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1366  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Common electronic parts to have on hand on: July 31, 2010, 03:00:17 pm
I've spent the best part of 50 years trying to answer that question for myself and have drawers full of "readily available and useful" bits that I have never - and probably never will - use.

Find yourself a handy and speedy supply source and only buy what you really need plus say 10% for "spares"

1367  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: transistor or MOSFET?? on: July 02, 2010, 12:44:27 pm
Given the simple yes/no question then go for the mosfet.  Transistors, if not fully turned on, can dissipate a fair amount of heat.  Mosfets are either on or off and have extremely low on resistance to dissipate little heat.
1368  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Resistors - When to use and how on: June 28, 2010, 03:07:26 am
The simplest explanation I can think of is to consider the resistor as a current limiting device.   A bit like a tap (faucet) in a water pipe.

It really depends upon the application as to whether you need a resistor or not.  Many devices have input/output resistors built into them in which case an external resistor shouldn't be required.

If you are unable to determine if one should be used, have a look at other peoples example circuits and you may find one similar to your own - did they use a resistor - ?

1369  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Soldering on: June 14, 2010, 07:36:28 am
I have always found Antex irons of very good quality with a good range of tips - all available from maplin.

The one I use for electronic work is rated at 15watt and does everything I need.  If you go for one, also buy the  spring style stand c/w sponge.

Maplin also sells a rather expensive temperature controlled iron/soldering station for a penny short of £70 which gets good reviews.  Haven't yet drummed up the courage to buy one

1370  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Soldering on: June 12, 2010, 01:05:34 pm
I must admit I used to use the leg of my jeans until my wife asked what all the silver streaks were.  
Forgot to mention previously that, if you use decent flux cored solder, you should never need to file the iron bit.  Many bit manufacturers offer coated bits to improve performance and minimise erosion, which would be eliminated after the first filing.  There was (still is ?) a solder called Savbit, the flux of which was aslo designed to prevent bit erosion.

1371  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Soldering on: June 11, 2010, 03:08:30 pm
You should never need extra flux if you are using rosin cored solder, since all surfaces should be clean enough.
Emery will be too abrasive on circuit board, an old typewriter eraser or a "plastic" pan scourer should be more than enough to clean any oxide film off the copper.  A quick rub to raise a shine is all that is required and ensure all plastic or rubber residue has been blown off before commencing soldering.
Most soldering problems with electronics will be down to having a dirty iron tip.  I recommend a wet flat sponge as supplied with soldering iron stands and wiping the tip between joints.  Keep the tip nicely clened and always having a film of shining solder on it.  If it gets dull, the solder is wasted, needs wiping off and retinning.
Touch iron to the junction of the circuit board and component simultaneously.  then offer solder to the tip face, solder should immediately melt and flow to both surfaces, lift off iron.  It is essential that the solder is set before moving the joint - only takes a second.
Another common error is to use solder of too large a diameter.  For delicate electronics use the thinnest you can get.  It MUST be resin (or rosin) cored.
1372  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: how to use 8 of the digital i/o pins at same time? on: June 13, 2010, 01:06:40 pm
But the question related to Arduino - not some device that might stretch our personal (or national) budgets.
Basic question still stands - what do you mean by simultaneous
"exactly so or just about so"
1373  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: how to use 8 of the digital i/o pins at same time? on: June 13, 2010, 04:04:48 am
It depends on what you mean by "the same time"
Surely any processor can only operate on one instruction at a time (and that includes the best proecssor of all  -  the human brain) and as such no two events can occur simultaneously.
This "drawback" is used effectively in programmable control systems to ensure "simultaneous" sequences occur in the correct order
However you can surely produce a routine to set up and then switch outputs on a single given command - but even then events will not be exactly simultaneous
1374  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: RGB LED Question on: May 11, 2010, 03:48:21 pm
Perception of vision or colour is your brain's interpretation of what the eye sees.
If you look closely at an old style TV set with a trinitron or shadow-mask tube you'll also see the three primary colours which when viewed at a sensible distance will make up the correct balanced colour.  
RGB LEDs are three separate units combined in a single capsule, not some magic piece of crystal that generates a single colour from a triple input.
1375  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Measuring Current on: April 20, 2010, 02:04:45 pm
I don't wish to sound negative, but if i was asked which was the most unsuitable instrument to measure slow changing DC variables, I would have to say an oscilloscope.

As others have alreay said a couple of half decent digital meters would far better meet your need.  In fact, for measuring the step changes of current you might want to consider an analogue meter.

1376  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Virtual Breadboard on: April 19, 2010, 06:47:34 am
Try the following :

A bit old but hopefully better than nothing

1377  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: uni watch project similar to LED pocket watch on: April 14, 2010, 01:11:05 pm
should have mentioned that 32768 is 2^15.  so if your RTC divides the basic crystal frequency using a suitable set of binary dividers you end up with 1 pulse/second   Simples
1378  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: uni watch project similar to LED pocket watch on: April 14, 2010, 01:04:28 pm
The 32.768KHz crystal is the value that you use to built an RTC (real time clock).  Once you've built that (it features on other sites) you apply it's pulse (1 per second or whatever) to the Arduino from which you then generate the display.

Try googling RTC and you should get suitable circuits

1379  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino and Xbee for Wireless Data Transfer on: April 10, 2010, 02:55:43 am
Surely resolution is a function of ADC conversion bits and has nothing to do with measured voltage range.  1x10E-10 of 3.3volts has exactly the same resolution as 1x10e-10 of 5 volts
1380  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Coffee Level Sensor on: April 07, 2010, 03:01:38 pm
Don't wish to spoil anyone's fun but, isn't this just a little bit silly.  
May I suggest a) a glass coffee pot or b) looking inside the pot
As a professional engineer I'm all for inovation, having fun, and doing things just for the sake of it, but there are limits.

Perhaps you could fit a small gamma source to one side of the pot and fit suitable sensors to the opposite side.   Or a temperature profile monitor down the pot side.  Either of these brilliant (but equally stupid) suggestions will detect the interface between coffee and air.  

OK I'm a boring and grumpy old git.
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