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The Open Book Project: An eBook Reader You Can Build Yourself
2 Feb 2020 6:00am, by David Cassel
An amateur hardware enthusiast wants to prove it’s possible for people to build their own ebook readers.
“As a society, we need an open source device for reading,” explains the project’s page on GitHub. “Books are among the most important documents of our culture, yet the most popular and widespread devices we have for reading — the Kobo, the Nook, the Kindle and even the iPad — are closed devices, operating as small moving parts in a set of giant closed platforms whose owners’ interests are not always aligned with readers’.”
“The Open Book aims to be a simple device that anyone with a soldering iron can build for themselves.”
Q:
I went through following app note, where OPA333 is used in 400V bus current sensing application, also i have seen current sensor which have term called common mode voltage, which is specify the max voltage that can be applied to sensor inputs (current amplifier).
OPA333 does not mentions anything like that,
I don't understand how OPA333 withstand 400V on its input terminals without burning up?
A:
The OPA333 isn't referenced to ground. It is referenced to the 400V supply bus via the zener diode and Rz. Well, technically the OPA333 is using 400V-5.1V as it's reference, but that reference is always relative to the 400V rail.
Instead of the OPA333 being powered by a potential difference that "sits above" GND by 5.1V, it is a voltage that "hangs below" the 400V bus by 5.1V.
Since the current sense resistor is on the high side and only has a tiny voltage drop across it, it is well within the OPA333's power supply which is 400V for the positive and 400V-5.1V for the negative supply terminals
Therefore, the OPA333's output is basically ~400V above GND and so needs to be re-referenced (shifted) to GND so that the other circuitry (which is GND referenced) can read it. This is done with the P-FET which is rated for 600V since it does have a huge voltage drop across it.
The most interesting part of this circuit is actually the level shifter. I understand why the current through both resistors has to be the same but I don't understand how the negative feedback is able to turn on the PMOS by just the right amount to drop all the excess voltage from the 400V rail.
EDIT: I sort of see how the feedback works now but it's pretty subtle. All the negative feedback does is turn on the PMOS just enough so that the two OPA333 inputs equal each other. This causes the voltage across R1 to match the voltage drop across Rshunt. That's the most direct thing the negative feedback does and the only thing the op-amp is really doing/controlling. Everything else: the current mirroring, the level shifting, and dropping the excess voltage is a byproduct.
The currents through R1 and R2 must be equal, and since their resistances are equal then their voltage drops must also be equal. This achieves the voltage mirroring and level shift. Therefore all the remaining voltage must be dropped across PMOS. It has no choice. It's the most important function of the circuit but is also the most indirect result of the whole operation.
Like a fancy version of how a resistor drops all the excess voltage so the LED doesn't have to. It just has no choice because the LED voltage drop already has its voltage drops defined and fixed.
The Zener Diode Regulator
Zener Diodes can be used to produce a stabilised voltage output with low ripple under varying load current conditions. By passing a small current through the diode from a voltage source, via a suitable current limiting resistor (RS), the zener diode will conduct sufficient current to maintain a voltage drop of Vout.
We remember from the previous tutorials that the DC output voltage from the half or full-wave rectifiers contains ripple superimposed onto the DC voltage and that as the load value changes so to does the average output voltage. By connecting a simple zener stabiliser circuit as shown below across the output of the rectifier, a more stable output voltage can be produced.
Just a few decades ago, getting into hobby radio meant lots of specialty hardware, and making changes to your setup to work on various frequencies wasn’t particularly easy. Since software-def…
In contrast to Asmyldof's answer I would be inclined to make a dual-mode input as is common on industrial PLCs, etc. Typically these add a 500 Ω shunt resistor across the 0 - 10 V input to convert 20 mA to 10 V.
I've been playing with more 4-20mA stuff. I want to design my input section to be fairly "bullet proof", since the sensor I am using - I have no idea if it could fail and dump the full 24V supply through the item and into my receiver's front end.
Referencing the little diagram below, my receiver has a 200 ohm 1% resistor. I've rated it for 3 watts since 24v into 200 ohms yields 120mA, or 2.88 watts, so that item is safe enough even at full loop voltage.
Now, if you focus your eye at dead centre of the picture you will see that the voltage is always zero volts. This is because a dipole is optimally driven with a balanced voltage source (VOVO). A balanced voltage source is preferred for a dipole antenna. In fact, the voltage and electric field is zero all along the length of the green line below: -
This means you can optionally regard that green line as earth (providing the antenna is driven in a balanced way). Now if you were to cut the above picture in half you'd have a 1/4 λλ monopole driven with an unbalanced voltage source. An unbalanced voltage source is one that has typically 0 volts on one leg while the other leg does the voltage driving: -
And, not surprisingly, it has one half of the impedance presented by the half wave dipole. But, to keep the same radiation pattern you need to "force" an earth plane that does what the green line does.
Schematic for THAT Thing, a do-it-yourself preamp/electronics project by Curt Yengst, featured in the Jan. 8, 2020 issue of Radio World.
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- Hard Silver Ag[97-98%], Cu+Ni
General application relays. The copper and nickel contents give hardness. Long contact life, but tends to oxidise at higher temperatures.
- Silver Nickel AgNi
A good standard contact material. More resistant to welding at high loads than hard silver. High burnout resistance.
- Silver Cadmium Oxide AgCdO
More resistant to welding at high switching current "peaks" so is used for high AC loads. Not recommended for strong DC breaking arcs because of the wear this creates.
- Silver Tin Oxide AgSnO2
Material is more resistant to welding at high making current peaks due to the tin oxide. Has a very high burn out resistance when switching high loads. Low degree of material migration under DC loads. Useful where very high inrush currents occur. Silver Tin Oxide is frequently chosen as the replacement relay contact material for Silver Cadmium Oxide which is more harmful.
- Silver Tin Indium AgSnOinO
Similar to Silver Tin Oxide but more resistant to inrush.
- Tungsten W
More resistant to welding at high loads than hard silver, with high burnout resistance.
- Gold Plating 10µm Au
Used for switching low loads > 1mA/100mV. The plating will be removed by friction and erosion after around 1 million switching cycles in "dry circuits".
- Gold Plating / Flash 3µm Au
Same qualities as 10µm Au but is less durable. It is generally used to prevent corrosion / oxidation of relay contacts during storage.
Good software, not really… Usable software, yes. RF Analyzer and SDRtouch are two decent spectrum analyzers for Android. Both support the RTL-SDR and HackRF. There is also Avare ADSB for the RTL-SDR on Android.
Here we have the “RTL-SDR Blog v3” receiver, which is one of the most popular “next generation” RTL-SDR receivers. The plastic case has been replaced with an aluminum one that not only reduces interference, but helps the board dissipate heat while in operation. The crystal has been upgraded to a temperature compensated oscillator (TCXO) which helps reduce temperature drift. The R820T2 tuner is paired with a standard SMA antenna connector, and both it and the RTL2832U have some unused pins broken out if you’re looking to get into developing modifications or expansions to the core hardware. //
In the years since its inception, the RTL-SDR project has become the de facto “first step” for anyone looking to experiment with radio. It’s cheap, it’s easy, and since the hardware is incapable of transmission, you don’t have to worry about accidentally running afoul of the FCC or your local equivalent. Honestly, it’s difficult to think of a valid reason not to add one of these little USB receivers to your bag of tricks; even if you only use it once, it will more than pay for itself.
Before the arrival of reliable, easy-to-use LED displays like the Monsanto MAN-1, companies came up with a vast array of impractical methods to display numbers and characters. Projection displays, such as the one shown here, are one of these fringe display types, and were designed to compete directly with the neon filled Nixie tubes that were the leading display of the time. Also known as a "One Plane Readout" or "In Line Display", these devices were invented by IEE in 1956 for use in their proprietary industrial control systems; the devices proved so popular with customers that IEE began producing and selling the displays as a stand-alone product.
A projection display functions like a miniature slide projector, only the "slides" are numbers, each with its own separate lamp for electrical control. In this IEE display, light from one of 12 different lamps is projected through one of 12 focusing lenses, which directs the light beam onto the appropriate number mask. Light exiting the digit mask passes through a second set of lenses, which bends the light to project the image of the digit mask onto the center of a fogged plastic screen at the front of the display.
Projection displays are complex devices with numerous parts, and were expensive to manufacture compared to a Nixie tube.
You can build a "poor man's" pyranometer that works pretty well out of inexpensive and readily available components. Although it will not be of laboratory quality, it will suffice for comparative measurements and educational purposes.
Making the Meter
The obvious component to consider as the basis for our meter is a silicon photovoltaic cell. When sunlight strikes it, it produces electricity, and the more sunlight strikes it, the more electricity it produces.
At first glance, you might think that you could just hook a voltmeter up to it and measure the output voltage. Unfortunately, if you do this, you will get very erroneous results (visit the Appendix if you want to understand why).
Instead, you will need to measure the cell's output current. If you short out (hook a perfect wire between) the positive and negative terminals of your cell, a current flows through that wire. That is the current that you would like to measure. It varies linearly with the amount of sunlight striking the surface of the cell. This is actually a little trickier than one might think, for reasons that are explained in the Appendix.
TinyCAD - the free circuit design program
TinyCAD is a an open source program for drawing circuit diagrams which runs under Windows.
This site is for sharing circuit design symbols for TinyCAD.
Creating libraries of circuit symbols in TinyCAD is easy, but time-consuming. If you have some symbols you feel might benefit other TinyCAD users, then why not upload the symbols to this site to allow other users to download them?