Posts Tagged Memo to Self
Spotted while in the midst of replacing my Tour Easy’s rear grip shifter:
As you might expect, the cable saws through the side of its ferrule and the brazed-on frame fitting, because it’s been basically impossible (for me, anyhow) to find a replacement derailleur duplicating whatever the good folks at Easy Racers shipped back in 2001.
On the upside, this derailleur’s cable entry has a nicely rounded ramp eliminating the need for my brass cable pulley widget.
Memo to Self: Perhaps running the cable around a bearing anchored to the frame fitting would help?
I’ve obviously forgotten to fix this for several years, so putting it here may serve as a Round Tuit.
Speaking of automotive fuses, our 2015 Subaru Forester has a pair of fuse boxes, hereby documented in case of need.
One under the hood:
Note the white fuse puller near the top.
The layout chart doesn’t say what “SBF” might be, but we have a lot of whatever it is:
The spare fuses line up along the lower edge of the cover.
Another under the dashboard:
And their functions:
The string of fuses down the right side of the main block looks like a line of spares, but they’re not. What they might be isn’t documented anywhere, which seems to be very deliberate.
Memo to Self: Having never replaced an automotive fuse, I shouldn’t start worrying now.
Some ex post facto notes from the second SquidWrench Electronics Workshop. This turned out much more intense than the first session, with plenty of hands-on measurement and extemporized explanations.
Measure voltage across and current through 4.7 kΩ 5 W resistor from 0.5 V to 30 V. Note importance of writing down what you intend to measure, voltage values, units. Plot data, find slope, calculate 1/slope.
Introduce parallel resistors: 1/R = 1/R1 + 1/R2. Derive by adding branch currents, compute overall resistance, factor & reciprocal.
Review metric prefixes and units!
Introduce power equation (P = E I) and variations (P = I² R, P = E²/R)
Measure voltage across and current through incandescent bulb (6 V flashlight) at 0.1 through 6 V, note difference between voltage at power supply and voltage across bulb. Plot data, find slopes at 1 V and 5 V, calculate 1/slopes.
Measure voltage across ammeter with bulb at 6 V, compute meter internal resistance, measure meter resistance. Note on ammeter resistance trimming.
Measure voltage across and current through hulking power diode from 50 mV – 850 mV. Note large difference between power supply voltage and diode voltage above 750-ish mV. Note power supply current limit at 3 A. Plot, find slopes at 100 mV and 800 mV, calculate 1/slopes. Compare diode resistance with ammeter resistance.
Review prefixes and units!
The final whiteboard:
Hand-measured data & crude plots FTW!
Some ex post facto notes from the first SquidWrench Electronics Workshop, in the expectation we’ll run the series from the start in a while. I should have taken pictures of my scribbles on the whiteboard.
- Voltage – symbol E (Electromotive Force or some French phrase), unit V = volt
- Current – symbol I (French “intensity” or some such), unit A = ampere
- Resistance – symbol R (“resistance”), unit Ω (capital Greek Omega) = ohm
Introduce Ohm’s Law & permutations, postpone calculations.
Measure the actual voltage of assorted cells & batteries. Identify chemistry, internal wiring:
- 1.2 = nickel-cadmium or nickel-metal-hydride
- 1.5 = carbon-zinc or alkaline
- 2 V = lead-acid
- 3.0 = primary lithium
- 3.6 – 3.7 = rechargeable lithium, several variations
- 4.8 = 4 x 1.2 V
- 7.2 = 6 x 1.2 V
- 7.4 = 2 x 3.6 V
- 9.6 = 8 x 1.2 V
- 10.8 = 3 x 3.6 V
- 12 = 6 x 2 V
Measure various resistors, favoring hulking finger-friendly sandstone blocks.
Introduce metric prefixes:
- Engineering notation uses only multiple-of-three exponents
- μ = micro = 10-6
- m = milli = 10-3
- k = kilo = 103
- M = mega = 106
Discuss resistor power dissipation vs. size vs. location, postpone power formula.
Clip-lead various resistors to various batteries, measure voltage & current.
Now compute permutations of Ohm’s Law using actual data!
This 2 GB flash drive arrived with datasheets & sample files for a (computerized) sewing machine Mary eventually decided she wasn’t going to get (because computerized):
Being of sound mind, we reformatted it and dropped it in the bag o’ random drives. She eventually used it for one of her gardening presentations, whereupon the library’s (Windows) laptop said it needed formatting; she pulled out a backup drive and continued the mission.
Lather, rinse, verify a good format, verify presentation files on the Token Windows Box, and repeat, right down to having another library’s laptop kvetch about the drive.
Soooo, I did what I should have done in the first place:
sudo f3probe -t /dev/sdc F3 probe 6.0 Copyright (C) 2010 Digirati Internet LTDA. This is free software; see the source for copying conditions. WARNING: Probing normally takes from a few seconds to 15 minutes, but it can take longer. Please be patient. Probe finished, recovering blocks... Done Bad news: The device `/dev/sdc' is a counterfeit of type limbo You can "fix" this device using the following command: f3fix --last-sec=25154 /dev/sdc Device geometry: *Usable* size: 12.28 MB (25155 blocks) Announced size: 1.86 GB (3893248 blocks) Module: 2.00 GB (2^31 Bytes) Approximate cache size: 511.00 MB (1046528 blocks), need-reset=no Physical block size: 512.00 Byte (2^9 Bytes) Probe time: 55'18" Operation: total time / count = avg time Read: 8'35" / 3145715 = 163us Write: 46'37" / 18838872 = 148us Reset: 350.7ms / 2 = 175.3ms
As long as you don’t write more than a few megabytes, it’s all good, which was apparently enough for its original use.
The front of the PCB looks normal:
But it seems they really didn’t want you to see the flash chip:
Given the two rows of unused pads, it must be a really small chip!
Memo to Self: Always examine the dentition of any Equus ferus received as a gift.
Separately charging all four cells from the Baofeng BL-5 packs covered the Electronics Bench with wires:
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:
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:
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:
Unfortunately, two APRS iGates vanished in the last year, leaving poor coverage south of Poughkeepsie.
A Pogo Pin reference may be useful:
- P.. and R.. refer to Pin and Receptacle (a.k.a. socket), respectively
- Pxx and Rxx = nominal pin diameter in 0.01 mm units: P50 = 0.48 mm
For pins, the suffix -hn indicates pin head shape, the most useful of which may be:
- B1: 45° cone
- J1: dome end
- Dx: large dome, also 1D
- Gx: cylinder
- Ex: large 90° cone, sometimes 1E
- T2 – large chisel
For sockets, the suffix -ntl gives:
- n – entry shape: 1 = shaped entry, 2 = straight entry
- t – termination: C = crimp, S = solder, W = wire
- l – length of wire in 100 mm units: 7 = 700 mm
From what I can find on eBay, all pins have 6 mm travel with typically 75 / 100 / 180 g spring force.
A picture ripped from the reference to forestall link rot:
Memo to Self: US-based eBay sellers charge three times more than Chinese sellers, but deliver in one-third the time.
[Update: Simon sends a link to Everett Charles Technologies, a pogo-pin manufacturer providing “Probably much more information than anyone should ever want”. Of course, eBay / Amazon junk may not meet any particular specs, so scale your expectations accordingly.]