Tech Forum

It is possible to use a Raspberry Pi as a Linux desktop computer, although you’ll find that it’s quite slow for many things and the selection of ready to go software is somewhat limited.

You can however install Linux on your current PC in place of Windows and the result will be a much more powerful and versatile machine that is otherwise very similar to the Raspberry Pi in function. The range of Linux distros can be overwhelming and opinions on which is best are nearly as numerous. If you are relatively new to Linux and want something that just works, I would suggest trying either Mint or Ubuntu as both strive to be beginner friendly and come configured with a look and feel that will be familiar coming from Windows.

If you are feeling a bit more adventurous then Debian is one of my own favorites. If you want to test drive Linux before you make a commitment, look for what is known as a “Live CD” which is a CD or DVD you can boot the PC from without making any changes to the existing operating system.

I attempted to use a Pi for a desktop, and it works, sort of. It was OK for web surfing but had some trouble with videos and other complex pages. Almost everything had some limitation. It worked great as a internet radio streaming device though, and that is where it lives now.

You also have to have a monitor with a HDMI or composite video (with an adapter with Pi 3) input, and by the time you buy all the pieces you need to make it work, you have spent a few bob.

Linux is the solution. Linux Mint KDE is my current favorite. If your current computer will run Win 10, it will have no problem with Linux. I have been basically Windows free for the last 10 years and it has progressively gotten better and better.  You can even dual boot it with Windows if desired to run those few pesky programs that refuse to run in Linux.

As much as I am liking my new Raspberry Pi 3, I am not ready to ditch my (Windows) computers and go all Pi. The OS seems very skinny on error handling. One ends up in the command line all too quickly. While the included LibreOffice performs OK, I feel a much better choice is Ubuntu if making the switch from Windows. Or consider a refurbished Windows 7 machine, which are plentiful. The Pi does quite fine for web browsing, but when it hiccups things get obtuse very fast.

I know some people who use Pis as their main computer. However, be aware that they are designed to run LINUX only (specifically, the “Raspberry Pi” version supplied), and they are not designed for heavy-duty use (i.e., games, audio/video processing, etc.). If all you need is a basic machine for Open Office and light web use (i.e., check e-mail), then a Pi could be what you want. Do a web search regarding Raspberry Pi accessories (there are many!) and applications to use to further see if a Pi-based machine is for you.

Why not just get an inexpensive 4 channel video surveillance box? Some can be bought without a hard disk, making them less costly.

The soft or “warm” sound of tubes relates to four properties.

1. Rolled off frequency response of the amplifier related to the inductance of the output transformers.
2. Slower transient response again due to the high inductance in the output transformers.
3. Soft clipping for very large amplitude signals due to the transfer characteristics related to the amplifier tubes.
4. Magnetic hysteresis in the transformer itself which alters the output signal of the tubes.

Transistor amplifiers have much higher slew rates, higher frequency response, and hard clipping when the large signals cause the output transistors to hit the rail voltage of the power supply.

Solid state amplifiers are directly coupled to the speaker load, have a very high damping factor due to the negative feedback, and therefore produce much more accurate output than a tube type, amp. This is the reason for the harsher sound which is really more accurate than the output from a tube amplifier.

If you compare the FFT (Fast Fourier Transform) frequency domain traces of the two types of amplifiers, the differences will become readily apparent. A solid state amp will have many more harmonic components than a tube amp. The direct coupling of the solid state amp to the speaker, also eliminates the hysteresis from the transformer core.

The lowest distortion figures will always be obtained from a solid state amp, in the less than .1% range. Tube amps, conversely are in the 1% to 5% range depending on their design.

Your looking in the wrong place: Maybe not definitive, but look here: https://en.wikipedia.org/wiki/Tube_sound. Even harmonics are more pleasant to the ear.

Yes, there are technical differences. Both tubes and transistors are nonlinear devices, and the transfer curve for each is unique. The transfer curve defines how the output should respond to the input. Within a narrowly defined range of input values, the output values change in “mostly” linear fashion — in math terms we would say the function is monotonic. When your input values start to go beyond the linear operating region the output is no longer a simple (linear or monotonic) function of the input.

Every device, triode, pentode, JFET, MOSFET, BJT has a unique transfer curve. Imagine that the transfer curve for a triode is not a straight line, but more of a “lazy-S” shape — the middle section is pretty close to straight, but the top and bottom of the curve rolls over. As mentioned above this curve “maps” your input signal to the output signal; any given value of input is a point on the curve that defines the output. But when the signal is near the very top of the curve, the output signal change for a given change of input is diminished (like a demon turning down your volume knob). This results in a soft clipping effect if the top of the transfer curve is relatively smooth. Gentle excursions into nonlinear behavior in a triode tends to produce a nice mix of even and odd harmonics; and, if I recall correctly even harmonics lend warmth to the sound.

In the case of a BJT (bipolar junction transistor), the “lazy-S” curve looks more like a “Z” drawn backwards, where the extremes of the transfer curve don’t bend gently. Instead, they have sharp “corners” and tend toward a “flatter” transfer function at the extremes. When the input signal gets into this nonlinear region a large change of input signal results in almost no change of output signal, but can produce lots of harmonics — predominantly odd-harmonics.

The clipping is more aggressive at the extremes of signal input; almost an “all or nothing” affair. Contrast that to the tube clipping, which is more like “diminishing returns.” I have heard of an amplifier circuit that adds even-harmonic components of the signal. I haven’t built it, but the idea is that it would create a warmer sound.

Having said all that, clipping and harmonic content (warm versus cool) should not be thought of as synonymous. Clipping occurs at the extreme limits of signal input. Nonlinear transfer curves can create harmonics at any value of input signal. When you look in the mirror in the morning, you are seeing a “linear” reflection of yourself. At the carnival or fairground when you stand in front of curved mirrors that distort your reflection, you are seeing an exaggerated “nonlinear” reflection of yourself. While seeing such exaggerated nonlinearity is humorous, in the audio realm it would be intolerable to listen to... maybe.

Guitar effects pedals intentionally distort the signal, sometimes to an extreme that is almost unrecognizable  — but, that’s an article for another day.

The answer is simple, really. Tubes don’t so much clip, as go soft, rounding the peaks off the waveform. Solid state, however, works all the way up until it hits the head; at which point it cuts it off sharply. The resulting distortion can be either modeled as odd harmonics for solid state, or even harmonics for tube amps. And it’s all in how they are perceived by the ear; the softer clipping that tube amps do causes it to be more perceived as being not quite as loud, whereas the hard clip of solid state tends to be rougher sounding. And to conclude - if your system routinely clips, you need to Tim Allen (MORE POWER!) it.

In this case, all clipping isn't the same. A transistor circuit is fine up to the power supply voltage, where it mows the peaks off square and flat. This produces a harsh distortion similar to the fuzz pedal for a guitar. A tube circuit starts to round off the peaks before they actually run into the power supply voltage. The rounder peaks account for the "warmer" sound.

It's not about clipping. Tubes and FETs have greater inherent 2nd harmonic distortion which gives them the warm sound. Look up the books and articles by Douglas Self to truly understand why modern bipolar output amplifiers are very hard to beat for sonic clarity. Some of the new Class D amplifiers (TI, others) are quite amazingly clear, too. I still use FET input op amps (LF412) when I want some of that tube warmth. But when I need absolute clarity, modern bipolar devices (LM833 and newer) for crossovers, and bipolar output stages, are (in my opinion) best. Read what Self has to say.

It has to do with the type of distortion between the two architectures. Tubes tend to have more odd-order harmonic (3rd, 5th, etc.) distortion; solid-state amps are relatively distortion-free, and any distortion they have is generally with even-order harmonic (2nd, 4th, etc.) distortion usually generated by their feedback circuitry. With clever signal filtering schemes, solid-state amps can mimic the warmth, etc. of tube amplifiers, without the power-wasting (i.e., heat) that tube amps have.

Simple answer: To the first order, they are pretty similar, however, typically tube circuits are operating at a much higher voltage — a transistor circuit operating at lower voltage, will tend to have higher harmonic distortion than a tube operating at a higher voltage. If you use a high voltage transistor then you can get harmonic distortion from a transistor which is comparable to (or better than) a tube, but you usually have a higher noise floor.

After a couple trips across town to jump start my wife’s car, I installed a relay to automatically turn the lights off when the ignition was turned off. All you need is one of the generic automotive 30A relays. If you can find the power wire to the headlamp switch, cut it in a convenient place and place the contacts of the relay in series with the headlamp switch. Then connect the relay coil between a switched 12V source (turns on/off with ignition) and ground. The lights will only work when the ignition is on.

If the power wire for the headlamp switch is inaccessible, then remove the headlight fuse, get a relay and an inline fuse of the same value as your headlamp fuse. Then connect the fuse to the hot side of your original fuse holder, the other side of the fuse to one of the relay contacts (usually 30) and the other relay contact (87) to the other side of your original fuse holder. The coil connections will be as above.

Auto-headlights is moderately difficult because of the length of the delays and the quiesient current. Probably best done with a microcontroller; Light level sensing is generally time based and then it stays on until the ignition is turned off. I don’t know what the times are. But take going under a bridge a mile long or so. I think it takes about 20 seconds for the lights to turn on, Never paid attention to the off threshold/time.

I can, however, offer you a simple design that I used in 1982 on my vehicle. In that particular vehicle, there was +12 available when the tail lights were on and ground via the driver’s door switch, when the driver’s door was opened. There was already an isolation diode there anyway, so I took advantage of it. I had an EASY way of “buzzer on if lights were on and driver’s door was open.” So (to +12 when parking lights on), a piezo buzzer and a diode to the driver’s door switch (ground when open, +12 when closed). I had to replace the buzzer a few times in 17 years. The high temperature kills them.

Now, one car has 1. Lights stay on until the driver’s door is opened (actually radio too) 2. A few different delays are possible for how long the lights stay on.

The other has 1. Lights turn off when the door is opened and car is off. Both have auto-on by daylight sense. In both of these cases, in order to turn-off the lights when the engine is on, you have to do something heroic.
Car #2 Turn-off car and open the door. Turn off the headlights. if they are on.

Car #1 Stop. Turn off car, engage parking brake. Turn on car which will turn off lights. If you want to start the engine with the lights off, the parking brake must be set. Turning them off is not so easy. Blinking the high beams is easy on car #2 (momentary and full on stalk switch). In car #1 it’s not possible. For auto-on; timed off, there are a lot of issues to deal with. Turning the lights off briefly is very useful if you confront a deer.

You just need a 12 volt, single pole single throw relay. Wire the contacts in series with the headlight power wire and power the relay from the ignition switch accessory terminal. You may have to find it by trial and error among the wires coming out of the steering column, or a auto repair manual may tell you the color of the wire.

Typically, the easiest way to do this is to connect a diode, a suitable resistor and a sonalert from the headlight switched positive to the RUN position of the ignition switch. If the headlights are left on when the ignition switch is turned off, the sonalert will sound. The diode prevents the sonalert from sounding when the car is running and the headlights are off. The resistor scales the 12VDC to a lower voltage for the sonalert if necessary. This is much simpler then an automatic switch, and it consumes no power.

I have to ask myself why anyone would put a GFI on the garage door opening circuit/electronics? I see no need for such a thing.

The reason we have GFI protected outlets is because someone could unintentionally become a ground path for the AC current. This could be deadly.

With a garage door circuit, no one should be playing with the circuit unless the electricity to the unit is off. It is a servicing issue NOT a use issue.

In other words, if the circuit is being used as intended, then there is no way you will inadvertently become a grounding path for the circuit. The circuit is protected in a housing and not available, as is an AC outlet, for you to come in contact with.

Disclaimer: This is an opinion of the sender only, not advice as to what you should do.

You can buy them. You can make them. What is the normal trip level, you’d have to look up. A resistor (suggest metal oxide) from ground to hot, at about 6 mA should trip the GFCI. e.g. R<=120/0.006 The problem is more complex when you look here: www.csemag.com/single-article/ul-s-new-gfci-classes/89c8746cdc4a7fd8a3cb93f1d51ba57a.html I actually suspect that you may have an AFCI/GFCI combination and it’s tripping on an arc fault because of the motor. If that’s the case, I would consider an RFI filter (possibly medical grade which has a lower leakage) and appropriately sized ZNR’s. There have been reports of just plain flakey GFCI’s. So contact the manufacturer too.

Working with live power lines can be dangerous. I purchased a GFCI tester from Home Depot similar to this one: www.homedepot.com/p/Gardner-Bender-120-VAC-GFCI-Outlet-Tester-Case-of-5-GFI-3501/202867890. To verify that the GFCI outlet can deliver higher currents, plug in a hair dryer or room heater. Make sure you don't overload your circuit. The trip level for a UL 943 Class A GFCI is 4 to 6 mA, or about 24K ohms from hot to safety. I don't recommend building your own circuit. Buy a device that is already built for this purpose.

As indicated in http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html , a GFI is supposed to trip if there is 5 mA of difference in current flow between the hot and neutral (return) wires in the protected circuit. The "test" button puts a resistor between the hot and ground wires. You could put a larger value resistor between the hot and ground to see if the GFI does not trip with some smaller current. A 56K resistor, for instance would provide about 2.1 mA. If that trips the GFI, then the GFI may be too sensitive. It is more likely that there is an intermittent short to ground in the door opener, or that the door opener is too close to the current limit of the GFI (which also acts as a circuit breaker, usually 15 or 20A).

Your best bet is to replace the breaker — don’t waste the time, etc. trying to “test”it.

Many hardware or big box stores carry testers for receptacle testing, they have three lights to indicate correct wiring. Some of these have a test button to check operation of the of GFI devices.