	2546	418	2127	2421
50	49978	4872	2821	2050	2681	524	2156	2296
60	60066	4877	2806	2070	2816	630	2185	2176
70	69694	4872	2792	2079	2927	731	2195	2060
80	80240	4877	2777	2099	3071	842	2229	1935
90	89869	4872	2768	2103	3196	943	2253	1824
100	100415	4872	2763	2108	3312	1054	2257	1709

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 2
0	0	4877	3803	1073	0	0	0	3803
10	9628	4872	2960	1911	2084	101	1983	2859
20	19716	4877	2898	1978	2257	207	2050	2691
30	30262	4877	2850	2026	2421	317	2103	2532
40	39891	4877	2816	2060	2551	418	2132	2397
50	49978	4872	2787	2084	2686	524	2161	2262
60	60066	4872	2763	2108	2816	630	2185	2132
70	69694	4872	2744	2127	2927	731	2195	2012
80	79782	4872	2729	2142	3052	837	2214	1892
90	90328	4872	2700	2171	3191	948	2243	1752
100	100415	4872	2686	2185	3331	1054	2277	1632

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 3
0	0	4877	3716	1160	0	0	0	3716
10	10087	4877	2960	1916	2094	105	1988	2854
20	19716	4877	2893	1983	2257	207	2050	2686
30	30262	4877	2850	2026	2416	317	2099	2532
40	39891	4872	2821	2050	2546	418	2127	2402
50	49520	4872	2797	2075	2681	519	2161	2277
60	59607	4872	2782	2089	2802	625	2176	2156
70	70153	4877	2763	2113	2932	736	2195	2026
80	79782	4872	2749	2123	3076	837	2238	1911
90	90328	4872	2734	2137	3182	948	2233	1786
100	99957	4872	2720	2152	3321	1049	2272	1670

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 4
0	0	4877	3716	1160	0	0	0	3716
10	10087	4877	2965	1911	2079	105	1973	2859
20	19716	4872	2903	1969	2253	207	2046	2696
30	30262	4877	2859	2017	2407	317	2089	2542
40	39891	4877	2830	2046	2546	418	2127	2412
50	49520	4877	2806	2070	2686	519	2166	2286
60	60066	4872	2787	2084	2821	630	2190	2156
70	69694	4872	2773	2099	2927	731	2195	2041
80	79782	4872	2763	2108	3052	837	2214	1925
90	90328	4872	2749	2123	3196	948	2248	1800
100	100415	4872	2739	2132	3331	1054	2277	1685

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 5
0	0	4877	3697	1179	0	0	0	3697
10	10087	4877	2965	1911	2079	105	1973	2859
20	20174	4877	2898	1978	2257	211	2046	2686
30	30262	4877	2854	2022	2412	317	2094	2537
40	39891	4872	2830	2041	2551	418	2132	2412
50	49520	4872	2802	2070	2681	519	2161	2282
60	60066	4877	2787	2089	2816	630	2185	2156
70	70153	4872	2768	2103	2932	736	2195	2031
80	79782	4872	2758	2113	3071	837	2233	1920
90	89869	4872	2744	2127	3177	943	2233	1800
100	99957	4872	2734	2137	3293	1049	2243	1685

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 6
0	0	4877	3764	1112	0	0	0	3764
10	9628	4877	2980	1896	2079	101	1978	2879
20	20174	4877	2922	1954	2262	211	2050	2710
30	30262	4877	2883	1993	2412	317	2094	2566
40	39891	4872	2859	2012	2551	418	2132	2440
50	50437	4872	2835	2036	2686	529	2156	2306
60	60066	4872	2821	2050	2816	630	2185	2190
70	69694	4872	2802	2070	2941	731	2209	2070
80	79782	4872	2787	2084	3081	837	2243	1949
90	90328	4872	2773	2099	3191	948	2243	1824
100	99957	4872	2768	2103	3307	1049	2257	1718

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 7
0	0	4877	3870	1006	0	0	0	3870
10	10087	4877	2970	1906	2089	105	1983	2864
20	20174	4877	2907	1969	2262	211	2050	2696
30	30262	4872	2859	2012	2412	317	2094	2542
40	39891	4872	2830	2041	2551	418	2132	2412
50	49978	4872	2802	2070	2686	524	2161	2277
60	60066	4872	2777	2094	2821	630	2190	2147
70	69694	4872	2758	2113	2927	731	2195	2026
80	79782	4872	2744	2127	3052	837	2214	1906
90	90328	4872	2724	2147	3196	948	2248	1776
100	99957	4872	2710	2161	3302	1049	2253	1660

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 8
0	0	4877	3702	1174	0	0	0	3702
10	10087	4877	2970	1906	2084	105	1978	2864
20	20174	4872	2903	1969	2262	211	2050	2691
30	30262	4877	2859	2017	2412	317	2094	2542
40	39891	4877	2830	2046	2546	418	2127	2412
50	49978	4872	2806	2065	2676	524	2152	2282
60	59607	4872	2792	2079	2802	625	2176	2166
70	70153	4872	2777	2094	2932	736	2195	2041
80	79782	4872	2763	2108	3076	837	2238	1925
90	90328	4872	2749	2123	3196	948	2248	1800
100	99957	4872	2734	2137	3302	1049	2253	1685

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 9
0	0	4872	3721	1150	0	0	0	3721
10	9628	4877	2975	1901	2084	101	1983	2874
20	19716	4877	2898	1978	2257	207	2050	2691
30	30262	4877	2854	2022	2407	317	2089	2537
40	39891	4877	2821	2055	2546	418	2127	2402
50	49978	4872	2787	2084	2686	524	2161	2262
60	60066	4872	2763	2108	2821	630	2190	2132
70	69694	4872	2744	2127	2927	731	2195	2012
80	79782	4872	2724	2147	3052	837	2214	1887
90	90328	4872	2705	2166	3196	948	2248	1757
100	100415	4872	2700	2171	3297	1054	2243	1646

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 10
0	0	4872	3702	1169	0	0	0	3702
10	9628	4872	2980	1892	2070	101	1969	2879
20	20174	4872	2912	1959	2253	211	2041	2700
30	30262	4872	2874	1997	2412	317	2094	2556
40	39891	4877	2840	2036	2546	418	2127	2421
50	50437	4877	2821	2055	2691	529	2161	2291
60	60066	4877	2802	2075	2816	630	2185	2171
70	69694	4872	2782	2089	2927	731	2195	2050
80	79782	4872	2773	2099	3052	837	2214	1935
90	90328	4872	2753	2118	3182	948	2233	1805
100	100415	4872	2739	2132	3331	1054	2277	1685

# Insert LED, press button 1 to start...
# INOM	ILED	VccLED	VD	VLED	VG	VS	VGS	VDS	<--- LED 11
0	0	4877	3707	1169	0	0	0	3707
10	10087	4877	2970	1906	2084	105	1978	2864
20	20174	4877	2907	1969	2257	211	2046	2696
30	30262	4872	2869	2002	2412	317	2094	2551
40	39891	4872	2845	2026	2546	418	2127	2426
50	50437	4872	2821	2050	2686	529	2156	2291
60	60066	4872	2806	2065	2821	630	2190	2176
70	70153	4872	2792	2079	2941	736	2205	2055
80	80240	4872	2777	2094	3061	842	2219	1935
90	90328	4872	2773	2099	3187	948	2238	1824
100	100415	4872	2758	2113	3317	1054	2262	1704

# Insert LED, press button 1 to start...

The Bash / Gnuplot script that produces them:

#!/bin/sh
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
base="${1%.*}"
echo Base name: ${base}
ofile=${base}.png
echo Input file: $1
echo Output file: ${ofile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "${base}"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set xlabel "Forward Voltage - V"
set format x "%6.3f"
set xrange [1.8:2.2]
#set xtics 0,5
set mxtics 2
#set logscale y
#set ytics nomirror autofreq
set ylabel "Current - mA"
set format y "%4.0f"
set yrange [0:120]
set mytics 2
#set y2label "right side variable"
#set y2tics nomirror autofreq 2
#set format y2 "%3.0f"
#set y2range [0:200]
#set y2tics 32
#set rmargin 9
set datafile separator "\t"
set label 1 "LED 1 = LED 11" at 2.100,110 right font "arialbd,18"
set arrow from 2.100,110 to 2.110,103 lt 1 lw 2 lc 0
plot    \
"$1" index 0:9 using (\$5/1000):(\$2/1000):(column(-2)) with linespoints lw 2 lc variable,\
"$1" index 10 using (\$5/1000):(\$2/1000) with linespoints lw 2 lc 0
EOF

And the Arduino source code, which bears a remarkable resemblance to the original firmware:

// LED Curve Tracer
// Ed Nisley - KE4ANU - December 2012

#include <stdio.h>

//----------
// Pin assignments

const byte PIN_READ_LEDSUPPLY = 0;    // AI - LED supply voltage        blue
const byte PIN_READ_VDRAIN = 1;        // AI - drain voltage            red
const byte PIN_READ_VSOURCE = 2;    // AI - source voltage            orange
const byte PIN_READ_VGATE = 3;        // AI - VGS after filtering        violet

const byte PIN_SET_VGATE = 11;        // PWM - gate voltage            brown

const byte PIN_BUTTON1 = 8;            // DI - button to start tests    green
const byte PIN_BUTTON2 = 7;            // DI - button for options        yellow

const byte PIN_HEARTBEAT = 13;        // DO - Arduino LED
const byte PIN_SYNC = 2;            // DO - scope sync output

//----------
// Constants

const int MaxCurrent = 100;                // maximum LED current - mA
const int ISTEP = 10;                    // LED current increment

const float Vcc = 4.930;                // Arduino supply -- must be measured!

const float RSense = 10.500;            // current sense resistor

const float ITolerance = 0.0005;        // current setpoint tolerance

const float VGStep = 0.019;                // increment/decrement VGate = 5 V / 256

const byte PWM_Settle = 5;                // PWM settling time ms

#define TCCRxB 0x01                        // Timer prescaler = 1:1 for 32 kHz PWM

#define MK_UL(fl,sc) ((unsigned long)((fl)*(sc)))
#define MK_U(fl,sc) ((unsigned int)((fl)*(sc)))

//----------
// Globals

float AVRef1V1;                    // 1.1 V bandgap reference - calculated from Vcc

float VccLED;                    // LED high-side supply

float VDrain;                    // MOSFET terminal voltages
float VSource;
float VGate;

unsigned int TestNum = 1;

long unsigned long MillisNow;

//-- Read AI channel
//      averages several readings to improve noise performance
//        returns value in mV assuming VCC ref voltage

#define NUM_T_SAMPLES    10

float ReadAI(byte PinNum) {

word RawAverage;

digitalWrite(PIN_SYNC,HIGH);                // scope sync

RawAverage = analogRead(PinNum);            // prime the averaging pump

for (int i=2; i <= NUM_T_SAMPLES; i++) {
RawAverage += (word)analogRead(PinNum);
}

digitalWrite(PIN_SYNC,LOW);

RawAverage /= NUM_T_SAMPLES;

return Vcc * (float)RawAverage / 1024.0;

}

//-- Set PWM output

void SetPWMVoltage(byte PinNum,float PWMVolt) {

byte PWM;

PWM = (byte)(PWMVolt / Vcc * 255.0);

analogWrite(PinNum,PWM);
delay(PWM_Settle);

}

//-- Set VGS to produce desired LED current
//        bails out if VDS drops below a sensible value

void SetLEDCurrent(float ITarget) {

float ISense;                // measured current
float VGateSet;            // output voltage setpoint
float IError;                // (actual - desired) current

VGate = ReadAI(PIN_READ_VGATE);                    // get gate voltage
VGateSet = VGate;                                    //  because input may not match output

do {

VSource = ReadAI(PIN_READ_VSOURCE);
ISense = VSource / RSense;                        // get LED current

//    printf("\r\nITarget: %lu mA",MK_UL(ITarget,1000.0));
IError = ISense - ITarget;

//    printf("\r\nISense: %d mA VGateSet: %d mV VGate %d IError %d mA",
//           MK_U(ISense,1000.0),
//           MK_U(VGateSet,1000.0),
//           MK_U(VGate,1000.0),
//           MK_U(IError,1000.0));

if (IError < -ITolerance) {
VGateSet += VGStep;
//      Serial.print('+');
}
else if (IError > ITolerance) {
VGateSet -= VGStep;
//      Serial.print('-');
}

VGateSet = constrain(VGateSet,0.0,Vcc);
SetPWMVoltage(PIN_SET_VGATE,VGateSet);

VDrain = ReadAI(PIN_READ_VDRAIN);        // sample these for the main loop
VGate = ReadAI(PIN_READ_VGATE);
VccLED = ReadAI(PIN_READ_LEDSUPPLY);

if ((VDrain - VSource) < 0.020) {            // bail if VDS gets too low
printf("# VDS=%d too low, bailing\r\n",MK_U(VDrain - VSource,1000.0));
break;
}

} while (abs(IError) > ITolerance);

//    Serial.println(" Done");
}

//-- compute actual 1.1 V bandgap reference based on known VCC = AVcc (more or less)
//        adapted from http://code.google.com/p/tinkerit/wiki/SecretVoltmeter

float ReadBandGap(void) {

word ADCBits;
float VBandGap;

ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);    // select 1.1 V input
delay(2); // Wait for Vref to settle

ADCSRA |= _BV(ADSC);                                        // Convert
while (bit_is_set(ADCSRA,ADSC));

ADCBits = ADCL;
ADCBits |= ADCH<<8;

VBandGap = Vcc * (float)ADCBits / 1024.0;
return VBandGap;
}

//-- Print message, wait for a given button press

void WaitButton(int Button,char *pMsg) {
printf("# %s",pMsg);
while(HIGH == digitalRead(Button)) {
delay(100);
digitalWrite(PIN_HEARTBEAT,!digitalRead(PIN_HEARTBEAT));
}

delay(50);                // wait for bounce to settle
digitalWrite(PIN_HEARTBEAT,LOW);
}

//-- Helper routine for printf()

int s_putc(char c, FILE *t) {
Serial.write(c);
}

//------------------
// Set things up

void setup() {
pinMode(PIN_HEARTBEAT,OUTPUT);
digitalWrite(PIN_HEARTBEAT,LOW);    // show we arrived

pinMode(PIN_SYNC,OUTPUT);
digitalWrite(PIN_SYNC,LOW);        // show we arrived

TCCR1B = TCCRxB;                    // set frequency for PWM 9 & 10
TCCR2B = TCCRxB;                    // set frequency for PWM 3 & 11

pinMode(PIN_SET_VGATE,OUTPUT);
analogWrite(PIN_SET_VGATE,0);        // force gate voltage = 0

pinMode(PIN_BUTTON1,INPUT_PULLUP);    // use internal pullup for buttons
pinMode(PIN_BUTTON2,INPUT_PULLUP);

Serial.begin(9600);
fdevopen(&s_putc,0);                // set up serial output for printf()

printf("# LED Curve Tracer\r\n# Ed Nisley - KE4ZNU - December 2012\r\n");

VccLED = ReadAI(PIN_READ_LEDSUPPLY);
printf("# VCC at LED: %d mV\r\n",MK_U(VccLED,1000.0));

AVRef1V1 = ReadBandGap();            // compute actual bandgap reference voltage
printf("# Bandgap reference voltage: %lu mV\r\n",MK_UL(AVRef1V1,1000.0));

}

//------------------
// Run the test loop

void loop() {

Serial.println('\n');                        // blank line for Gnuplot indexing

WaitButton(PIN_BUTTON1,"Insert LED, press button 1 to start...\r\n");
printf("# INOM\tILED\tVccLED\tVD\tVLED\tVG\tVS\tVGS\tVDS\t<--- LED %d\r\n",TestNum++);
digitalWrite(PIN_HEARTBEAT,LOW);

for (int ILED=0; ILED <= MaxCurrent; ILED+=ISTEP) {
SetLEDCurrent(((float)ILED)/1000.0);
printf("%d\t%lu\t%d\t%d\t%d\t%d\t%d\t%d\t%d\r\n",
ILED,
MK_UL(VSource / RSense,1.0e6),
MK_U(VccLED,1000.0),
MK_U(VDrain,1000.0),
MK_U(VccLED - VDrain,1000.0),
MK_U(VGate,1000.0),
MK_U(VSource,1000.0),
MK_U(VGate - VSource,1000),
MK_U(VDrain - VSource,1000.0)
);
}

SetPWMVoltage(PIN_SET_VGATE,0.0);

}

,

4 Comments

Merry Christmas: Winter Visitors

Our back yard serves as a wildlife thoroughfare, but only after a snowfall can we see who’s been afoot overnight.

Gray squirrels hop across the driveway:

Squirrel Tracks in Snow

Squirrel Tracks in Snow

When they’re not busy raiding the bird feeder, that is:

Not a Squirrel-Proof Feeder

Not a Squirrel-Proof Feeder

Red foxes leave widely spaced tracks:

Red Fox Tracks in Snow

Red Fox Tracks in Snow

Even quadrupeds have trouble maintaining their footing on an icy driveway:

Red Fox Skidmark in Snow

Red Fox Skidmark in Snow

Turkeys travel in flocks:

Turkey Tracks in Snow

Turkey Tracks in Snow

And sometimes monsters stride the Earth:

Mary Track in Snow

Mary Track in Snow

Seeing as how it wouldn’t be a suitable blog post without some numbers, here’s a 1 foot / 30 cm scale with fox and turkey tracks:

Turkey and Fox Tracks in Snow with Ruler

Turkey and Fox Tracks in Snow with Ruler

Those are scary-big birds!

Merry Christmas to all!

8 Comments