Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
mansaxel:
--- Quote from: bd139 on June 25, 2022, 04:39:22 pm ---
--- Quote from: med6753 on June 25, 2022, 04:32:24 pm ---
--- Quote from: TERRA Operative on June 25, 2022, 04:30:28 pm ---
And I'm in as co-author of the sequel "How to Live With a Japanese Wife and Survive" :-DD
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I thought Japanese wimens were submissive and meek? No?
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LOL the one I’m friends with is a deeply cynical vicious sick and twisted individual. Conversion diverged into anal polyps and how good laughing gas is last time. Just how I like them :-DD
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That is marriage material, should one be on that tack in life.
mnementh:
--- Quote from: bd139 on June 25, 2022, 04:23:43 pm ---...As for the book, been mulling the idea of writing a book for about ten years. Subject matter is basically all those bits of info that everyone should know before doing a Udemy “how to code” tutorial. I encounter a lot of people who can’t even visualise what a computer or network looks like past some opaque magic and expect me to fill the gaps in :-DD
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Sounds like a Layer 8 problem to me. :-DD
mnem
Maybe Layer 9... are there any Ronin PHBs floating around...? You'll need a exorcist... >:D
factory:
No luck for me on ePay lately....
Well I got outbid on the hp 5090B receiver. :(
I didn't mention it the other day, but the 5090 was supposedly the first hp TE designed in the UK, they seem quite uncommon too, though maybe a bunch of modified ones will appear on the bay, as spares/repair once the LW radio signal finally becomes EOL. :-BROKE
Also tried to bid on a hp 185B oscilloscope that would have ended Friday at 11.30am, no bids all week, so I though no one else was interested (like the one in Germany that went for a single digit € a while ago). I was working when it ended and snuck away from the BDNL* to bid a ten minutes prior to the end, only to find the ePay mobile programme wouldn't accept my bid |O turns out it sold on an offer about an hour or two before the end. This might or might not have been a good thing, as it was advertised as a "barn find" with minimal pictures and the sellers other "barn finds" looked in quite poor condition. :phew:
*big dirty noisy lathe
David
nfmax:
--- Quote from: capt bullshot on June 25, 2022, 08:48:21 am ---
--- Quote from: nfmax on June 25, 2022, 08:09:26 am ---
A special bonus point to the first person to correctly describe what purpose D1 serves
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I can figure two purposes:
1. help with measuring the quiescent current of parts of the circuit, since you've attached a test point
2. when U1 pin 9 switches, the common R1, R2, C2 node sees voltages below BATT- and above BATT+, the diode will allow the supply voltage of U1 to rise above BATT+ and the stored energy of C2 will be used to supply U1 for some time, reducing the influence of R1 to the timing.
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1. No - that's actually a KiCad 'power rail' flag to tell the DRC the power pin of U1 is actually connected to a power supply
2. Not quite, but getting warm. R1 limits the current through the diodes. This would end up in C1 anyway if D1 wasn't there. R1 needs to be as large as possible to avoid affecting the oscillation time. According to the data sheet it isn't actually large enough. Frequency of oscillation - which isn't that critical anyway - was established experimentally. You want to keep C2 as small as possible for a given frequency, as the charge it holds at the end of each cycle is wasted! The oscillation frequency is actually pretty stable despite ambient temperature and supply voltage changes, even though it isn't doesn't matter much.
--- Quote from: tggzzz on June 25, 2022, 09:25:15 am ---
--- Quote from: nfmax on June 25, 2022, 08:09:26 am ---A special bonus point to the first person to correctly describe what purpose D1 serves
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I wish all schematics were as well laid out and informative as that!
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We try to do our best! 8)
--- Quote from: tggzzz on June 25, 2022, 09:25:15 am ---I guess D1 prevents SCR latchup when there's no battery and the voltage across C1 decays.
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Nope.
4000B CMOS is specified down to 3V supply. Which means that both the P & N device thresholds must be less than that. So at 6V supply or thereabouts, both can be on at the same time, when the input to a gate is at around mid rail. This happens at pin 11 twice every cycle of the oscillator. With fresh batteries, this takes a significant and unnecessary gulp of charge from the supply. D1 drops just enough voltage to significantly reduce this, while, unlike a regulator, dissipating no standby power.
Note there is no capacitor at U1 pin 16. If you put one here, it will happily supply the unwanted gulp, and charge itself back up during the rest of the cycle. Bad capacitor! But 4000 CMOS is slow enough not to absolutely require decoupling directly at the chip.
As I said, 4000 CMOS is cool!
Saskia:
not joining discord, you'llforgive me
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