Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
So the outdoor thermometer hanging over my desk became very, very faint, which suggested it was time for a new alkaline cell. The last time that happened, the insides were pretty bad, so I expected the worst, but, surprisingly, neither the cell nor the negative contact spring were corroded. So I popped in a new cell, buttoned it up, and … it didn’t work. At all. As in: blank display.
Taking the back off revealed the simple cause:
Outdoor thermometer – corroded battery lead
Evidently, the negative terminal wire had corroded completely through and popped off when I replaced the cell. There’s plenty of green-blue corrosion on the terminal inside the case, where it can’t be seen from outside; three years ago I cleaned up both the outside and inside, so this is new news.
The negative wire was discolored all the way from end to end and couldn’t be soldered. I think the corrosion products are just slightly hygroscopic and wick their way along the copper strands inside the insulation: the solder pad on the circuit board was also discolored.
I removed the terminal, neutralized the alkaline corrosion, ran it through an Evapo-Rust bath, scrubbed it clean, installed it, replaced both the positive and negative wires, resoldered everything, and it works perfectly again.
The dotted curve comes from Figure 29-22 of the ATmega168 datatsheet and shows the typical source current vs. voltage for a digital output pin on your favorite Arduino.
The cheerful colored curves show the current vs. voltage characteristics of some random LEDs, with data from the same curve tracer setup as those.
Given a particular LED directly connected between an Arduino output pin and circuit common (without the formality of a current-limiting ballast resistor), the intersection of the dotted output pin curve with the colored LED curve gives you the current & voltage at the pin. For example, the violet LED would operate at 4 V and 40 mA.
Some gotchas:
Typical 5 mm LEDs, of the sort one might use for this experiment, have a maximum DC current limit of 20 mA
Arduino output pins have an absolute maximum current limit of 40 mA
So all of the direct solutions drive too much current through the LED. Although the blue and violet LEDs don’t quite exceed the output pin limit, the others certainly do. Those old standby red & amber LEDs would have absurdly high intercepts, well beyond the limit of sanity, in the region where the data you see here breaks down, where the pin driver gives up and goes poof, not that that ever stopped anybody from trying.
You’ve probably seen somebody do it. Next time, aim ’em here in a non-confrontational manner… [grin]
My Arduino Survival Guide presentation has other info that may help that poor sweating Arduino survive. You don’t get my performance-art patter, but the pictures and captions should carry the tale…
As part of conjuring up this plot, I discovered that, for whatever reason, Gnuplot’s TrueType font rendering (via gdlib) no longer works in Xubuntu 12.04: the font name has no effect whatsoever, but the point size does.
The Gnuplot source code:
#!/bin/sh
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/msttcorefonts"
Pinfile="ATmega Pin Driver Data - Source.csv"
LEDfile="LED Data.csv"
base="Arduino Pin Driver - Direct LED Load"
Outfile="${base}.png"
echo Output file: ${Outfile}
fontname="Arial"
echo Font: ${fontname}
#-- do it
gnuplot << EOF
#set term x11
set term png font "${fontname},18" size 950,600
set output "${Outfile}"
set title "${base}" font "${fontname},22"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set xlabel "Pin Voltage - V"
set format x "%4.1f"
set xrange [0:${vds_max}]
#set xtics 0,5
set mxtics 2
#set ytics nomirror autofreq
set ylabel "Pin Current - mA"
#set format y "%4.1f"
set yrange [0:80]
#set mytics 2
#set y2label "Drain Resistance - RDS - mohm"
#set y2tics nomirror autofreq ${rds_tics}
#set format y2 "%3.0f"
#set y2range [0:${rds_max}]
#set y2tics 32
#set rmargin 9
set datafile separator "\t"
set label "Pin IOH" at 3.0,70 center font "${fontname},18"
set label "Pin Abs Max" at 1.4,40 right font "${fontname},18"
set arrow from 1.5,40 to 4.75,40 lw 4 nohead
set label "LED Max" at 1.4,20 right font "${fontname},18"
set arrow from 1.5,20 to 4.75,20 lw 4 nohead
plot \
"${Pinfile}" using 1:3 with lines lt 0 lw 3 lc -1 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 0:0 with lines lw 3 lc 1 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 1:1 with lines lw 3 lc 2 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 2:2 with lines lw 3 lc 0 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 3:3 with lines lw 3 lc 4 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 4:4 with lines lw 3 lc 3 ,\
"${LEDfile}" using (\$5/1000):((\$1>0)?\$2/1000:NaN) index 5:5 with lines lw 3 lc 7
EOF
A few early risers got to see a completely broken listing, with all the quotes and brackets and suchlike reduced to the usual HTML escaped gibberish…
After that rebuild, the first five recharges went like this: 21, 21, 21, 23, and 20 days. The last interval included seven days of vacation, during which the battery suffered just the usual self-discharge common to NiMH cells.
That’s about what the OEM battery delivered, back when it was new, so the new 600 mA·h cells seem to be about the right capacity. Obviously, the end of the OEM battery wasn’t nearly so pretty.
In round numbers, the wireless charger requires one hour to restore the energy drawn by one two-minute brushing: the thing charges for about 21 hours. There’s additional loss from three weeks of self-discharge in there: if 7 days of non-use = 1 brushing, then the usual 21 days = 3 brushings -> 14% loss due to self-discharge.
I’d take a large grain of salt with those numbers…
The plunger is basically a pin that eventually deforms the top of the switch membrane. Tee’s DSC-H1 had an exposed switch, although this picture shows that membrane was still in reasonably good condition:
Shutter Switch Closeup
My DSC-H5 has a thin black protective disk atop the switch, but the disk wasn’t particularly protective and developed a dimple that held the contacts closed even with the shutter button released (which is why I’m tearing the camera apart in the first place):
DSC-H5 Shutter Switch – dimpled protector
The C-clip around the plunger is now plastic, rather than metal, making it less likely to erode the thin plastic shaft. Pulling the clip off while holding the button down releases all the parts:
DSC-H5 Shutter Button – components
A few measurements from an intact shutter button, which may come in handy if you don’t have one:
DSC-H5 Shutter Button – plunger measurements
Mount three-jaw chuck on the Sherline table, laser-align chuck to spindle, grab shutter button by its shaft in a Jacobs chuck, grab shutter button in three-jaw chuck, release from Jacobs chuck:
DSC-H5 Shutter Button – in Sherline chuck
That’s not particularly precise, but it’s close enough for this purpose. I used manual jogging while testing the fit with a paper shim until all three jaws had the same clearance, then tightened the jaws.
I nicked the plunger at its base with a flush-cutting diagonal cutter, snapped off the plunger, and drilled a #56 hole through the button:
DSC-H5 Shutter Button – cap drilling
For reasons that made sense at the time, I repaired Tee’s DSC-H1 with a 1-72 brass screw. This time, I used an 0-80 (which I learned as ought-eighty, if you’re wondering about the indefinite article) screw and nut, because the screw head fit neatly into the bezel recess and I had a better idea of how to smooth out the threads.
This being plastic, I used the chuck to hold the tap in the proper alignment, then turned the tap through by finger pressure. This trial fit showed it worked:
DSC-H5 Shutter Button – 0-80 screw
Milling the nut down to a 2.8 mm cylinder required the usual manual CNC, with repeated iterations of this chunk of code in the MDI panel:
The 2.8 in the first line is the current OD and the 3.11 is the measured diameter of the 1/8 inch end mill. I started from a 5.0 mm OD that just kissed the nut, then worked inward by 0.2 mm at a time for very shallow 0.1 mm cuts:
DSC-H5 Shutter Button – 0-80 nut milling
The alert reader will notice, as did I, that the head isn’t quite centered: the cut trimmed the left side and left the right untouched, with an offset far larger than the centering error. As nearly as I can tell, the heads of those screws aren’t exactly centered on their threaded shafts, but the final result fixed that… and the overall error is a few tenths of a millimeter = maybe 10 mils, tops, so it’s no big deal.
With all that in hand, I applied a very very thin layer of epoxy to fill the threads below the now-cylindrical nut and convert the screw into a rod:
DSC-H5 Shutter Button – 0-80 plunger
My original intent was to use the screw head as-is atop the PET shield (per those instructions) on the switch membrane, but after reassembling enough of the camera to try that out, it didn’t work correctly: the half-pressed switch didn’t activate reliably before the full-pressed switch tripped.
The PET shield I used came from the side of a 1 liter soda bottle and turned out to be 0.27 mm thick:
DSC-H5 Shutter Switch – cover removed
I think the PET shield would work with the original plunger shape concentrating the force in the middle of the shield, but the nice flat screw head spreads the force out over a wider area. As a result, the force required to close the half-pressed switch contacts was roughly the same as that required to close the full-pressed contacts; remember the nub on the bottom of the black plastic tray concentrates the force in the middle of the full-pressed switch membrane.
So I removed the PET shield, added a dot of epoxy to fill the screw slot and compensate for the missing shield thickness, then filed a flat to make a nice pad:
DSC-H5 Shutter Button – epoxy on plunger
Reassembling the camera once more showed it worked exactly the way it should. In fact, the button seems more stable than the OEM version, probably because the slightly enlarged plunger shaft fits better in the bezel. Too bad about those scuffs on that nice shiny button dome, though:
DSC-H5 – repaired shutter button
Tossing the leftover parts seems entirely appropriate…
The bikes stand upright inside the van and the helmets ride on the floor with all their stalks sticking up. This usually works out well, but on our last trip my helmet rolled under my bike and rubbed the foam ball surrounding its mic against the chain, producing a result so awful that I had to install new foam.
The foam comes from a sheet of Sonex acoustic foam baffle, snipped into a reasonable approximation of a ball, with a slit deep enough to surround the mic, and a cable tie holding it closed:
Foam mic ball on bike helmet boom
For what it’s worth, I’ve found that excessive wind noise correlates with too much mic gain. The mic rides about a finger’s width from the corner of my mouth, I talk at a normal volume, the amp supplies about 20 dB of gain, and we have no trouble with wind noise. The amp gain depends on the mic sensitivity, so your results will certainly differ; these mics came from the heap with no specs whatsoever.
I suppose wind noise also depends on the bike’s speed, but when I’m going that fast I don’t have enough brain or lungs left over to hold a conversation…
Our Toyota Sienna arrived with a blank cover plate where a fancier model would have a switch. It seemed a shame to let that space go to waste, so I popped the plate out, rummaged around in the heap, found a small circuit board with a blinky LED that just exactly fit the space available, and drilled a suitable hole:
Sienna anti-theft blinker – inside
When it’s installed in the van, it looks and acts just like the security system we don’t have. For all I know, that plate was for the security system control, so perhaps it’s an exact match!
Sienna anti-theft blinker – bezel
The batteries last about two years, a few months later I notice the lack of blinkiness (it’s hidden behind the steering wheel in my normal driving position), and eventually I replace the corroded batteries. This time, I had to replace the entire battery holder; things got pretty nasty in there.
As I recall, the PCB came from a fancy “greeting card” mailed to me by the Business Software Alliance, with the implied threat that if all my paperwork wasn’t up to par, my use of potentially unlicensed software would blow up in my face. That was back in the day when mailing something that pretended to be a bomb was considered a cute joke and when I actually ran more than one Windows PC.
It seems that Wouxun KG-UV3D HTs require nearly 0 V to activate the PTT input, which I discovered after the radio on Mary’s bike began acting intermittently. The TinyTrak3+ would transmit correctly, but the PTT button on the handlebar began to not work at all / work intermittently / work perfectly. The switch and cable were OK, pushing the button produced nearly 0 Ω at the 3.5 mm plug, the connections seemed solid, but the radio didn’t transmit reliably.
I finally got the thing to fail on the bench, which led to the discovery that:
Shorting the PTT input to the GPS+voice adapter PCB to ground didn’t make the radio transmit and
Data bursts from the TinyTrack3 worked perfectly
Gotcha!
TT3 PTT In-Out
The TT3+ pulls its PTT OUT pin down from +5 V using a 2N2222A NPN transistor (off to the right in the schematic snippet), but, for reasons having to do with ESD, the input from the PTT switch on the handlebars goes through a 100 Ω series resistor, then passes to the TT3 board through PTT IN to D6 before joining the TT3 transistor collector. The low-active diode-ORed signal heads off through PTT OUT to a 10 Ω series resistor, thence to the KG-UV3D PTT input. D6 is an ordinary 1N4148, with the net result that the PTT input voltage at the radio dropped to 630 mV with the PTT button pressed.
Not finding anything else wrong, I replaced D6 with a BAT54 Schottky diode that pulled the PTT voltage down to 300 mV and the radio worked fine.
Of course, a BAT54 is a surface-mount diode, so I clipped off the unused no-connect lead (it’s the only way to be sure it doesn’t do anything) and tacked it down slaunchwise between the PCB thru-hole pads. If I had a BAT54C with common cathodes, I could replace both D5 and D6 in one shot, but D5 just pulls down a PIC input that has an ordinary logic-level threshold voltage.
I don’t know why the KG-UV3D PTT is so fussy, although it may really be a current-driven signal that requires more current than can flow through the 110 Ω + diode forward drop in series with the PTT button. Wouxun presents no specifications that I can find.
The identical circuitry on my bike works fine with the stock D6 diode and a presumably identical KG-UV3D. I should replace that diode before it gives me any trouble, but I’ll wait until I must take the box apart for some other reason.
The Smell of Molten Projects in the Morning 