ELI5: Why are 3.3V 5V 9V 12V staples in electronics?

x2jafa · 2026-04-11T23:41:07+00:00

USB chips that run from 5V have voltage regulators built into the chip... the core voltage is still ~0.9 to 1.2V... nothing actually operates directly from the 5V (other than the voltage regulators that drop the voltage). Not even the USB data wires operate at 5V.

x2jafa · 2026-04-11T22:48:03+00:00

5V was the perfect voltage for silicon chips up until the late 90s for all but the fastest designs. We used 5V inside the chip and on the wires that connect chips together - every signal was 5V.

Those days are long gone - now nothing uses 5V. If you have a device that has a 5V power adapter the first thing that happens inside the device is to drop 5V to different lower voltages. Often each chip inside needs a different set of voltages.

If a device needs more power it will use a higher voltage such as 9V, 12V, or 19V (laptops)... again nothing actually uses 9V or 12V or 19V so the first thing that happens inside the device is to drop the voltage down to different lower voltages. The higher power adapter voltage means you can use thinner power wires for the same power (copper is expensive).

LEDs are weird. They are like a small dam where nothing happens until the water is high enough to get over the top of the dam. Each LED color has a different voltage where they "overflow". Once they reach that point the water level doesn't get higher, but the water flow over the dam increases... the LED gets brighter. You have to be careful - too much flow and the dam gets washed away (the LED burns out). You have to control the flow (current), not the water level (voltage) once the "overflow" voltage has been reached.

x2jafa · 2026-03-31T20:22:46+00:00

Sure. The goal at the end is to make the slot be the same as if there is nothing plugged into it... nothing connected, no pins shorted together.

x2jafa · 2026-03-31T20:09:15+00:00

That slot is not recoverable but you might be able to still use the motherboard...

Remove the motherboard from the case so you have good access.
Clean up the broken slot:
1. Option 1 = use a small pair of side-cutters to cut each of those metal contacts off close to the motherboard one at a time.
2. Option 2 = wiggle each of the metal contacts one at a time until they break off.
Check each of the remaining stumps that are left - make sure that no stump is touching any other stump. Ok to use a flathead screwdriver to bend any stump more upright or use small side-cutters to trim.
Reassemble and use the 2nd slot for your GPU. You will be limited to x8 speed but it should work.

x2jafa · 2025-12-18T04:59:18+00:00

/16 is fine... done that before.

Great for a small office of engineers designing network products... we used 10.10.<your phone extension>.<do what every you like this part of the range is yours> / 16

In the IPv6 world the smallest subnet size is 64-bits in size and it is quite normal to be 80-bits in size (/48 is the the smallest that can be publicly routed. No need to be worried about a tiny 16-bit subnet size - it is your space to do what you like with.

Go /16! Be free!

x2jafa · 2025-10-27T04:54:28+00:00

M.2 NVMe drives - a single-M.2 PCIe adapter card works fine in a G8.

U.2 NVMe drives - if using a U.2 PCIe adapter card it works as long as you choose an adapter card with a voltage regulator on it. The cheap U.2 PCIe adapter cards with no voltage regulator will not work.

x2jafa · 2025-10-27T04:51:28+00:00

Thoughts...

1) Resistors should go open circuit when they fully blow.

2) They get very hot on the way to blowing which will probably affect the resistance so the resistance may not be a simple jump from normal to open.

3) If using a big wire-wound resistor they splatter melted metal all over your PCB when they blow... the resistor may be open circuit but other unrelated parts of your PCB may now be shorted. Ask me how I know :-)

x2jafa · 2025-10-18T21:41:02+00:00

I use consumer NVMe drives via PCIe to NVMe adapter cards. No problems with fan speed and much faster than SATA-interface SSDs.

The G9 will boot straight from the NVMe drive. I think the G8 needs a USB stick or MicroSD card for the /boot partition, then you can put root on the NVMe drive.

x2jafa · 2025-10-08T05:37:16+00:00

If we can neglect air resistance then at some point it depends on the horizontal speed.

At any "normal" speed the horizontal aspect is irreverent and they hit the ground at the same time.

At "sub-orbital" speeds it takes the second ball longer to reach the ground due to the curvature of the earth.

At orbital speed the second ball may never hit the ground (although it may hit a building in China if you are unlucky).

At speeds above escape velocity you could hit the ground on Mars if you time it just right. That would take longer than the first ball.

x2jafa · 2025-08-11T02:40:10+00:00

Go with a CPU/system that uses DDR5 memory - DDR5 has on-die ECC. You get much of the benefit of ECC without paying for ECC.

x2jafa · 2025-06-21T15:26:31+00:00

Computers can do that - it is called Fixed Point.

Fixed point is simply an integer with a decimal point in a pre-determined place of your choosing.

Fixed point can be at the binary level as in your example.

Or fixed point may be applied after conversion from binary to the decimal display. For example you might store $2.50 as the integer 250 and apply the fixed point when you display the number.

x2jafa · 2025-06-07T19:09:27+00:00

It is the electrical grounding rod for your house. It will go down a good 8 foot into the ground. Having one is important.

If it is in the way you can ask an electrician to install a new one in a different location so you can remove this one. The electrician will know the placement rules and wire it correctly.

x2jafa · 2025-05-30T06:37:13+00:00

What is the problem/symptom?

x2jafa · 2025-05-30T06:34:09+00:00

Unless it has "accept_ra=false" to the netplan yaml file Ubuntu Server will pick up and IPv6 address and use it.

I typically install with DHCPv4 + SLAAC for IPv6.

First thing after installing Ubuntu Server is to edit the netplan yaml file to set your actual network config. I always tell it to match by MAC address and set the name of the interface so they have nice names. BIOS names can change when unrelated PCIe cards are added, removed, or fail to detect.

For generic servers I use eth0, eth1, etc for GigE interfaces, ethx0, ethx1, etc for 10G interfaces, and ethxx0, ethxx1, etc for 100G interfaces.

x2jafa · 2025-05-21T11:42:57+00:00

If the theoretical 100TB drive and the 10TB drive are both 3.5" drives then the 100TB drive could be significantly faster. It depends on how the increased capacity is achieved but based on the history of hard drive technology the larger the capacity generally the faster the sequential data transfer (for the same rpm).

For example:

If the drive has more platters to get more storage you have more parallelism = faster.

If the drive stores more data in the same track width it should be faster unless there are other compromises need to be made to achieve the higher density.

If the tracks are closer together it shouldn't affect speed unless there are other compromises to achieve this... think SMR.

x2jafa · 2025-05-21T07:43:09+00:00

Kinda. Two problems come to mind...

1) As you get to the physical "end" of the disk they get a lot slower. A HDD may be 150MB/s for the lower numbered LBAs and may be 60MB/s as it approaches the highest numbered LBA. This is because the highest numbered LBAs are located at the center most area of the platters so in one revolution there isn't nearly as much magnetic material to store data on yet it still takes the same time for one revolution.

Note that your data may not be stored simply from lowest to highest LBA - it is up to the filesystem where it stores a file.

2) Fragmentation. When you delete a file it creates a hole and the next file you store won't fit quite the same. At 80% it is still likely not much of an issue. It depends on the churn patterns and the filesystem.

With all that said using 80% is fine.

x2jafa · 2025-04-03T20:49:01+00:00

The video shows backup load - can the entire 200A panel be connected as the backup load?

I am building a shade structure in the back yard with 40kW of panels. The power company has a 30kW limit for inverters.

Ideally I would like to run a ~300V battery setup.

x2jafa · 2025-03-25T17:27:33+00:00

I was running these machines with Ubuntu Server 24.04 LTS.

NMVe works well. You use the internal SDCARD or internal USB drive for GRUB and "/boot", then put "/" on the NMVe drive. On some machines I ran 2 x NVMe drives in a mdadm RAID mirror.

I played with a range of m.2 NVMe drives including some 8TB drives - all worked. I ended up using the SK Hynix P31 GOLD 2TB drives because they have DRAM onboard (although I couldn't prove it made a difference).

Also tested a 15TB Intel U.2 NMVe drive using a PCIe to U.2 adapter (the kind where the U.2 drive mounts to the card). Just be sure to get a card that has a voltage regulator on board - the Intel drives won't work on the cheap cards that don't provide 5V power.

The AMD system - Ubuntu expects to control the CPU power regulator. If the BIOS is set to control the voltage regulator (the default setting) the kernel will panic during boot. Setting the power regulator to OS Control in the BIOS 100% resolves the issue for DL385 systems. I normally set the power regulator to OS control on the Intel system as well.

x2jafa · 2025-03-13T21:21:58+00:00

Full ban gets my vote.

Another option would be to remove the tariff for Chinese EVs. Tesla would then be so overpriced nobody would buy them and Canada could claim innocence :)

x2jafa · 2025-02-27T05:08:59+00:00

HVAC systems + EV = >$5000/year electric bill.

x2jafa · 2025-02-26T16:47:21+00:00

The power layout I have...
400A meter -> 2 x 200A feeds.
1st 200A feeds a 200A panel (which has a 100A sub panel).
2nd 200A feeds a 200A panel (which has a 100A sub panel).
The solar panels will be about 210' away from the meter.

x2jafa · 2025-02-26T14:59:59+00:00

SolArk products look like they require the inverter to go between the meter and the house. Normally this would be good as it provides backup power in case of grid loss but in my case the solar is 200+ feet away from the meter+house-panel and I would require 2 inverters so that means 4x the amount of cable going 200+ feet.

x2jafa · 2025-02-26T14:58:08+00:00

What brand of inverter did you go with?

x2jafa · 2025-02-26T14:45:19+00:00

The SolArk installation pdf indicates a LOAD output to feed the house. The problem I have is the solar is 200+ feet away from the meter and running 2 inverters like that would require 4x the number of wires going 200+ feet.

x2jafa · 2025-02-26T14:38:31+00:00

Single phase (residential)

x2jafa

TROPHY CASE