Gus
@projectgus@aus.social replied  ·  activity timestamp 3 days ago

This is a cheap USB 3.0 interface card I bought on eBay (real vs seller's photo). I picked this one because it would have the fastest shipping to me, but now I have some regrets.

Differences spotted include:

- PTC fuses vs 0 ohm resistor jumpers
- Most of the bulk caps missing
- Ceramic decoupling cap is totally missing on one of the ports (!)
- Two DC/DC converters vs one

Now taking bets on whether this thing works, and/or how noisy and flaky it is. (My bet is all three - works but also sucks)

#electronics
niconiconi
@niconiconi@mk.absturztau.be  ·  activity timestamp 6 days ago

Cirno's Math Class awa : SOL Calibration for Dummies #electronics

In one-port measurements, a VNA's measurement readings contain linear errors. One can represent the Device-Under-Test (DUT) as a cascade of an irremovable two-port error network (Error Box) and the true DUT. The true reflection coefficient Γ is modified by Error Box into the imperfect reading Γ′.

The Error Box represents both the signal path errors (e.g. mismatch reflection, electrical delay/phase shift) and VNA's internal receiver errors. Like all two-port networks, one can define it using 4 S-parameters: S₁₁, S₂₁, S₁₂ and S₂₂.

Using the standard formula to cascade a 2-port and a 1-port network, we find the measured reflection coefficient is:

Γ′ = [S₁₁ − (S₁₁S₂₂ − S₂₁S₁₂)Γ] / (1 − S₂₂Γ)

All four S-parameters of the Error Box are mixed with the DUT's reflection coefficient Γ, including a difficult cross-term (S₁₁S₂₂ − S₂₁S₁₂) - apparently making them unsolvable. But we only care about the overall error, not individual terms. Thus we can linearize the equations as such:

m₁ = 1 x₁ = S₁₁

m₂ = ΓΓ′ x₂ = S₂₂

m₃ = −Γ x₃ = S₁₁S₂₂ − S₂₁S₁₂

The left-hand side is fully known, because they only contain known measurement reading Γ′, and the DUT's true reflection coefficient Γ - which is known when for characterized calibration kits.

Notably, there are only 3 out of 4 variables left. Intuitively, it means that both the forward (Port 1 to Port 2) and reverse path (Port 2 to Port 1) in the Error Box can attenuate a signal. They're indistinguishable by one-port measurements alone, so there are three effective error terms only. Some papers assume reciprocity (S₁₂ = S₂₁) or explicitly normalize one variable away (S₂₁ = 1).

Substitute the variables in the original equations, we obtain a linear equation:

Γ′ = (x₁ − x₃Γ) / (1 − x₂Γ)

Γ′ − ΓΓ′x₂ = x₁ − Γx₃

Γ′ − m₂x₂ = m₁x₁ + m₃x₃

Γ′ = m₁x₁ + m₂x₂ + m₃x₃

When we have three calibration standards with arbitrary reflection coefficients Γ₁, Γ₂, Γ₃, and three imperfect measurement readings Γ₁′, Γ₂′, Γ₃′ (such as Short, Open, Load). We have a linear system of equations with three unknowns, a standard high-school math question.

m₁₁x₁ + m₁₂x₂ + m₁₃x₃ = Γ₁′

m₂₁x₁ + m₂₂x₂ + m₂₃x₃ = Γ₂′

m₃₁x₁ + m₃₂x₂ + m₃₃x₃ = Γ₃′

Once solved, x₁, x₂ and x₃ can be plugged into the first equation to find the perfect Γ from Γ′ for all future measurements.

Note how Γ₁, Γ₂, Γ₃ need not to be perfect, just be known. This only practical requirement is that they must maintain a distance from each other on the complex plane. If two measurements are too close, the system is ill-conditioned since an equation has been lost. Short and Open are common choices because they are always 180° away ideally.
niconiconi
@niconiconi@mk.absturztau.be  ·  activity timestamp 6 days ago

Cirno's Math Class awa : SOL Calibration for Dummies #electronics

In one-port measurements, a VNA's measurement readings contain linear errors. One can represent the Device-Under-Test (DUT) as a cascade of an irremovable two-port error network (Error Box) and the true DUT. The true reflection coefficient Γ is modified by Error Box into the imperfect reading Γ′.

The Error Box represents both the signal path errors (e.g. mismatch reflection, electrical delay/phase shift) and VNA's internal receiver errors. Like all two-port networks, one can define it using 4 S-parameters: S₁₁, S₂₁, S₁₂ and S₂₂.

Using the standard formula to cascade a 2-port and a 1-port network, we find the measured reflection coefficient is:

Γ′ = [S₁₁ − (S₁₁S₂₂ − S₂₁S₁₂)Γ] / (1 − S₂₂Γ)

All four S-parameters of the Error Box are mixed with the DUT's reflection coefficient Γ, including a difficult cross-term (S₁₁S₂₂ − S₂₁S₁₂) - apparently making them unsolvable. But we only care about the overall error, not individual terms. Thus we can linearize the equations as such:

m₁ = 1 x₁ = S₁₁

m₂ = ΓΓ′ x₂ = S₂₂

m₃ = −Γ x₃ = S₁₁S₂₂ − S₂₁S₁₂

The left-hand side is fully known, because they only contain known measurement reading Γ′, and the DUT's true reflection coefficient Γ - which is known when for characterized calibration kits.

Notably, there are only 3 out of 4 variables left. Intuitively, it means that both the forward (Port 1 to Port 2) and reverse path (Port 2 to Port 1) in the Error Box can attenuate a signal. They're indistinguishable by one-port measurements alone, so there are three effective error terms only. Some papers assume reciprocity (S₁₂ = S₂₁) or explicitly normalize one variable away (S₂₁ = 1).

Substitute the variables in the original equations, we obtain a linear equation:

Γ′ = (x₁ − x₃Γ) / (1 − x₂Γ)

Γ′ − ΓΓ′x₂ = x₁ − Γx₃

Γ′ − m₂x₂ = m₁x₁ + m₃x₃

Γ′ = m₁x₁ + m₂x₂ + m₃x₃

When we have three calibration standards with arbitrary reflection coefficients Γ₁, Γ₂, Γ₃, and three imperfect measurement readings Γ₁′, Γ₂′, Γ₃′ (such as Short, Open, Load). We have a linear system of equations with three unknowns, a standard high-school math question.

m₁₁x₁ + m₁₂x₂ + m₁₃x₃ = Γ₁′

m₂₁x₁ + m₂₂x₂ + m₂₃x₃ = Γ₂′

m₃₁x₁ + m₃₂x₂ + m₃₃x₃ = Γ₃′

Once solved, x₁, x₂ and x₃ can be plugged into the first equation to find the perfect Γ from Γ′ for all future measurements.

Note how Γ₁, Γ₂, Γ₃ need not to be perfect, just be known. This only practical requirement is that they must maintain a distance from each other on the complex plane. If two measurements are too close, the system is ill-conditioned since an equation has been lost. Short and Open are common choices because they are always 180° away ideally.

alcinnz
Joel Michael
alcinnz and 1 other boosted
Gus
@projectgus@aus.social  ·  activity timestamp 2 weeks ago

"Candle Flame Oscillations as a Clock" - wow!
https://cpldcpu.com/2025/08/13/candle-flame-oscillations-as-a-clock/

#electronics #ch32v003

Animation of three candles flickering at approx 10Hz, next to an LED blinking at 1Hz
Animation of three candles flickering at approx 10Hz, next to an LED blinking at 1Hz
arclight
@arclight@oldbytes.space  ·  activity timestamp 2 weeks ago

Want an easy soldering project and detailed project and firmware notes so you know what you're building? Try the TV-B-Gone! https://www.tvbgone.com/shop/tv-b-gone-kit-universal-build-tv-b-gone-kit/

Adafruit posted design notes for the kit and there are interesting tidbits on reverse engineering an IR signal, compressing the IR codes to fit nicely into an ATTINY microcontroller, and preserving LED lifespan by not driving them so hard: https://learn.adafruit.com/tv-b-gone-kit/design-notes

I kind of want one with a mute feature too. #electronics #selfcare
arclight
@arclight@oldbytes.space  ·  activity timestamp 2 weeks ago

Want an easy soldering project and detailed project and firmware notes so you know what you're building? Try the TV-B-Gone! https://www.tvbgone.com/shop/tv-b-gone-kit-universal-build-tv-b-gone-kit/

Adafruit posted design notes for the kit and there are interesting tidbits on reverse engineering an IR signal, compressing the IR codes to fit nicely into an ATTINY microcontroller, and preserving LED lifespan by not driving them so hard: https://learn.adafruit.com/tv-b-gone-kit/design-notes

I kind of want one with a mute feature too. #electronics #selfcare