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We love our props here at Hackaday, and whenever we come across a piece from the Back To The Future fandom, it’s hard to resist showcasing it. In this case, [Xyster101] is showing of his build of Doc Brown’s Flux Capacitor.

[Xyster101] opted for a plywood case — much more economical than the $125 it would have cost him for a proper electrical box. Inside, there’s some clever workarounds to make this look as close as possible to the original. Acrylic rods and spheres were shaped and glued together to replicate the trinity of glass tubes, 3/4″ plywood cut by a hole saw mimicked the solenoids, steel rods were sanded down for the trio of points in the centre of the device and the spark plug wires and banana connectors aren’t functional, but complete the look. Including paint, soldering and copious use of hot glue to hold everything in place, the build phase took about thirty hours.

The LEDs have multiple modes, controlled by DIP switches hidden under a pipe on the side of the box. There’s also motion sensor on the bottom of the case that triggers the LEDs to flicker when you walk by. And, if you want to take your time-travel to-go, there’s a nine volt plug to let you show it off wherever — or whenever — you’re traveling to. Check out the build video after the break.

With this flux capacitor in hand, grab this time circuit display and cram them both into eD, the electric DeLorean, and you’re well on your way to living in the future.

[Via Imgur]


Filed under: Arduino Hacks

We love our props here at Hackaday, and whenever we come across a piece from the Back To The Future fandom, it’s hard to resist showcasing it. In this case, [Xyster101] is showing of his build of Doc Brown’s Flux Capacitor.

[Xyster101] opted for a plywood case — much more economical than the $125 it would have cost him for a proper electrical box. Inside, there’s some clever workarounds to make this look as close as possible to the original. Acrylic rods and spheres were shaped and glued together to replicate the trinity of glass tubes, 3/4″ plywood cut by a hole saw mimicked the solenoids, steel rods were sanded down for the trio of points in the centre of the device and the spark plug wires and banana connectors aren’t functional, but complete the look. Including paint, soldering and copious use of hot glue to hold everything in place, the build phase took about thirty hours.

The LEDs have multiple modes, controlled by DIP switches hidden under a pipe on the side of the box. There’s also motion sensor on the bottom of the case that triggers the LEDs to flicker when you walk by. And, if you want to take your time-travel to-go, there’s a nine volt plug to let you show it off wherever — or whenever — you’re traveling to. Check out the build video after the break.

With this flux capacitor in hand, grab this time circuit display and cram them both into eD, the electric DeLorean, and you’re well on your way to living in the future.

[Via Imgur]


Filed under: Arduino Hacks
Lug
13

Measure Capacitance with Arduino

arduino, capacitor Commenti disabilitati su Measure Capacitance with Arduino 

FXGPAOHIBWHE68V.MEDIUM

by Maximous @ instructables.com:

This tutorial provides a guide on how to set up an Arduino to measure the capacitance of a capacitor. This can be useful if the capacitor is unlabeled or if it is self-built.

Capacitance is an object’s ability to store an electric charge. Reasonably, this object is referred to as a capacitor. A capacitor that stores this charge in an electric field between two conductive plates is known as a parallel plate capacitor.

Measure Capacitance with Arduino – [Link]

Dic
17

Arduino-based inductance meter

arduino, capacitor, inductance, LCR, resistor, Test/Measurements Commenti disabilitati su Arduino-based inductance meter 

mg_1131-600

Lukas of Soldernerd built a DIY Arduino-based inductance meter:

I’ve just finished a little Arduino project. It’s a shield for the Arduino Uno that lets you measure inductance. This is a functionality that I found missing in just about any digital multi meter. Yes, there are specialized LCR meters that let you measure inductance but they typically won’t measure voltages or currents. So I had to build my inductance meter myself.

[via]

Arduino-based inductance meter - [Link]

Set
25

Safety warning: Arduino GSM shield may cause fires

arduino, Arduino GSM, arduino hacks, BaldEngineer, capacitor, gsm, Manganese Dioxide, News, Tantalum capacitor Commenti disabilitati su Safety warning: Arduino GSM shield may cause fires 

arduGSMfire

Be careful with those Arduino GSM cards. As [James] reports, they may turn into fire starters. One person has reported a small explosion and fire already on the Arduino forums.
Now before we go any further – You may be asking yourself who the heck [James] is, and what gives him the ability to second guess the Arduino team. Well, here is [James'] blog disclaimer:  “James is a Senior Technical Expert for Technology and Applications at KEMET Electronics, a capacitor manufacturer. The content of this post are his and in no way reflects opinions of his employer.”

Senior Technical Expert?  That’s a good enough reason for us to believe him.

[James] states the problem is a tantalum capacitor used to decouple the GSM radio power supply from the main Arduino supply.
Tantalum capacitors are great for their low ESR properties. However, they have a well known downside of getting very hot, or even exploding when stressed. It’s not the Tantalum Anode that is burning. The Manganese Dioxide used as a cathode in some Tantalum capacitors is the culprit.

It comes down to voltage rating (or more aptly, derating). The Arduino GSM shield runs at 5 volts. The designers chose a 6.3V rated capacitor. While this close of a tolerance may be good enough for some types of capacitor, it is a no-go for a Tantalum cap with Manganese Dioxide. The dielectric material in these capacitors is so thin that the stress of a reflow oven cycle causes cracks. The cracks pass leakage current, and this sets the Manganese Dioxide on the path to destruction.
What’s the solution? [James] suggests several options:

  1. Switch to a 10 volt part
  2. Switch to a safer Tantalum Polymer capacitor.

We haven’t heard anything from the Arduino team yet about this, but to be safe we’d follow [James'] advice.


Filed under: Arduino Hacks, news

Hello readers

Today we continue down the path of analog electronics theory by stopping by for an introductory look at the RC circuit. That’s R for resistor, and C for capacitor. As we know from previous articles, resistors can resist or limit the flow of current in a circuit, and a capacitor stores electric current for use in the future. And – when used together – these two simple components can be used for many interesting applications such as timing and creating oscillators of various frequencies.

How is this so? Please consider the following simple circuit:

When the switch is in position A, current flows through R1 and into the capacitor C1 until it is fully charged. During this charging process, the voltage across the capacitor will change, starting from zero until fully charged, at which point the voltage will be the same as if the capacitor had been replaced by a break in the circuit – in this case 6V. Fair enough. But how long will the capacitor take to reach this state? Well the time taken is a function of several things – including the value of the resistor (R1) as it limits the flow of current; and the size of the capacitor – which determines how much charge can be stored.

If we know these two values, we can calculate the time constant of the circuit. The time constant is denoted by the character zeta (lower-case Greek Z).

The time constant is the time taken (in seconds) by the capacitor C that is fed from a resistor R to charge to a certain level. The capacitor will charge to 63% of the final voltage in one time constant, 85% in two time constants, and 100% in five time constants. If you graphed the % charge against time constant, the result is exponential. That is:

Now enough theory – let’s put this RC circuit to practice to see the voltage change across the capacitor as it charges. The resistor R1 will be 20k ohm, the capacitor 1000 uF.

Our time constant will be R x C which will be 20000 ohms x 0.001 farads, which equals 20 (seconds).  Notice the unit conversion – you need to go back to ohms and farads not micro-, pico- or nanofarads. So our example will take 20 seconds to reach 63% of final voltage, and 100 seconds to reach almost full voltage. This is assuming the values of the resistor and capacitor are accurate. The capacitor will have to be taken on face value as I can’t measure it with my equipment, and don’t have the data sheet to know the tolerance. The resistor measured at 19.84 k ohms, and the battery measured 6.27 volts. Therefore our real time constant should be around 19.84 seconds, give or take.

First of all, here is a shot of the little oscilloscope measuring the change in voltage over the capacitor with respect to time. The vertical scale is 1v/division:

And here is the multimeter measuring the voltage next to a stopwatch. (crude yet effective, no?)

The two videos were not the most accurate, as it was difficult to synchronise the stopwatch and start the circuit, but I hope you could see the exponential relationship between time and voltage.

What about discharging? Using the circuit above, if we moved the switch to B after charging the capacitor –  and R2 was also 20k ohm – how long would it take to discharge the capacitor? Exactly the same as charging it! So one time constant to discharge 63% and so on. So you can take the graph from above and invert it as such:

How can we make use of an RC circuit?

I’m glad you asked. Consider the following circuit:

When power is applied, the capacitor starts to charge, and in doing so allows current to flow to the emitter of the transistor, which turns on the LED. However as the capacitor charges, less current passes to the base of the transistor, eventually turning it off. Therefore you can calculate time constants and experiment to create an off timer. However, a preferable way would be to make use of a 555 timer. For example, an RC combination is used to set the pulse length used in astable timing applications, for example using R1, R2 and C1:

(For more information on the 555 timer, please read this article)

Another use of the RC circuit is oscillating. Due to varying capacitor values due to tolerance, you most likely cannot make precision frequency generators, but you can still have some fun and make useful things. Here is a classic oscillator example – an astable multivibrator:

What is going on here? Here it is in action:

and here is one side being measured on the little scope:

We have two RC circuits, each controlling a transistor. When power is applied, there is no way to determine which side will start first, as this depends on the latent charge in the capacitors and the exact values of the resistors and capacitors. So to start let’s assume the left transistor (Q1) and LED are on; and the right transistor (Q2) and LED are off. The voltage at collector of Q1 will be close to zero as it is on. And the voltage at the base of Q2 will also be close to zero as C2 will initially be discharged. But C2 will now start charging via R4 and base of Q1 to around 5.4V (remember the 0.6v loss over the base-emitter junction of a transistor). While this is happening, C1 starts charging through R2. Once the voltage difference reaches 0.6V over the capacitor, Q2 is turned on.

But when Q2 is on, the voltage at the collector drops to zero, and C2 is charged, so it pulls the voltage at the base of Q1 to -5.4v, turning it off and the left LED. C1 starts charging via R1, and C2 starts charging via R3 until it reaches 0.6v. Then Q1 turns on, bringing the base of Q2 down to -5.4V – switching it off. And the whole process repeats itself. Argh. Now you can see why Arduino is so popular.

Time for a laugh – here is the result of too much current through a trimpot:

So there you have it – the RC circuit. Part of the magic of analogue electronics!

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our new Google Group.

Otherwise, have fun, be good to each other – and make something! :)


Giu
03

Electronic components – the Capacitor

capacitor, ceramic, education, electrolytic, learning electronics, polyester, tronixstuff Commenti disabilitati su Electronic components – the Capacitor 

Hello readers

Today we continue with the series of articles on basic electronics with this introductory article about the capacitor.

What is a capacitor? A very simple answer to that question is a part that stores electric current for use in the future. How is this so? A capacitor is made up of two conductive plates, separated by a dielectric. The plates can be made from conductive material such as aluminium, and the dielectric is between these conductive plates. Dielectrics can be made from nothing (i.e. be a tiny gap between the plates or a vacuum), paper, plastic film, glass, a special kind of fluid, or ceramic material.

When a difference in potential exists across the plates (a change in voltage) an electric field is created between the plates, which stores electrical energy – charging the capacitor. When the potential difference is removed, the energy will leak through the dielectric until the potential no longer exists – in other words discharging the capacitor. The amount of energy that a capacitor can hold – its capacitance, is a unit of measure called the Farad.

The term farad is named after an Englishman by the name of Michael Faraday, a genius chemist and physicist that discovered (amongst many other things) the concept of electromagnetic fields. Anyhow, one farad (F) is quite a lot of energy, so capacitors usually store much less. The most common units of measurement are the following:

  • picofarads – pF – 10^-12 – 0.000 000 000 001 F
  • nanofarads – nF – 10^-9 – 0.000 000 001 F
  • microfarads – uF – 10^-6 – 0.000 001 F

As well as the capacitance value, the other common parameters of a capacitor are:

  • the voltage (never exceed your voltage!)
  • leakage current – capacitors are not perfect and do leak a very tiny amount of current, usually in the micro-ampere range
  • tolerance – similar to resistors, actual versus manufactured values can vary – sometimes up to 20% either way
  • working temperature – always check this if your project involves extreme temperatures

It is always interesting to read component data sheets, and this is no exception for capacitors. You can learn a lot about the individual parameters and design your project accordingly. Here is a typical example of a data sheet for an electrolytic capacitor from Vishay. And here are the schematic symbols for non-polarised and then polarised capacitors:


At this point let’s have a look at the various types of popular capacitors:

Electrolytic Capacitors


These are used when very high values of capacitance are required, for power smoothing, spike suppression and so on. They consist of two sheets of aluminium foil, one sheet covered with an oxide coating, separated by paper soaked in electrolye – this is rolled up and inserted into a cylinder, with two wires inserted. As the electrolyte is a liquid, it is affected by ambient temperature. Therefore as temperature increases, the capacitance increases – and vice versa. Therefore temperature extremes need to be taken into account, and perhaps other types of capacitors used. The capacitors in the photo above are radial capacitors; you can also find axial capacitors with one lead at each end. Note that electrolytics are polarised! They have a positive and negative lead – the negative is normally indicated by the striped-arrow line (see above).

V-chip capacitors

These are surface-mount electrolytic capacitors, for example these two on my Arduino Duemilanove (below).

Ceramic capacitors

These are very small, constructed from layers of aluminium and ceramic material.

Their capacitance is also very low, the lowest I have seen is 0.015 picofarads. Typically used in situations that have high frequencies, such as spike protection for integrated circuits. Reading the value is quite simple, the first two digits are the significant figures, and the third is the multiplier. The result is always picofarads. For example. 121 is 120 picofarads, 8.2 is 8.2 picofarads, 12 is 12 picofarads. If there is a letter suffix, this indicates the tolerance:

  • C = +/1 0.25pF
  • D = +/- 0.5 pF
  • J = 5%
  • K = 10%
  • M = 20%
  • P = +100%/-0%
  • Y = -20%/+50%
  • Z = -20%/+80%

If there are numbers after the tolerance, they normally state the maximum working voltage. If your capacitor does not have a tolerance printed on it, assume it is between 10 and 20%. Or better yet, replace it with a better capacitor that states the tolerance.

Polyester capacitors


These are also very popular for high-frequency circuits, as they can discharge very quickly and have a very low leakage. The older styles (green/brown above) – read their values is the same as the ceramic capacitors (above), with a slight difference – sometimes (!) the voltage rating is before/above/below the value code. So using the green example above which reads “2A683J”, this breaks down to the voltage rating 2A, and the value 683, then the tolerance J. Voltage ratings are:

  • 2A – 100V DC
  • 2E – 250V DC
  • 2G – 400 V DC
  • 2J = 630V DC

So the 2A683J will have a voltage rating of 100V, a tolerance of 5%, and a capacitance of 68000 picofarads (0.068 uF or 68 nF).

Please note – this coding does seem to vary by manufacturer. Some will actually have (e.g.) 630V printed on them, and some even have their own coding. If you are unsure of the voltage rating, one has to really examine the circuit the capacitor is located in, or hunt down the data sheet. When buying new parts, it pays to get the data sheet from the distributor, then file it away indexed with your stock control database.

The newer styles (blue above) are different again. This one is 0.47 uF 63 volts 10% tolerance.

Variable capacitors


There are two main types – trimmer capacitors (above right) used for fine-tuning; and normal variable (or mini-tuning) capacitors (above left) used for applications such as radio tuning. Usually have a set range, for example the tuning capacitor’s range is 60 to 160 picofarads. The schematic symbol for trimmer capacitors is:

and for variable capacitors is:

Tantalum capacitors

Can be used as a replacement for electrolytic capacitors where space is at a premium, and a more accurate and less leaky (electrically that is) solution is required. Tantalums are also polarised (see the tiny ‘+’ in the photo above).

Surface-mount capacitors

There are many types of capacitor in surface-mount packaging. Hover over the images below for descriptions:

Mathematics of capacitors

Working with capacitors is easy, however some mathematics may be required. If you recall the formulae associated with resistors, you will find this quite easy.

Capacitors in parallel

This is simple – the total capacitance of parallel capacitors is the sum of the lot. However – the voltage parameter of the group is the minimum value used. Furthermore, do not mix capacitor types.

For example – C1 is 10 uF, 63V; C2 is 470 uF 25V; C3 is 1000 uF 16V. With these three in parallel, the capacitance is 1480 uF; and the maximum voltage is 16 volts.

{Thank you readers for checking my maths! – John :) }

Capacitors in series

This is somewhat complex, but can be done!

Again, always use the same type of capacitor, and the lowest voltage rating applies to the entire group.

Smoothing DC current with a capacitor

When AC current is converted to DC current using a bridge rectifier (four diodes) the resulting DC current is not very smooth… that is the actual voltage changes between zero and the maximum over very short periods of time. A capacitor can be placed between the positive and negative rails immediately after the bridge rectifier to solve this problem. It does this by charging to capacity when the DC current is above zero, then when the voltage from the rectifier drops the capacitor supplies current, acting as a reservoir. This in turn maintains the supply voltage.

Using the circuit above, we will demonstrate the smoothing process in the video clip below. The first part shows the AC current on the oscilloscope; the second part shows the noisy DC current at the points 4 and 8 on the circuit above. Then a 470 uF electrolytic capacitor is inserted across points 4 and 8 – you can see the difference and how smooth the current has become. There is still a slight ripple, but I cannot show this due to the low resolution of my oscilloscope. When building a power supply, one would place the linear regulator after the capacitor in our example.

For the record I am working on finding a better oscilloscope… slowly!

Well that wraps up my introduction to capacitors. In the next fortnight we will look at another aspect of using capacitors in DC circuits, so stay tuned.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our new Google Group.

Otherwise, have fun and make something!

:)

Some information for this post is from: historical info from Wikipedia; various technical information and inspiration from books by Forrest Mims III;  tantalum and SMD capacitor photos from Farnell Australia.




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