# Tag Info

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### Ceramic caps vs electrolytic. What are the tangible differences in use?

1. Capacitors There are a lot of misconceptions about capacitors, so I wanted to briefly clarify what capacitance is and what capacitors do. Capacitance measures how much energy will be stored in the ...

### Ceramic caps vs electrolytic. What are the tangible differences in use?

For example, why do I see it suggested to use ceramic caps for power decoupling per microprocessor & a larger electrolytic capacitor per board? why not use electrolytic all around? The three ...
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### Why do microcontrollers have so little RAM?

There are several reasons for this. First of all, memory takes up a lot of silicon area. This means that increasing the amount of RAM directly increases the silicon area of the chip and hence the ...
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### Why do LEDs have a maximum current?

It's difficult to come up with an analogy because the usual analogies for electrical systems are fluid systems. A great thing about fluid systems is that the working fluid is also good at cooling ...
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### Is Gaussian noise equal to white noise?

No, they are completely orthogonal concepts. The probability distribution says nothing about the frequency content, and the power distribution across frequency says nothing about the sample ...

### Ceramic caps vs electrolytic. What are the tangible differences in use?

The obvious difference is that electrolytics are much bigger than ceramics. 1mm by 0.5mm ceramics are common garden variety, your electrolytic cans are far larger. Then, as others have pointed out ...

### Will the net current drawn by a microcontroller equal the current supplied by it

Will the net current drawn by a microcontroller equal the current supplied by it No, because the microcontroller itself (its clocks, IO control drivers, its CPU) need current, too. where can I find ...
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### Why isn't a transformer a short circuit?

As transformers are usually used with AC rather than with DC, there is what is known as inductance $L$, which is a property of a conductor to "resist" the changes in the current flowing in it due to ...
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### How do I really calculate these resistors?

You've done the calculations correctly, but the entire basis for the calculations is just a rough approximation of transistor behavior. As you see, $V_{BE}$ isn't really exactly 0.7V (most of the ...
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### Why are circuit results different from theorised?

Your measurements are impossible if the circuit shown is correct. 12V / 20kΩ = 0.6mA. Therefore there cannot be 8.03mA going into the Base. However the slightly high Base-Emitter voltage ...

### Why do LEDs have a maximum current?

There's a forward voltage drop of a couple volts across the LED. This Voltage drop times the Current is the Power dissipated in the device. It creates light, but also heat. It's the heat that kills ...

### Is there a formula to determine the size of decoupling capacitors?

Remember decoupling has several purposes. On a load which draws transient, spiky currents like a CPU, decoupling caps store energy locally and close to the load, so it is available quickly (ie, with ...

### Why do microcontrollers have so little RAM?

Memory probably takes up the most silicon space, and RAM being very fast to use is volatile - and uses power constantly to keep its state. Unless you need lots of RAM, it's not useful for many other ...
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### Caculating baud rate of Ethernet per wire

A 100BASE-TX device transmits on 1 pair (2 wires) and receives on another pair (2 more wires). Because of the 4B5B encoding -- for each 4 data bits, it transmits a series of 5 symbols -- 100BASE-TX ...

### Magnet that needs power to turn off? Inverse coil?

It's possible to "turn a magnet off" without requiring continuous power in either position- simply shunt the field lines away from the open end. Here is an example of a magnet with an on-off switch: ...

### Why do microcontrollers have so little RAM?

Besides the excellent points brought up in the other answers, another reason for limited RAM is the architecture of the microcontroller. For example, take the the Microchip PIC10LF320, which has only ...
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### Is there any relationship between frequency of signal and distance it travels?

In general, yes, higher frequencies attenuate more the further distance they travel. There are two effects that are responsible for this. First, higher frequency radio waves tend to be absorbed more ...

### Noise and what does V/√Hz actually mean?

Is this value useful in calculating signal to noise ratio? Or what fun calculations can I do with this number? To convert the spectral density $\tilde v$ (in nV/√Hz) to a voltage (in VRMS), you ...
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### Theory question about "j" imaginary unit (AC circuit analysis)

If you put a minus sign in front of the number "5" it becomes "-5". Try and look at this differently. Try thinking that it rotates the number "5" (tied to the origin by a piece of string of length 5)...

### Why do LEDs have a maximum current?

TL;DR: Flowing current creates heat, and for LEDs, heat kills the part. Whenever electrons flow through a conductor, Joule heating happens. This is partly because of what heat really is, particles ...
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### How serial resistors actually reduce EMI?

Well one it slows down the rise time of your signal which reduces the high frequency content. So that could help you if you didn't need your edges to be that fast. It also lowers the current flowing ...

### How do I really calculate these resistors?

You have done the calculations correctly. However, your biassing scheme will only work well with one set of transistor parameters, it's very sensitive to variations in beta. A better biassing scheme ...
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### Estimate capacitor parameters

Capacitance is given by: This is the formula applicable for free space or vacuum. If you are using a dielectric material between the plates, you multiply the resultant capacitance with the relative ...
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### Why is power of a signal equal to square of that signal?

If the signal is represented as a voltage $v(t)$ or a current $i(t)$ and it is connected to a (1 ohm) resistor, the power dissipated in the resistor is proportional to $v^2(t)$ or $i^2(t)$. ...
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### Will the net current drawn by a microcontroller equal the current supplied by it

Here's a diagram of a microcontroller IC, with four outputs. The top two outputs OUT1 and OUT2 are sinking current from Vcc (via R1 and R2), and the bottom two outputs OUT3 and OUT4 are sourcing ...
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### About power dissipation of capacitors and inductors & I-V phase difference

If the voltage across a capacitor is described as sin(x), then the current through the capacitor (being 90 degrees out of phase) can be described as cos(x). The power is given by the product of ...

### Theory question about "j" imaginary unit (AC circuit analysis)

In pure maths we use $i$ to represent the prime square root of $-1$. The other square root of $-1$ being $-i$. If you imagine a number line with real numbers placed horizontally. We ...
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### Why pulsed DC passes through a capacitor?

Zero volts doesn't mean zero current. Assume your circuit looks like this: simulate this circuit – Schematic created using CircuitLab When the switch turns on (connects to 10V), current flows ...