COLIN WONFOR: Breaking the rules – part #01

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The title of this article may seem strange to some of you. Let me explain. I want to share DIY tips and related info you’ll you not find anywhere else or, at least, not easily. This series of articles has been prompted by the questions I received and answered I provided during the launch of my DIY kits. http://forms.aweber.com/form/42/907241042.htm

Clearly, quite a few of you out there wanted to do dip your toe into the high-end DIY world - recognising the potential for fun and personal achievement and of course …. GSFPM or in other words, great-sounds- for-peanuts-money. Also clearly, many were nervous having not done this sort of thing before or if they had, far too long ago to remember the outcome. So, this is me with a kindly teacher’s hat on. So class – are you sitting comfortably. Hey, you at the back, yes – you. Pay attention!

Let’s start at the beginning.

My very first solid recollection of making electronic devices was with my Grandfather John William at 12yrs old. He and I made our first valve (tube) radio a single tube device. A I’d made other things like crystal set with my dad Tony but these memories are fading. I do remember being a naughty boy though. That’s because I electrocuted my poor younger brother Andrew at 7yrs old with a 90V battery. Whoops. Not fatally though. He’s still with us, now 57yrs old. He’s has not forgiven me.

Now let’s get started and consider basic things. For some of you, it will be simple and you would have done this during secondary school physics. For others though, what follows here will seem hard. My message is …. “hang in there guys you will get there and kits and fun projects to make will be yours and for your kids.”

Resistors

Some of you will recall Ohms Law but may not recall the vital colour code readings. I have worked with many engineers that still, after many years away from college and uni, could not read colour codes. And often they didn’t see the point of learning them! That attitude is in my view both misguided and wrong.

So let see:-

These charts are available in lots of place on the internet so if you lose this do not worry. This circuit is a working basic mic amp.

You can see the resistors R1 at 1.5MΩ and R2 at 10KΩ. Question: What is the colour code for various tolerances of resistors?

  • Let’s start with R2 at 10KΩ at 1% = Brown, Black, Black, Red and tolerance band 5 is Black
  • OK so we get 1,0,0, and 2 more 0 followed by 1% = 10,000 Ω or 10KΩ
  • OK now for the hard one R1 at 1.5MΩ at 1% a 5 band type we have 1,500,000Ω
  • Giving us Brown , Green, Black, Green followed by in band 5 Black and we have 1,500,000Ω
  • To make it Mega Ohms we divide by 1,000,000 and there is 1.5MΩ at 1%

OK the symbols in the MIC circuit. The resistor often drawn as this :-

But more often here in the UK as this:-

All resistors have a maximum power rating from a few micro watts through to kilo watts. This is very important when choosing your resistor type. Q1 is a transistor symbol; this type is a NPN and this particular one is a general purpose low power type:-

We’ll be playing with other types later and my guidance will include all sorts of different functions, from DC to VHF and including Power and Audio.

The next symbol is another passive device, like the resistor, whereas the transistors are known as active devices. More on those later. The Capacitor; there are thousands of different types. For now though, our symbols will show the type we are using in the circuit.

V1 is a battery it could be our old PP9 style from a radio or a bank of AAA @ 1.5V each.

Here is the symbol. Note it says 9V not 90V. OK?

And now, our last symbol. This could be a signal generator a power supply, a square wave/pulse generator. The clue to its function is the writing.

It say SINE(0 10mv 1KHz) which, when translated, says I am a sine-wave generator producing a 1KHz signal at 10mV with 0 DC offset.

Now you will need to download this software from LTC via the link below. It will let you run the MIC circuit above in a simulation. You can change the parts and look at the wave forms. This is what I got on the terminal labelled OUT.

Links:- This is the section you need.

LTspice is a high performance SPICE simulator, schematic capture and waveform viewer with enhancements and models for easing the simulation of switching regulators.  Our enhancements to SPICE have made simulating switching regulators extremely fast compared to normal SPICE simulators, allowing the user to view waveforms for most switching regulators in just a few minutes. Included in this download are LTspice, Macro Models for majority of Linear Technology's switching regulators, over 200 op amp models, as well as resistors, transistors and MOSFET models. 

LTspice for Windows 7, 8, and 10 was updated on May 22, 2017 and includes all recent models.

Support for Windows XP version has ended and will no longer be updated.

http://www.linear.com/designtools/software/#LTspice

I have nearly completed the next lesson in this series.

Thank you class.

Class dismissed

CW

colinwonfor@gmail.com

 

 

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Please click HERE to view the growing vault of Colin's answers

If you have a question for Colin then please contact him as follows: cj14wonfor@gmail.com

 

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