Tech Forum

A Google search produced the following: https://www.rs-online.com/designspark/a-raspberry-pi-vax-cluster

Consider looking at SimH. It has a network-capable VAX Simulator. It is available in source code form (say, if you wanted to run it under Linux on an SBC), and also as a windows executable (you would not have to have use a virtual machine). Visit http://simh.trailing-edge.com/.

What you are looking for is SimH, a free VAX emulator that will run on the Raspberry Pi available at http://simh.trailing-edge.com/ You can get VMS licenses and software at www.openvmshobbyist.com/ Check out this article: https://www.rs-online.com/designspark/a-raspberry-pi-vax-cluster I think you will find everything you need.

I did a search for VAX VMS emulator and found the following: VAX/VMS on RaspberryPi at the RaspberryPi Forum - https://www.raspberrypi.org/forums/viewtopic.php?t=7552&p=93217

Crowns are generally great amps, very few issues. My guess is you have a cracked or weak solder joint someplace, perhaps in the power stage, that makes better contact once things get hot and expand. It might also be a bad cap somewhere, but that seems less likely to me.

You mention the model is DC150A. Crown does not list that model but does have a D-150 and D-150AII listed.

Service info is here https://www.crownaudio.com/en/products/d-series.

The symptom you mention could be crossover distortion in the output stage due to an out of spec bias voltage (very low or non existent). As the amp warms up the bias voltage generator begins to function to some degree and the distortion becomes less. The bias voltage is designed to vary as the output stage temperature changes but should never fall to zero.

Connect an audio generator (1 KHz, variable 0 to about 2 V RMS sine wave) to the amps input and connect a suitable sized dummy load (8 ohm) resistor and oscilloscope to the output terminals. Power up the amp and observe the output sine wave for distortion at the zero crossing. Also look for a symmetrical sine wave amplitude. An offset step at the zero crossing is likely a bias problem.

A non symmetrical sine wave could be a power supply problem or output transistor problem. If the sine wave is clipped on the top (well before maximum output power is reached) but the zero crossing point seems ok then the bias may not be the issue. Rather, the power supply voltage could be too low or the distortion is being introduced at the input stage or possibly the VA (voltage amplifier) stage.

One can often use a controlled burst of freeze spray to hit individual components once it has warmed up. Hitting resistors or capacitors, or even solder connections may reveal the culprit.

Motor soft-starters have become so common that there is even a Wikipedia article about them. Just look in the catalog of the nearest industrial electric supply and buy the size you need.

Yes, 3 phase motors can be soft started and such start controllers are readily available.
Two companies that offer them:

www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/AutomationandControl/ContactorsStarters/SoftStartersControllers/index.htm

www.baldor.com/brands/baldor-reliance/products/drives/ac-drives/soft-starter

There are many distributors that sell soft start controllers online, just do a search for “3 phase soft start” in your favorite search engine.

The solution here is a devise called a torque arrestor. Google "well pump torque arrestor" for more information.

I recommend a commercial soft-start 3-phase motor controller such as one in the ABB Softstarter family. You can look through a catalog and technical information here: [url=http://new.abb.com/low-voltage/products/softstarters]http://new.abb.com/low-voltage/products/softstarters[/url]. DO NOT try to build one yourself. Experimenting with three-phase line power can lead to problems that cost more than a commercial controller. Another suggestion: Connect a stainless-steel line to your pump to make it easy to hoist. If you try to lift it via the pipe or the electrical cord the pump could separate and leave you in a hole, literally. (I have no connection with ABB.)

The transformer hum is due to loose steel laminations in the transformer core. The alternating magnetic field (60 Hz) sets up a vibration within the core that can also be considerably amplified by the enclosure, if the enclosure and transformer mounting happen to resonate.
Your enclosure material is not the actual problem. Try placing the transformer on rubber isolation cushions to isolate it from the chassis/enclosure. Rubber grommets work well for this. This may reduce the hum, however, this will not address the loose laminations within the transformer and it will still make some hum sound. I don’t think much can be done about that except replacing the transformer.
 

It could be the case, but it also could be the laminations in the transformer core itself rattling after warm-up. Remove it from the case and make a trial run with the bare transformer sitting on a insulated surface (plywood) to find out. Or wear headphones and ignore the noise.

Line-frequency transformers always hum because their core is made of laminated steel. Hum is more pronounced in inexpensive transformers where lower-grade steel is used and it is driven further into saturation on each alternating-current half-cycle. The hum that you’re experiencing is most likely acoustically coupled to the transformer enclosure into or onto which it is mounted.

Try to isolate the mechanical coupling — e.g., use rubber grommets around the mounting hardware.

What about using a variac with a standard full wave rectifier and large filter capacitors? The schematic lists several commercial components.

Several things to mention before any attempt at construction.

• Be aware that most variacs are not fully isolated, meaning the neutral on the mains supply is connected to the neutral on the output.
• Mechanical stops will need to be implemented on the control dial as not to exceed a 90 volt DC output and most likely on the low end to prevent the motor from stalling.

Here is the "wrong" answer to the problem: Harbor Freight sells a Router Speed Control for $20. Plug it in between the wall outlet and your tool. See if it does what you want. If not, take it back and they will give you your money back.

Why switch when you can easily “translate” or convert 3.3V logic signals to 5V logic signals, and vice versa? Sparkfun electronics sells small boards with level-conversion devices ready to go. I prefer Texas Instruments SN74LVC4245 24-pin small-outline IC (SOIC) devices because they can translate eight signals independent of each other.

You’ll need two of these ICs, one for 3.3V to 5V logic, and another for 5V to 3.3V logic. You can mount these SMT ICs on Schmartboard SOIC-to-DIP adapters. Other suppliers offer similar products but I find the Schmartboard adapters easiest to solder.

In my view, that is not really an up front issue. If I want to build a logic circuit, I have an idea of what I want it to do. Than I start looking for the required parts, making a list of what parts would work, and some of the basic specs such as its operating voltage, cost, footprint, availability, etc.

Sometimes most of the required parts are only available in 3.3V, and the decision is made. Sometimes they are available in 3.3 and 5V, but the 3.3V version is some difficult package I can’t solder. Sometimes I can’t find all required parts in the same voltage, and I end up implementing a logic level shifter, usually simple to build with 2 transistors and a couple of resistors.

Point I’m trying to make is that the decision to go with 3.3 or 5V is usually dictated by the design, not a starting point.

Laptops, by virtue of their portability, are far more likely to be infected by malware than other computers. Cafes with "free" wireless are perfect networks for dark-side hackers. Once they get their "kung fu" into the system, they essentially own it. Also, remember that the NSA has the manufacturers bake in the ability to turn on the microphone of a cellular phone, even while it's turned off. The government doesn't deny this. That's why almost all of the batteries are now glued into smartphones - removing the battery would prevent it. We would be naive to assume it's significantly different for webcams. Think of the tape is a low-tech low-priced protection method of last resort. We should all do the same.

He is. The camera can be disabled under the operating system since it uses a software driver to convert the signals into data. Just have him search for that driver file (visit the help page of the O/S provider) and rename it, move it, or delete it (ignore any O/S attempts to replace the driver). If he sells the laptop, a new O/S install will revive the camera driver.

I hate to say it, but your roommate is right.

As someone who builds gaming computers for a living, I can tell you that any computer that is connected to the internet, can be subjected to some sort of unauthorized access. That’s why we have things like Anti-Virus, Firewalls and other protective programs.

With that being said, your camera can very well be accessed from the outside. Your roommates tape solution is common and works effectively to keep unwanted eyes from seeing what you’re doing. However, you should know that if someone has access to your camera, they have access to your hard drives as well!

You can make it harder for someone to access your Network by having a WPK Passcode instead of a WEP Passcode on your router, and setting up a secondary computer as a stand-alone firewall.

Hopefully I have answered your camera question.

As they say, “Just because you a paranoid, doesn’t mean that they aren’t out to get you.”

Actually, like your roommate, I also keep tape over my camera when I don’t intend on using it. I’m not actually as worried about someone hacking into it as I am about accidentally turning it on without knowing. It could be really embarrassing to find out later that your cam was on and someone was watching via Skype or something similar without you knowing.

Having someone hack into the cam is certainly possible. But user error is probably more likely. Either way, why not be safe and blind the camera when not needed.

I searched my hard disc and found a chart for thermal resistance vs. heat sink area for a 1.5mm thick heat sink. 1.8mm is not much different from 1.5mm so I will use that. This chart ends at 500 sq. cm. so I will extend the line and estimate that the thermal resistance is 2 deg C per watt. I am also assuming the thermal resistance is in deg C/watt since it is not otherwise labeled.

Since the dissipation is 4.6 watts per TO220 and there are two of them, the power to the heat sink is 9.2 watts. The heat sink area is 34X20=680 sq. mm. The temperature rise in the heat sink is: 2 deg C/watt X 9.2 watts = 18.4 deg C. The temperature rise to the junction of the TO220 is: 6 deg/watt X 4.6 watts = 27.6 deg C. Adding these together, the junction of the TO220 will be 46 deg C above the heat sink temperature which will be above the ambient of nominal 25 deg C.

It is not possible to estimate the further rise of the heat sink due to lack of air circulation without more information such as size of the enclosure, thickness of the plastic, thermal resistance of the plastic, etcetera.

Circularly or elliptically polarized antennas are used to transmit to both vertically or horizontally polarized antennas to reduce flutter to or from a moving receiver, as mentioned by Don Pitchford. I've seen some local HDTV stations in the Washington D.C. area are now using elliptically polarized antennas and I've found I can receive these stations using either a horizontal or vertical antenna. So, in a moving car receiving the TV signal using a vertical antenna will work just fine. After all, it is much easier to install a vertical antenna on a car than a horizontal antenna is.

There is probably no need for you to install a circularly polarized antenna to receive circularly polarized signals, use either your vertical or a horizontal antenna, either should work just fine.

Google diy vhf circular polarized antenna. There are quite a number of hits. For example: http://ka7oei.blogspot.com/2013/08/a-circularly-polarized-omnidirectional.html.

You are very unlikely to encounter circularly polarized radio signals from local sources. Circular polarization is mostly used for receiving Low Earth Orbiting (LEO) satellites and stuff in the microwave and upper end of the UHF ranges. If you do find any of these signals they will have a distinctive rhythmic change in signal strength as the polarization of the signal changes; maximum as it matches your receiving antenna’s polarization, then minimum as it becomes opposite your antenna’s polarization.

If you have a receiver capable of covering the 145 MHz and 437 MHz ranges you may want to check out ham radio satellite sources such as https://www.amsat.org/fm-satellite-frequency-summary for information about receiving them.

As for receiving circularly polarized signals should you find any, if they are strong enough that the null in signal strength is still strong enough for you to hear it clearly, then you will likely not know the signal is circularly polarized and need do nothing special to receive it. For weak signals you will need to try both Right Hand and Left Hand circular polarization to determine which is needed, as the wrong circular polarization is worse than just using a linear polarized (in your case vertical) antenna.

If you want to learn more about circular polarized antennas https://www.e-education.psu.edu/geog862/node/1782 and https://rcexplorer.se/projects/2011/08/circular-polarization-explained have very good simple explanations of what is going on with circular polarization.

The source I recommend for anyone learning about antennas is The ARRL Antenna Book. They are currently selling the 23rd edition, but any edition from the last 30 years or so will likely suffice. Old and new versions are usually available at  local ham radio gatherings such as a “hamfest” or online at Amazon.com

The substrate of most of these boards will be made of FR4 or G10. Both of these are glass epoxy laminates. Some less popular substrates include phenolic or even aluminum.

In addition to the substrate there is copper (obviously), plus solder mask and silkscreen. The solder mask and silkscreen are often made of lacquer or epoxy-based inks. As far as I know asbestos is not used in the production of PCB’s.

It’s good that you’re concerned about personal protection, though. The glass fibers that are released when cutting these boards can still be hazardous, and personal protective equipment is always a good idea.

It’s unlikely you’ll find asbestos in circuit-board material. Most are fiberglass and epoxy. Still, you don’t want to breathe fiberglass dust when you cut a board. A dust mask and safety glasses work well to keep dust out of lungs and eyes.

Most often I use a sharp box cutter or an X-acto knife to score the PCB and then snap the sections apart. The knife doesn’t need to cut all the way through a piece of board. A small coping saw with a fine-tooth blade would also work.

Also look at jeweler’s saws that come with fine-tooth blades. You’ll need a vise or a clamp to hold the PCB steady for sawing.

I have worked with electronics for about 50 years, and with circuit board design for about 30 years. I have never even heard of a circuit board made with any asbestos. Most circuit board material is FR-4, which is glass epoxy — that is, fiberglass. It is usually 0.0625” (1/16th) inch thick.

When cutting or sanding circuit boards you should wear breathing protection — some kind of dust mask — as the dust created by cutting the fiberglass board is hazardous.

You can see more info on circuit board materials here, https://en.wikipedia.org/wiki/Printed_circuit_board.

I cannot say for all boards, but the ones I see usually specify FR4 fiberglass, which is asbestos-free. Of course, grinding fiberglass isn’t ideal either; you should always wear breathing protection while grinding ANY PCB since the dust isn’t the best thing in the world to breathe.

A "proper" PC board is made from epoxy resin with a fiberglass filler or from phenolic resin with paper filler. Any of this stuff would be better if you didn't breathe it, but it's not asbestos. One way to minimize the problem is to cut the fiberglass board with tin snips. That makes little to no dust.