Electrical Engineering

A place to talk with friends from the EE community about vacuu...
Wed 17:24
@uhoh waterjet could cut/drill it; unsure about small holes though
Jul 17 12:06
nearby GSM sounds like better routing/placement/shielding may be the best solution
Jul 17 12:05
which type of microphone?
Jul 15 15:08
Repairing a unit which features a copper snubber bus bar. Normally they are bright and clean. This unit popped some SCRs, which threw enough exotic substances into the enclosure that the copper bar now looks quite weathered and corroded
Jul 15 13:26
it's too bad one can't make an "aqua-regia" of paint-solvents, like can be made with acids
Jul 15 13:24
*it heheh
Jul 15 13:24
I seem to recall that it may be a polyurethane formulation that is solderable, rather than enamel. Been a long while since looked into tit
Jul 15 13:06
Enamel might be easy to remove with the right solvent - cotton ball, twist, pull, solder? Haven't tried that
Jul 15 13:00
That magnet wire is quite elusive... have seen it used, but never seen a source. Could also try a tiny torch and regular enamel wire; fast but still needs a few pulls of scotch-brite or sandpaper to make the result solder-friendly.
Jul 10 13:42
It could go like this - setup µC to match device, connect (suggest low-speed breadboard or dead-bug initial development), discover it will not communicate; end up following the device datasheet timing (with a scope - logic analyzer hides parasitics), only to find that some edge is not where the datasheet wants it (by some nanoseconds) or transitions too slowly/quickly, etc.
Jul 10 11:47
Re: EEPROM - threw in the towel. OEM utilized a checksum, which when wrong, would prevent it from being firmware-updated. Since all had bit-rot, none could be reloaded
Jul 10 11:45
You can think of SPI as Chrysler, I2C as Ford, etc. It may be a "standard" but there are certainly a lot of differences in implementation. Ran across more than a few SPI devices that needed special tweaks.
Jul 8 19:17
of course not lol
Jul 8 18:53
wondering what'll happen if I just try a blanked eeprom in it... wonder the chances of it saying "whoa, first power-on, let me provision that for you..."
Jul 8 18:47
Analyzing how I think parameters are stored on the EEPROM (min, max, value), have found a few cells where max should have been FF and was instead 00 - not explainable from bit-rot. Software complains when factory-defaulted - min/max limit violated
Jul 8 15:52
Was able to deduce that 0x1FFE should be 0x12 - now have the device being recognized properly, but there are other errors still
Jul 7 20:08
Apparently bits which "rot" return from logic 0 to logic 1. So, if you read a byte multiple times and some of the bits consistently read as 0, those are definitely zero. It's the bits that were 0 that are now 1 which are the issue.
Jul 7 19:43
Another Q about bit-rot in that EEPROM - will it tend to have more 1-to-0 errors, 0-1, or completely random?
Jul 7 14:54
Some difference in this area is causing the device to not even be detectable... was thinking that the last two bytes may be CRC and null, but even that isn't making sense
Jul 7 14:54
Being an EEPROM, there are intentional differences between the files, as parameters would be different between the units. But the 64 bytes highlighted is specifically the "device identification" area of this EEPROM, which can only be R/W by raising a pin to 12v.
Jul 7 13:56
"new" meaning just-ripped - all EEPROMs are old and subject to bit-rot
Jul 7 13:55
Highlighted is the "identification" area, 64 bytes. Left file is new, middle gives "device unknown" and right doesn't even see the device - trying to figure out which bits if any are corrupt in left.
Jul 7 13:54
Jul 7 13:52
On a different note, have a question about this AT28C64B EEPROM. Claims data retention of 10yrs. Seeing devices losing their data after 20yrs. No original code. Comparing 3pcs, trying to see which bits are corrupt. Is there any rhyme-or-reason as to which bits rot first?
Jul 7 13:41
bean counters will be up in arms :)
Jul 7 13:41
use 1% resistors for R2 and R3 if possible
Jul 7 13:35
that's very possible as the ends of the pot travel are very non-linear
Jul 7 13:33
likely. could try instead of A1 above, injecting the 0-5V output into R1 and see how the circuit handles it - might be too "hot" still (increase R1) or non-linear (go with the amp)
Jul 7 13:30
any idea what the input impedance is of the existing circuitry?
Jul 7 13:27
oh no wait, read that wrong - existing joystick is centered at 2.5v with span to 5v and 0v - target is 2.5v +- 0.6v; can totally do that with resistors
Jul 7 13:22
but 2.5v input won't give 3.1v output with passives alone - could use a cap as a charge pump, but then that'll drift... kinda requires an amp or level-shifting of some sort
Jul 7 13:06
What frequencies of interest? The square-er the transitions needed, the higher the harmonics go; fast edges would require a very fast amp. Can't use passives since the target output voltage is 0.6v above input max voltage (2.5v).
Jun 5 17:32
Had the (mis)fortune of soldering some prototype LGA-109 components once... essentially a tiny PCB with pads on the bottom... had a ~75% success rate, ironically hindered by the "no-clean" flux in the paste. Higher voltages and RF stuff was no problem, but the 5v logic liked to be "lossy" or worse on several boards.
May 16 15:49
I'd asked LT once if I could draw 10uA from a RS232 IC's -5v rail. They of course couldn't answer concisely, except to say that it isn't recommended but would likely work. It indeed worked fine.
Apr 15 14:48
In my neck of the woods, there's an optional year of preschool (parent-funded), then 'kindergarten' through 6th year of elementary school, two years of 'middle school', and four years of high school. Parents can send their kids to public school (paid for by taxes), or private school (paid for by parents.) Then college.
Apr 14 19:37
But it is not a requirement to "change majors."
Apr 14 19:36
Lundin, my experience from the 'states is that Highschool offers "electives" after the basics are complete. So one could take engineering classes if they like. But if not, most "College" or "University" offer equivalent classes - for a price. College is quite expensive, and the best ones are very costly, difficult to get into, and have a lengthy wait-list.
Apr 11 13:01
half of these jokes are doped; the other half have serious holes in them.
Mar 26 12:05
Random fact of the day... coffee beans contain "bad" cholesterol-raising compounds. Paper filters are fine enough to trap these, while metal mesh filters are too coarse. There can be a 30x decrease in concentration just by using a paper filter.
Jan 24 01:44
Probably could Nick, but these are some rather unusual devices (Carel HVAC controllers). Apparently the customer's programmer works for them; I don't have one of those, so was trying different chips to "talk" to it. Just good to know that 3.3V transceivers exist and may not be compatible with 5v.
Jan 23 13:43
It even has the feature of being self-powered from the RS232 interface (or external 12V, or internal batteries.)
Jan 23 13:43
BTW, if trying to talk to a 3.3V RS485 transceiver, this particular adapter does work: advantech.com/en-us/products/…
Jan 21 21:54
BTW, ran across a ti.com/lit/ds/slls505p/slls505p.pdf?ts=1737398834372 3.3V RS-485 transceiver. It would NOT communicate with a standard 5V model (TX signals too low.)
Jan 21 20:32
Tobalt, perhaps you've seen this: community.st.com/t5/stm32-mcus/…
Jan 21 20:04
Nice, thank you. Of course, dealing with an obscure (custom) motor and no diagram. We'll know soon :)
Jan 21 19:17
If a 240VAC, 400W capacitor-run blower motor has two windings, 209mH @ 73R and 147mH @ 53R, which winding is the capacitor-run winding? Any way to tell?
Jan 21 19:16
UART receive in general can be quite tricky.
Nov 6, 2024 13:57
sounds like roll-your-own is the best bet here
Oct 22, 2024 13:48
@misk94555 Laptop TRS output is maybe 1vpp into 16 Ohms, but this can vary wildly. Put a 32R across an output, 'scope it, then a 16R. From the difference, estimate the impedance. Or if you can examine the output circuitry, derive from that.
Oct 14, 2024 01:27
Also consider the leakage current of those 4x 330uF caps; 100uA on the secondary side will draw at least (26/6*100uA) = about half a milliamp.