Reddit:Electronics

18 pair cable from a Toshiba CT scanners got cut... somehow...

Was at the Super Bowl (a bit drunk ngl) and the hole for the RF control was to the left of the actual LEDs, I can’t stop wondering if I could turn it back on if I had the right equipment.

The LEDs also looked a bit strange, not like the normal ones I see.

Thank you for everyone’s encouragement earlier and it was cool to read about other peoples mistakes! I finally got my z80 build going - 4mhz beast underclocked to 1mhz for stability and its running best OS out there - BASIC. I really would love to add proper video and audio output next, for a moment serial it is.

There was a lot I learned, but this was my first serious project in which I went double over budget, went over my deadline and had a lot of fun! It has 8 potentiometers, 4 inverters, 3 integrators, 2 adders, a multiplier and some. In the first image, it is running damped oscillation, which is simulating something like a mass to a spring. Here is the build on my website if anyone is interested https://paranoidrobot.neocities.org/Analogcomputerbuild

Just finished my first PA and did a sound check. Used Rod Elliott' P3A schematic but didn't order the PCB's, made my own looking at the component placement he chose. Also did the P33 DC protection and muting circuit from the schematics on his website, also my own PCB design. Ordered a BT module from Aliexpress that worked out great. Did the PCB design in KiCAD and etched the boards. Got screwed on the final transistors, found out they weighed 3 grams less than the originals so ended up ordering other ones from a supplier in Europe. Also the 10.000uF caps were counterfeit and ordered other ones.

The toroidal transformer is from Aliexpress from one of those custom order vendors. Had to do an additional source for the BT module to avoid hum/ground loops.

Here's how it sounds:

https://youtu.be/3uhvbGdac8s?si=9sRjmpB0z5sSqoV8

Had a lot of fun building it. Can't wait for the next project! 😄

Esp dap

So yeah this is starting to look like a bit of a monster

Man that program was fun! Engineering C building ftw!

In the Astron schematic dated 1987, the violet arrow points to an error in the drawing. It shows the 29 VDC rectified power being routed to the Base connections of Q101 - Q104 series pass transistors. Compare this to the XX-35 series supplies dated 2000. The schematic with the error was found on the internet, but thus far I have not been able to retrace the path to the page of the schematic with the erroneous connections.

Here is a link to the Service Manual for the series: Astron RM-35A, RM-35M, RS-35A, RS-35M Service manual

I spent few days trying to make z80 cpu based computer clone. As in every good project first step was performing Hello World output to serial for starters. I got completely stuck as I was getting only letter H and nothing else. I rewired chip selection logic several times, replaced RAM chip, scoped everything I could and only then noticed that top power rails are not connected (you can see top rails are not bridged) meaning RAM was never powered in a first place. I feel like a complete moron…

Having a particular plan for the power supply (as described in the posts before part 2 - Planning and part 1 - Idea) it's possible to start schematics itself. I use and really enjoy KiCAD - it has everything I need for my skills and projects I create.

As the first step with the schematics (see - github.com/condevtion/i2c-pps-hw) I decided mostly to transform the diagram from the previous post to a set of pages and define networks and busses to connect them. You can see a screenshot of the root page in the first picture with the result. The second picture contains everything from the rest of the pages. It's not much for now - the controller's symbol, and a bunch of network and hierarchical labels to enable so called "sheet pins".

I made the symbol starting from one for BQ25798 existed in KiCAD's global library. The chip is quite different but it can be easily transformed by majorly editing pins. While the footprint and 3D model can be requested from Ultra Librarian site by like provided on TI page for BQ25758S. All symbols and footprints I usually add to local projects libraries just not to mess with global library.

In KiCAD its a bit tricky to create nice, short names for busses. You need to create aliases in "File" > "Schematic Setup" > "Bus Alias Definitions" and then you can use them across all pages of a project. For now I came up with following networks and busses:

• VIN - positive input voltage. The master switch page should contain an input connector and protection circuit (fuse, TVS diode) after which the network starts. As well is used to power the digital I/O and indication block
• VINP - positive input voltage after the master switch itself (goes to the input filter)
• EN - master switch control signal (should be high to turn the switch on and low to turn it OFF)
• VINN - output of the input filter
• VOUT - the output voltages bus (contains power stage output and whole device output networks, goes to the output filter)
• CSIN - the input current sensor bus (goes to ACN and ACP pins of the controller)
• CSOUT - the output current sensor bus (goes to SRN and SRP pins)
• I2C - I2C bus itself (connected to SCL and SDA pins)
• GPIO - groups digital I/O lines: interrupt, power good, status, and chip enable
• PROG - groups the rest of analog input lines which should be connected to the programming block to set operating mode and limits for the controller Maybe, going through detailed design these will require changes.

The next step is to draft every page with actual design probably skipping at first particular values for components.

First and foremost what are reflections?

Reflections in PCB are like echoes on a road for electrons. Imagine a PCB trace (the thin copper line) is a highway. A signal is a tiny super-fast car zooming down that highway. Now…

If the road suddenly changes, the trace gets thinner or wider, it hits a connector or the layer changes, it’s like the car suddenly hit a speed bump or a wall. Instead of all the signal energy moving forward nicely, some of it bounces back. This bounce is a reflection.

Why does it happen?

Because of impedance mismatch.

If the trace impedance (say 50Ω) suddenly meets something that is not 50Ω, the signal doesn't have enough voltage or current to pass through and reflects back.

What are the three types of impedances a signal encounters?

Source impedance, Characteristic impedance and Load Impedance.

• Source Impedance (Zₛ) : This is the output resistance of the driver. It's what the signal encounters at the chip pin sending the signal (before it's launched onto the trace). Inside that chip, there’s some internal resistance. That’s the source impedance.
• Characteristic Impedance ( Z₀): This is the natural impedance of the trace itself. This is NOT resistance like a resistor. It’s the ratio of voltage to current for a wave traveling down the trace. Which is affected by the trace width, thickness, distance to ground plane (return path), dielectric material etc.
• Load Impedance (Zₗ): This is the input impedance of the receiving device. It’s the chip pin at the other end of the trace. The load decides what happens when the signal arrives.

The Golden Rule (No Reflection Condition)

Maximum happiness is achieved when:

Zₛ = Z₀ = Zₗ

What happens when one is higher or lower than the other?

Now we’re getting into the “who wins the fight” part of signal integrity.

Case 1: Z₀ > Zₛ (Trace impedance is bigger than source impedance)

The source is “stronger” (lower resistance) than what the trace expects. When the signal hits the load and reflects back, the reflection at the source will be positive. That means, the returning wave adds to the original signal, we will see overshoot and possible ringing as well. We may see the waveform jump higher than it should before settling.

Case 2: Z₀ < Zₛ (Trace impedance is smaller than source impedance)

Now the source is “weaker” compared to the trace. When the reflection returns to the source, the reflection at the source becomes negative. We may see undershoot, slower settling and reflected wave subtracting from the signal. The signal may dip below expected levels before stabilizing.

Image Credits: Right the first time by Lee Ritchey . Best book I have read on signal integrity and design.

I was trying to identify some IC's recently and found out that ChatGPT is incredibly good at identifying IC parts from their markings with some extra context information.

It can require some prodding and trial and error and giving it some hints helps e.g. a description about what you think it does, component footprint, visible marking, the device you found it on. and force it to list number of alternatives. You can also give it a picture and let it find the layout context.

Example I was trying to identify the component marked: KP05 5MES. I gave it the picture and the prompt:

""
Help me find this component: The packaging has these markings:
KP05 5MES
It has aSOIC-8 package
It is a high speed component that operates in the GHz range.
Found on the front end of a GigaWave 6400
Give me a list of possible alternatives.

""

One of the suggested components is the MC10EP05 and I could then verify it by looking at the datasheet

That's pretty cool