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Δευτέρα, 24 Νοεμβρίου 2014

How to fix the DT830D multimeter. (resistance and diode problem)

Twenty years ago I bought my first multimeter a Chinese-made DT830D.I was not into electronics then.In fact it wasn't until rather recently that I started tinkling with circuits. It was more like the desire to learn electronics one day that made me buy it back then.

the legendary Chinese multimeter
Anyway,that multimeter was still working until recently when it developed a problem-it could measure resistance.Here are the symptoms it had.

The symptoms

  • At first, it could not measure small value resistors like 10ohms.The meter was fluctuating around 10 dislaying 12 ,9,8,sometimes 10 ohms and never stabilizing.All the other measurements of bigger size resistors seemed fine.
  • the diode meter did not work at all
  • Later on it could measure resistance at all zeroing out the number on the LCD.
So,I decided to have a look inside.When I opened it  a rather big scorched resistor could be seen right away.It measured 90K.

the culprit
I did a net search and came across a post in a Russian forum.It suggested the resistor R5 should be replaced with a 1K value one.The model of the multimeter was the same but a much newer version with smds.

I replaced the resistor with the first 1K I could find and that was it!It worked!Now the old multimeter is working measuring resistance correctly.On top of that the resistor fixed and the diode function problem.I am not sure how the resistance and the diode functions are connected with this particular resistor.

the fix
replace the resistor in the images for a 1K  new one.


Here is the new 1K resistor in place.

Schematic
Schematic of a similar multimeter model DT830B here.


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Τετάρτη, 19 Νοεμβρίου 2014

My first small Tesla coil with NE555 and flyback transformer.


This is my first Tesla coil.It's not completed yet actually.

Now all I need is to produce constant sparks off the top of the coil without touching a screwdriver or a lamp! I've tried some aluminum foil on top of the coil but nothing happens.How can that be done?A spark off the top without touching anything?Any suggestions?


Here I've used two separate power supplies-a 6V powering the NE555 and a 12V powering the 2N3055 and the flyback.I've also used a COSMO 1010 (C1010) photocoupler to make sure that the NE555 doesnt blow from the 12volt supply.

the coil
The secondary coil has about 400 turns of 0.4mm magnet wire wrapped around a 3cm paper roll.The primary is 5 turns of speaker wire.

the spark gap
Just two screws not attached to anything facing each other.

capacitor bank
Here are the capacitors I've used:
5̶3̶2̶J̶,̶ ̶4̶7̶4̶J̶,̶ ̶.̶2̶7̶J̶ ̶,̶ ̶.̶6̶4̶J̶,̶ ̶.̶2̶2̶J̶,̶ ̶1̶0̶5̶J̶,̶1̶2̶4̶J̶,̶ ̶8̶2̶2̶J̶/̶1̶.̶6̶K̶V̶.̶M̶o̶s̶t̶ ̶o̶f̶ ̶t̶h̶e̶ ̶o̶t̶h̶e̶r̶ ̶c̶a̶p̶s̶ ̶a̶r̶e̶ ̶r̶a̶t̶e̶d̶ ̶4̶0̶0̶V̶o̶l̶t̶s̶ ̶I̶ ̶t̶h̶i̶n̶k̶.̶O̶n̶e̶ ̶o̶r̶ ̶t̶w̶o̶ ̶2̶0̶0̶V̶o̶l̶t̶s̶.̶
S̶o̶ ̶,̶i̶f̶ ̶m̶y̶ ̶c̶a̶l̶c̶u̶l̶a̶t̶i̶o̶n̶s̶ ̶a̶r̶e̶ ̶c̶o̶r̶r̶e̶c̶t̶ ̶t̶h̶e̶n̶ ̶t̶h̶e̶ ̶b̶a̶n̶k̶ ̶s̶h̶o̶u̶l̶d̶ ̶b̶e̶ ̶a̶b̶o̶u̶t̶ ̶4̶K̶V̶o̶l̶t̶s̶ ̶a̶n̶d̶ ̶9̶0̶0̶ ̶p̶F̶s̶.̶.
The calculations were wrong -this was too much capacitance.I've replaced this chain of capacitors with a single DIY aluminum foil and plastic sheets as dielectric capacitor.I am not aware of the capacitance value of this though.I do not own an LC meter.

Here is how I made this homebrew capacitor.



Or not.
Maybe the bank is not good enough for spark on top.Maybe the bank is the culprit.

How to get the constant spark on top?

I know it has something to to do with resonance.Obviously there is no resonance here.





Here is the schematics I've used for this coil.



I got the schematics from here.

arximastoras.blogspot.com
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Κυριακή, 16 Νοεμβρίου 2014

Σάββατο, 15 Νοεμβρίου 2014

12Volt/1Amp DIY power supply!

I've recently built a very simple 12V/1A power supply using a UA7812 and very basic components. It powers my DIY speaker containing a TDA2003 amp pretty well !



Here is the components I've used :

-a 20v transformer (this one I got from an old casette player)
-Four diodes for the rectifier.Mine are big ones but anyone from 2N4001-2N4007 will do.
-A 2700uF electrolytic capacitor placed after the rectifier bridge.
-a UA7812 transistor.You can also use an LM7812 or any other 7812 transistor.
-a 100nF film capacitor to dump the high frequencies to ground.It is connected from the output of the transistor to ground.

You can leave out the metallic box I've used from a broken supply.
This is a very basic power supply circuit with the minimum of components.
And that's about it.

Here is the schematic.



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Παρασκευή, 14 Νοεμβρίου 2014

Easiest circuit for begginers in electronics-Lighting a LED!


Here is a great and very simple circuit for beginners in electronics that lights a LED lamp!

All you need is a LED,a battery and a resistor


If you don't know which LED leg is positive and which is negative there is a very easy way to find out.

Look into the LED-the big lead is negative (Ground) .Ground connection always have to be bigger.Many problems arise in circuits because of bad grounding.

Here is a blow-up of a LED head.

the big lead is negative


Some science
Now let's go into some more detail.You need a resistor to light the LED and to protect it from excessive current.

resistor value
How to calculate the resistor value.

Simple.Using Ohm's Law V=IR or R=V/I.
An extended form would be R=V1-V2/I.

or resistance=sourceVoltage -LEDvoltage/LEDcurrent

Red LEDs have about 2 volts and their forward current is 15 miliAmperes or 0.015 Amperes.Other LED colors are rated different.

The battery we use here is 9 Volts.

So ,replacing the formula for these values we get

R=9V-2V/0.015=466.66667 or 467 ohms for the resistor.If you cannot find a resistor of the exact value then pick one with the next closest value.It will do.

resistor Wattage
Now we need the resistor Wattage.
ResistorWattage=sourceVoltage -LEDvoltage x LEDcurrent
R=9V-2Vx0.015=0.105 which means that 1/4 watt resistor will do.

Resistors come in various wattages 1/4, 1/, 1/2,1 watt,2,5,etc...

calculator
If you still cannot get it try this online Ohm's Law resistor calculator.

arximastoras.blogspot.com
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Σάββατο, 1 Νοεμβρίου 2014

How I fixed a blown blender (thermal fuse).

Recently my neighbour brought a blown blender.It did not have power at all.So ,I opened it up to have a closer look inside.There are not much parts it the blender-some diodes and capacitors.I checked for continuity and power in various places and nothing seemed to be wrong.I got power right to the windings of the DC motors.



Nothing seemed to be wrong.I thought it must be the motor.So,I decided to have a look inside and started unwrapping the yellow tape around the windigs.Fortunately ,I didn't to unwrapp much -just half a turn- and voila.

a thermal fuse on a transformer
There it was hidden under the transformers yellow tape a THERMAL FUSE.I checked for power right before the fuse and it was ok-240Volts.Then I did the same after the fuse and I got zero power.I figured if I shorted the two ends of the fuse the motor should start.I took a small screwdriver and shorted the two ends and gues what-the motor kicked!

This little thing called a thermal fuse was the culprit.I did not have this kind of fuse to replace it and I used an ordinary 250V,5amp fuse for the time being until I get a proper thermal fuse.  


an ordinary 250V 5amp fuse

Nowadays most of the tranformers come with a thermal fuse.The problem is that sometimes they hide the fuse under the windings and you have to take the transformer apart in which case you're...screwed.

Cheers!
arximastoras.blogspot.com
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Τι σημαίνουν οι ενδείξεις των ελαστικών.




Όλα τα ελαστικά των οχημάτων αναγράφουν στο πλαϊνό τους τμήμα μια πλειάδα από αριθμούς και κωδικούς, τα οποία δείχνουν τις διαστάσεις, τις προδιαγραφές του ελαστικού την ημερομηνία παραγωγής κ.ο.κ. Ας δούμε λοιπόν ένα – ένα αναλυτικά τι σημαίνουν τα... ιερογλυφικά των ελαστικών. Παράλληλα για να δείτε τους τύπους των ελαστικών αλλά και τι σημαίνει η ειδική σήμανση - ετικέτα πατήστε εδώ.
Διαστάσεις
Παράδειγμα: 165/65 R14
Το 165 σημαίνει το φάρδος του ελαστικού σε χιλιοστά, το 65 είναι η σχέση ύψους προς φάρδος διατομής (65%), R σημαίνει δομή (Radial) και το 14 είναι η διάμετρος της ζάντας σε ίντσες.
Δείκτης φορτίου και πίεση αέρα
Στην φωτογραφία αναγράφεται μέγιστο βάρος ελαστικού στα 437 κιλά (ή 963 λίβρες) και μέγιστη πίεση στα 51 PSI ή 350 kPa.
Ημερομηνία κατασκευής
Ο τετραψήφιος αριθμός της φωτογραφίας υποδηλώνει την ημερομηνία κατασκευής του ελαστικού. Δηλαδή: Το 3612 σημαίνει ότι το ελαστικό κατασκευάστηκε την 36η εβδομάδα του 2012.
Δείκτης ταχύτητας
Στην εικονιζόμενη ένδειξη 79Τ, τα νούμερα αντιστοιχούν με το δείκτη φορτίου (το 79 αντιστοιχεί με 437 κιλά) και το γράμμα με το δείκτη ταχύτητας. Πιο αναλυτικά:
  • L έως 120 χλμ./ώρα
  • M έως 130 χλμ./ώρα
  • N έως 140 χλμ./ώρα
  • P έως 150 χλμ./ώρα
  • Q έως 160 χλμ./ώρα
  • R έως 170 χλμ./ώρα
  • S έως 180 χλμ./ώρα
  • T έως 190 χλμ./ώρα
  • U έως 200 χλμ./ώρα
  • H έως 210 χλμ./ώρα
  • V έως 240 χλμ./ώρα
  • W έως 270 χλμ./ώρα
  • Y έως 300 χλμ./ώρα
  • ZR > 240 χλμ./ώρα
Κωδικός έγκρισης
Ε2:  Ένδειξη συμμόρφωσης με κανονισμούς της ΕΕ. Ο αριθμός στον κύκλο μετά το E δείχνει τη χώρα έγκρισης.
Tubeless Radial
Tubeless σημαίνει χωρίς αεροθάλαμο (κοινώς σαμπρέλα) και Radial σημαίνει ότι ο κορμός αποτελείται από ακτινικές χορδές λινών. Αυτές οι χορδές είναι στρώματα υφάσματος που συγκροτούν τον κορμό του ελαστικού, και αναπτύσσονται ακτινικά κατά πλάτος του ελαστικού από τη μία στεφάνη στην άλλη. 

http://www.autogreeknews.gr/

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