Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The 18650 cell protection PCBs with 8205 ICs arrived and seemed small enough to simply tuck into the gap between the rounded cells in the second Baofeng BL-5 pack:
Baofeng BL-5 – new protection PCB – wiring 1
For whatever it might be worth, you’re looking at the only Baofeng battery pack containing an actual 10 kΩ thermistor, harvested from the benchtop Tray of Doom:
Baofeng BL-5 pack – thermistor
Unfortunately, the components on the PCB stuck up a bit too far from the cell surface and held the lid just slightly proud of the case. Applying pressure to lithium cells being a Bad Idea, I rearranged the layout by flipping the cells over, tucking the PCB components between the cells, and connecting everything with nickel tape instead of insulated wires:
Baofeng BL-5 – new protection PCB – wiring 2
The snippets of manila paper and Kapton tape hold things apart and together, as needed. Looks ugly, fits better.
Pop it in the charger to reset the protection PCB lockout and it’s all good again.
My original idea for the APRS + voice gadget was a snap-in battery pack replacement holding the circuit boards and connected to an external battery pack. A trio of deadWouxun radios, plus the ready availability of 18650 lithium cells, suggested putting two cells in the backpack, along with the circuitry, and skipping the external pack.
The grid is parallel to the case body and centered left-to-right, with a Y grid line set at the front face of the pack, where it’s also flush with the lid surface. You can read off the coordinates of all the points, feed them into your CAD model, and maybe, with a bit of care, get something 3D-print-able.
Haven’t used it yet, but it’s bound to come in handy at some point.
Although I cannot explain why those ferrite beads lit up, it seems connecting the DE-9 shell to the serial device ground is an Extremely Bad Idea. I removed that wire from the HP 8591 spectrum analyzer cable and everything seems to work, so I’ll declare victory:
Sena PS410 Serial Server – in action
Not shown: the tangle of cables tucked behind that tidy box. You can plug a serial terminal into the DE-9 connector, but it’s much easier to use the PS410’s web interface.
It needs a static IP address to make it findable, although I also told the router to force the same address should it start up in DHCP mode:
IP Configuration
Yeah, Google DNS, if all else fails.
The serial port overview:
Serial port overview
I’ll go into more detail in a while about individual device setups and the scripts slurping screen shots out of them, but giving each one a useful name is a Good Idea, even though it doesn’t appear anywhere else. I changed the default Inactivity Timeout for each port from the default 100 seconds to zero, thereby preventing the PS410 from closing the connection due to inactivity:
Serial Port 2 – host params
The DTR and DSR defaults work out well; the other choices solve problems I don’t have. Indeed, the PS410 has a myriad configuration options best left in their Disabled state.
The serial parameters for each port need tweaking to suit the hardware gadget on the other end of the cable:
Serial Port 2 – serial params
Flow Control applies between the PS410 and the gadget. You can choose:
Disabled
XON/XOFF – in-band characters
RTS/CTS – RS-232 hardware signals
Somewhat to my surprise, It Just Worked despite my blundering.
The USB serial adapters I use to capture HP54602 scope and HP8591 spectrum analyzer screenshots, as well as monitor the HP Z8501 GPS time standard, lack unique identifiers and appear as unpredictable device nodes.
After putting up with this for far too long, I dropped $15 on a Sena Technologies PS410 serial server:
Sena PS410 Serial Server – interior
It needed a new lithium coin cell, of course:
Sena PS410 Serial Server – as-received CR2032
The PCB and chip date codes suggest a 2009 build, so “98” might mean August 2009. Whether that’s the manufacturing date or the best used by date, ya never know.
The eBay deal didn’t include the power supply, so I hacked a coaxial jack on the back:
Sena PS410 Serial Server – hacked power jack
A 14 VDC IBM laptop brick from the pile suits the “9 to 36 V” range printed on the case.
Poking the “factory reset” switch did what you’d expect and the “console” serial port on the front worked fine. I plugged in the scope, the spectrum analyzer, and the GPS receiver, whereupon the bench took on the unmistakable aroma of electronic death:
Sena PS410 Serial Server – charred ferrite chip
Some probing suggests FB9 used to be a ferrite bead between serial port 2’s ground pin and the frame ground.
To compress an afternoon of tinkering into one sentence, there seems to be an occasional 35 VAC difference between the spectrum analyzer and the scope, but only when one or the other is plugged into the PS410. Everything is (now!) plugged into the same branch circuit and, in fact, the same outlet via many power strips, but the difference remains. A different power supply makes no difference, either.
I managed to burn out the ferrite bead on Port 1 with only the scope and the power supply plugged in, by connecting the scope’s ground lead to the shell of Port 2. That makes no sense: there is no voltage difference between the scope’s serial ground and its probe ground.
Something Is Not Right, but I’m baffled.
I have established that the server works fine, even with the charred beads, which is a Good Thing.
A simpleminded MOSFET circuit provides PWM drive for the BLDC blower:
BLDC Fan PWM Test Fixture – schematic
The Tek P6302 current probe looms much larger in real life than in the schematic:
BLDC fan PWM Test Fixture
A quick dataset shows the RPM variation against PWM duty cycle:
BLDC Blower – RPM vs PWM – doodles
Unsurprisingly, the RPM curve resembles the earlier results against a variable DC supply voltage:
BLDC Blower – RPM I P vs V
Capturing the current waveform is stalled behind another project, but it has exactly the voltage spikes you’d expect from forcibly switching an inductive load.
Separately charging all four cells from the Baofeng BL-5 packs covered the Electronics Bench with wires:
Baofeng BL-5 cell charging
The cell sits on a ceramic tile as a nod to fire safety, although I doubt it makes any difference.
The discharge tests showed two nearly identical pairs:
Baofeng BL-5 Cells – Separate Charge – 2018-02-24
Surprisingly, cells A and B (upper traces) were deaders in the original packs. Cells C and D (lower traces) were more-or-less fully charged, but now have a lower terminal voltage and slightly lower capacity. I have no explanation for that, nor for the voltage undulations.
The rebuilt packs pair up A+B and C+D.
Reassembling pairs into the pack shell and resoldering all the leads produces a good pack:
Baofeng BL-5 battery rebuild
I later added a snippet of heavy manila paper under the nickel tape bent around the edge of the pack as a third level of insulation, in the interest of having the nickel tape not produce a dead short between the isolated – terminal and the + cell case.
Memo to Self: tape the long wiggly leads from the protection PCB to the radio contacts (at the left side) before soldering the PCB to the cell terminals, because an inadvertent short will convert the 8205A battery protection IC into a Light-Emitting IC, at least for a moment, and subsequently release the Acrid Smell of Electrical Death. A handful of charge PCBs are en route halfway around the planet, from which I intend to liberate one IC for this board; with luck, I didn’t incinerate anything else.
The pack works fine in the radio, as does the APRS interface:
APRS Coverage in Poughkeepsie – 2018-03-01
Unfortunately, two APRS iGates vanished in the last year, leaving poor coverage south of Poughkeepsie.
Including a waterproof case, some right-angle connectors, and a pipe clamp:
M20 in waterproof case – Tour Easy seat
The stack turns out to be about as flexy as one might imagine, definitely a Bad Thing for a bike-mounted camera, and a somewhat more rugged mount seems in order.
A diagram from the M20 manual shows the parts:
SJCAM M20 Overview – Manual pg 5
Some camera dimensions:
40.2 mm wide + 0.5 mm for the Up/Down buttons
21.8 mm thick + 1.0 mm cylindrical front curve + 1.0 mm rear screen
50.0 mm tall + 4.0 mm cylindrical top curve + buttons
21.7 mm OD × 6.0 mm long lens housing, 1.3 mm down from top center
All the edges have neat chamfers or radius rounding on the order of a few millimeters.
Applying the chord equation to the spans inside the rounding:
Front radius: 162.5 mm
Top radius: 42.5 mm
The new batteries survive for a bit over an hour, not quite enough for our usual rides. Rather than conjure a fake battery pack connected to an external 18650 cell with a wire chewed through the case, the least awful way to go may involve a relatively small battery pack (with internal 18650 cells, of course) plugged into the USB port with a right-angle cable and a rigid mount holding both the camera and the pack to the seat frame.
