Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The probes report a resistance of 270 mΩ (net of the 50 mΩ probe-to-probe resistance), as close as one could ask to the nominal 26 Ω/1000 ft spec for 24 AWG wire at the current Basement Laboratory temperature.
They are exceedingly limp and flexy, due to many teensy conductors; not at all like PVC hookup wire.
If you’re willing to buy 500 feet of each color, the cost-per-foot from a reputable supplier gets downright competitive, but I’m not in that market.
A QRPme Pocket Pal II could be a suitable project for a Squidwrench “advanced soldering” class:
QRPme Pocket Pal II – front
Yes, it comes with a tin case:
QRPme Pocket Pal II – tin case
You must fit your own insulating sheet under the PCB; polypropylene snipped from a retail package works fine.
It’s intended as a “mint tin sized tester for all kinds of hamfest goodies”, but it seems like a nice source of small currents, voltages, and signals suitable for stimulating all manner of circuitry one might encounter in later sessions of a beginningelectronics class.
Before using it, of course, one must solder a handful of small through-hole parts into the PCB, a skill none of us were born with.
For completeness, the back side, hot from the soldering iron:
QRPme Pocket Pal II – rear
The kits (always buy two of anything like this) arrived minus a few parts, which I suspect was due to an avalanche of orders brought on by a favorable QST review. Fortunately, I (still) have a sufficient Heap o’ Parts to finish it off without resupply, although a hank of 9 V battery snaps will arrive in short order.
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 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.
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.
Define:
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
The genuine Sony NP-BX1 that came with the AS30V camera suffers from voltage depression (green trace) and no longer survives a typical ride:
Sony NP-BX1 – 2018-04-24
The STK C battery (red trace) is also pretty much kaput, so the two of them go into the recycle bag.
The very short blue trace is the Wasabi F battery after a ride, showing about 1 W·h remaining of the initial charge. After a full change, the upper blue trace shows it has a capacity in the same range as the others. Our rides are about an hour long, so the camera draws somewhat less than the 1 A test current, roughly what I’d estimated from other data.
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The overall XY travel is slightly smaller than the initial configuration, because the router sticks out further than the penholder I’d been using. Increasing the $27 Homing Pulloff distance to 3 mm leaves a comfortable space beyond the limit switches after homing to the positive end:
MPCNC – X-axis endstop – home
Adjusting the $13[01] XY travel distances and switch positions on the other end of the rail leaves a similar comfort zone at the negative end:
MPCNC – X-axis endstop – X min
Both switches now live on the rear X-axis rail and appear as seen from behind the bench; they just look backwards. The Y-axis switches are on the left rail and look exactly the same.
The XY travel works out to 630 × 460 mm = 24.8 × 18.1 inch, which is Good Enough.
Some fiddling with the Z axis limit switch tape mask produces a nice round 100 mm = 3.9 inch vertical travel. The Z-axis rails just barely clear the table at the lower limit and just barely stay in the bottom bearings at the upper limit, so it’s a near thing. In practical terms, the rails or the tool will smash into the workpiece sitting atop the table before the limit switch trips.
Setting both $20=1 Soft Limits and $21=1 Hard Limits may be excessive, but I vastly prefer having the firmware detect out-of-range moves and the hardware forcibly shut down if the firmware loses track of its position, rather than letting it grind away until I can slap the BRS. The steppers aren’t powerful enough to damage anything, of course, so it’s a matter of principle.
The $N1=G10L2P1X-633Y-463Z-3 sets the default G54 coordinate origin to the front-left corner, with Z=0 at the home position up top, so as to prevent surprises. I expect to use G55 for most work holder touchoffs, although we’ll see how that plays out.
The G28 and G30 settings depend on the tool change location and the Z-axis probe location, so they’re still not cast in concrete.
The Smell of Molten Projects in the Morning 