Circuit board help -

[Robshaw]

Hello all,

I'm looking for some help if possible. Does anyone on here have any experience with Circuit boards and LED Diodes?

I want to do something really simple where I have two LED Diodes (one blue) and (one green) connected to a small circuit board... The blue led I want to light up when voice is detected. The green led I want to light up when listening/ no sound is detected.

Thanks in advance!

Rob.

[TeflonTom]

You could potentially do that with just a single npn transistor and a few resistors and a tiny microphone.

what you should do is see if you can find a prototyping kit that uses bread board and jumper wires and have a pay, you normally get a few resistors and LEDs and stuff in the kit and they aren't too expensive

edit; you could also use an operational amplifier ic too instead of a transistor, and have a variable resistor in a feedback loop to so you can set the sensitively at which the thing switches from one state to another.

Edited 27 March, 2012 by TeflonTom

[deecee]

Go to Maplins website you should find what you require on there

[Robshaw]

You could potentially do that with just a single npn transistor and a few resistors and a tiny microphone.

what you should do is see if you can find a prototyping kit that uses bread board and jumper wires and have a pay, you normally get a few resistors and LEDs and stuff in the kit and they aren't too expensive

edit; you could also use an operational amplifier ic too instead of a transistor, and have a variable resistor in a feedback loop to so you can set the sensitively at which the thing switches from one state to another.

If I said I have never touched on electronics before - That was brilliant, many thanks... Will start to gather some bits and bobs!

[TeflonTom]

http://www.ebay.co.uk/itm/ELECTRONICS-STARTER-KIT-ALL-COMPONENTS-NEEDED-START-ELECTRONIC-PROJECTS-/120843434456?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c22d479d8

this might be a good starting point for you, you get a breadboard and some jumper wires and a few LEDs etc.

[cheezemonkhai]

You should be able to drive the input from a serial/parallel port on your computer that is taking the input if you wanted to do that Rob

[VWD]

If I said I have never touched on electronics before - That was brilliant, many thanks... Will start to gather some bits and bobs!

Might I suggest some basic theory books, especially those explaining ohms law.Ohms law is the basis of all electronic calculations.You will need it to e.g calculate the series resistor to limit current to a LED. Too much ,and bang goes LED. Too little and LED might not light. It will help you understand te specs on componants like LEDs ,and how much power a resistor can handle .

e.g , LED has forward drop of 1.7 V at 15mA. Driven from 9v battery .

Voltage to be droped = 9-1.7 = 7.3v @ .015A. ( From Ohms law, V=I*R , R= V/I= 7.3/.015 = 486OHMS. Now resistors come in series.Nearest one is 470 ohm.

Power in resistor = Amps * Volts = 7.3*.015= .109Watts. So a standard .6W would be more than plenty .

That's what I meant about some theory.Might look complicated, but it all operates on a set of rules.

And a meter might be usefull. You can pick up digital ones for a few pounds. Beauty of the digitals is that you're not concerned with polarity. ( If you get a negative reading ,you've connected it wrong way round) . You could work out the value of a series resistor for a led and then check to see how well you've done the sums.Don't worry if the voltages/currents are slightly ( 10-20%) different ,the example above the current might be higher because of the lower resistor .

One last suggestion. When playing on breadboard add a series diode in the positive leg( something like a 1N4001) ,with the white band furtherest from the battery. It will (hopefully) prevent applying power the wrong way round. And lastly , electronics is infectious. I've been in the game for over 40 years ,as a hobby and professionally, and even with professional qualifications find there's always more to learn . If I can help pass on some theory ,PM me .

I did find a sound operated switch in an old magazine, but way too complicated .

Possibly as someone said, use an op amp ( with a variable resistor in the feedback loop as sensitivity ) and feed the output to a logic DEVICE, with two leds, one to supply and one to negative . . BLUE to supply, GREEN to negative . But you'd have to use something like a CD 4050 to drive the LED, AND pin all the unused inputs ,via a 1M ohm resistor to a supply line. Additionally, you'd have to use a static wrist strap to handle the device ,as CMOS IS STATIC SENSITIVE .

Enjoy.

Edited 27 March, 2012 by VWD

[Robshaw]

You should be able to drive the input from a serial/parallel port on your computer that is taking the input if you wanted to do that Rob

Somebody knows what I'm doing.

Thanks for all the help and suggestions. I have gone and got the breadboard kit and started some light bedtime reading.

[TeflonTom]

If any questions spring to mind then ask away, sounds like vwd is a bit of an electronics guru, and I'm a bit of a boffin too with that sort of stuff.. I build my own valve amplifiers at home

[Robshaw]

If any questions spring to mind then ask away, sounds like vwd is a bit of an electronics guru, and I'm a bit of a boffin too with that sort of stuff.. I build my own valve amplifiers at home

Why didn't you say? - Care to do it for me?

Waiting for the kit to arrive but sort of understand the post you made above. I'm sure I will come back to you with 59 million questions! Thank you so much folks.

[VWD]

If any questions spring to mind then ask away, sounds like vwd is a bit of an electronics guru, and I'm a bit of a boffin too with that sort of stuff.. I build my own valve amplifiers at home

Not really,but spent a long time in telecomms transmission maintenance where at first all was valve based .First time in my life I really enjoyed my job.

When I first did my C &G ,there was no mention of transistors. It was all valves . As transistor stuff came in ,I picked it up on training courses . ( After all a transistor is basically a triode, with the electrodes given differing names ,and operating at a lot less volts than most valves).I've been back to college once or twice .I gave rob an example of how to work out the correct operating conditions for a LED as an example , to demonstrate that some of the theory is not difficult to apply, once you understand the basics . ( As you'll know if you're into valve amps) .

Teflon - site that site interest you is http://www.vintage-radio.com/- all about ancient radios, but a lot of blokes that know about valves and circuits.

Edited 28 March, 2012 by VWD

[Robshaw]

Okay, so I was doing pretty well untill I tried to go it alone. I found the following diagram:

The Circuit is designed to make the LED's blink on a timer.... I have the following and trying to mix/match to the diagram got me confused.com damn dyslexia... Can anyone help me out and simply this for me please?!

[TeflonTom]

ok, firstly do you know how the bread board works? looking at that circuit, basically one or the other Of LEDs will flash, it's what's called astable, the variable resistor which is the component r2 will set the speed at which they alternate.. R3 and r4 are there to protect the LEDs from too much current.

The major component you have there is the 555 chip, the pins on those are arranged not in the same layout like it is shown on the diagram above.. There will be a dot or a semicircle marking at one end or one corner, this tells you where pin 1 is and the pins go in an anti clockwise direction from there.. If you look on google you will find a pin out diagram for that chip fairly easily..

My next question is do you know how to identify resistors using their colour codes and coloured bands?

[VWD]

As Tom says, the IC pins are not as per schematic.

Try this for examples of pinouts of various IC. Some have a dot beside pin 1( as the 741,), others have just a cutout on the end.In this case pin 1 is the left pin ,looking from above . http://www.hobbyproj...ic_pinouts.html

Now resistors and colour codes .There's the older three band system( not see a lot these days ) and the modern 5/6 band system . As most resistors these days are .6W metal film ,they will be 1% . Temperature co efficient is only applicable in circuits where any drift with temperature could cause problems ( so ignore for your purposes) .There's also a nice set of FAQ.And a look /explanation of resistor series .

http://www.hobby-hou...calculator.php.

I've also got a nice little explanaiton of how a 555 astable ( two state operation) works, if I can get my scanner installed on Win7 64bit(. Need some new drivers . ) ,I'll scan it in . Got a full 13 page of A5 ,on the 555 ,with circuits, but no idea how to put it up for private viewing, so as not to infringe copyright( and possibly have mods getting inflamed) . Any suggestions?

Edit - just seen that I can PM images . So when I can scan the pages in - I will . It's quite easy going stuff . With a few diagrams and such like .

Also edit , something that helps with resistors is having a cheap DVM.Pick a resistor and using the chart ,attempt to work out value . Then measure .

But as I said earlier, when breadboarding /prototypeing, it's easy ,even for old hands to get the power supply leads the wrong way round. My suggestion is to fit a diode before the +ve rail on the breadboard ,in normal direction of current travel . Connect power wrong way and diode blocks current flow, preventing nasty ( even expensive smoke) .

For drawing my own schematics ,I use a free download -PCBEXPRESS ( .COM) .It's in two parts, schematic and PCB.So you can re draw the schematic to make it easier to read, and in PCB MODE .Handy even for breadboarding, and if you want to make a vero board version - equally usefull. Jist be aware ,that ,if you go down the make a PCB ROUTE, that you wil be looking at the other side of componants( i.e the underside connections,needing you to think in another mode).

For a normal( not cmos/low power) 555, performance may be unreliable if values are outside the following-

Resistance =1kohm to 3.3 Mohm

Capacitor= 470 pf( pico farad .1pf = 10exp -12 farad) to 470 uF ( 1 uF = 10 EXP -6 Farad) .

And another common capacitance value is the nanoFarad. ( 1 exp-9 Farad) .

Another thing about the 555 - the duty cycle ( time on /off ) can never be less than 1. But if you play around with values, making the resistor( R2 in your drawing) much larger than R1, it's possible to approach this . There's other ways of doing this .

Edited 30 March, 2012 by VWD

[TeflonTom]

Sorry I forgot to mention, an led is a type of diode, the current will only flow though a diode in one direction, see the circuit diagram symbol on one side it has a flat line, on the led itself this will have a slightly shorter leg..

when I get a chance tomorrow I'll try and draw up or maybe indeed actually make up this circuit and take some pictures to show you how to do it.

[David 8]

Jesus Tom is there any thing you don't know ?

[TeflonTom]

Jesus Tom is there any thing you don't know ?

no... Hth

[Robshaw]

Sorry I forgot to mention, an led is a type of diode, the current will only flow though a diode in one direction, see the circuit diagram symbol on one side it has a flat line, on the led itself this will have a slightly shorter leg..

when I get a chance tomorrow I'll try and draw up or maybe indeed actually make up this circuit and take some pictures to show you how to do it.

You sir are a star! - I think I owe you and VWD some beer tokens.

I'm sorry for being a tad 'slow' on the uptake, never done this before

[VWD]

You sir are a star! - I think I owe you and VWD some beer tokens.

I'm sorry for being a tad 'slow' on the uptake, never done this before

Not slow - Tom & i have done this for years(from my understanding of Tom'S CREDENTIALS). I'm only trying to help out. But to get from "SLOW" to HND standard , takes Years. I've gotten there via years of experiance. Any one wanting to learn - I'll try to help, but I'm not the best instructor in the world. But fire away- I'll always try to help .

[TeflonTom]

right then, first you need to understand how the breadboard works... you have a very basic one which is good

The holes in the board are connected my a metal bar internally, with a gap in the middle, ive drawn this with the battery connected up, this means that everything on that top left line is + voltage from the battery, everything on the bottom left is ground or - from the battery....still following?

edit: something not quite right with my browser, not sure if this came out alright

[Robshaw]

right then, first you need to understand how the breadboard works... you have a very basic one which is good

The holes in the board are connected my a metal bar internally, with a gap in the middle, ive drawn this with the battery connected up, this means that everything on that top left line is + voltage from the battery, everything on the bottom left is ground or - from the battery....still following?

edit: something not quite right with my browser, not sure if this came out alright

Yep following.... All came out right.

Loving the paint skills but it's what's needed for me to get a good basic understanding

[TeflonTom]

try that mr robshaw

[VWD]

Board I've got has two rails down either side for supplies . Otherwise it's same as shown . But again, can I suggest replacing the link fom the battery with a diode .( For robs benefit) -A diode will only conduct in one direction . If you inadvertantly cross the supply rails , then no voltage will flow into the circuit. And in a circuit with semiconductors/IC ,reverse polarity will produce smoke + heat = either open circuit or short circuit ,but certainly not semi conductors .

I've just noticed a couple of things on the circuit diagram ,which need adding. I've drawn a layout/schematic( showing pin out/ componant placement ) with these two items added .

First item is C2 .On the standard 555,it's needed to stabilise the control voltage function. On the low powered ones its not needed .C3 is needed to decouple the + rail( prevent switching surges getting back to other circuits).Typical values are as per diagram .NB- the voltage rating of C3 needs to be greater than the supply, other wise it can go bang . I've also added a protection diode ( the idea is to stop a reverse supply wrecking the componants) .

[TeflonTom]

ah yes there is some diodes there in that pic above... dont want to confuse the lad yet though....

ive got a proper breadboard with d type connectors, and multi voltage rails etc but i didnt want to break that out to simplify it, his board doesnt appear to have bus rails on it..

[VWD]

ah yes there is some diodes there in that pic above... dont want to confuse the lad yet though....

ive got a proper breadboard with d type connectors, and multi voltage rails etc but i didnt want to break that out to simplify it, his board doesnt appear to have bus rails on it..

I know, but the protection diode is good practice for protyping. Especially for newbies, where if it's fitted, there's less chance of a mistake, and then they've got the extra problem of fault finding,not knowing if they've damaged anything( and if they have , what any tests would show). The idea of a mixed diagram, was to show how things got connected .

All of the kits will provide a NE555, almost indestructable with handling ,as opposed to other varieties. And it will give 200mA ( SINK /SOURCE) ( For Rob, that's if output from 555 is high( 6v ) ,then circuit is via r4/d3 to ground. If output low, then circuit is via R3/D2 TO +VE LINE,giving a max current of 200mA n either direction) .

I've got some theory notes scanned in ,but my ISP is playing silly Bs on letting me upload them to Photobucket . It's just general stuff on terms to do with Astables, and some mild theory on the 555 astable .like how to calculate values to get the frequency you want, and a description of how the thing works .My engineering training was geared toward, first understand how it works, then if it stops working ,then find out what is not working, and you've almost solved the problem .

If I get a chance, I might get the nonogram scanned. That gives an idea of R1/R2/C values for any frequency ,subject to the values I put up in post 14 .