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61  Using Arduino / Project Guidance / Re: Arduino fire alarm notification on: August 10, 2014, 07:43:51 pm
I was assuming you were using 240v alarms....compulsory here in Aus..... smiley-mr-green

Uh what they are!?! Omggggg I'm gonna die!!!!!

Suppose the fire breaks out at the fuse box or in a backroom the smoke alarm does not go off but the fire trips a fuse killing the detector...

I'm off to buy a battery operated one!
62  Using Arduino / Project Guidance / Re: Can two Arduinos read one sensor? on: August 10, 2014, 07:37:33 pm
If the sensor produces purely voltage eg 0v off 3v half flow 5v full flow etc... then yes

If the sensor has 2 or more pins, have both arduinos flag a single pin high...  then check the status of the pin before attempting to read the sensor?
63  Using Arduino / General Electronics / Re: Dual voltage 9 and 12 volt nominal input on: August 10, 2014, 07:30:36 pm
How are you powering the leo? It has a usb pcb shaped plug which requires 5v...

First step down the voltage via a regulator, switching or 7805, power the leo with that.
Secondly, a voltage divider to knock down the max potential voltage (15v) to 4.5v

64  Using Arduino / General Electronics / Re: High Voltage swich with IR Sensor on: August 10, 2014, 07:24:05 pm
How high is this voltage?

The higher the voltage the more you need to worry disspating wasted energy, a switching regulator..  lack of info
65  Using Arduino / General Electronics / Re: How to design efficient electronic switch on: August 10, 2014, 04:16:46 am
Using a comparitor would be ok, they require a little current.

But using a transformer from the ac source to boost the voltage should work.
66  Using Arduino / General Electronics / Re: Protecting diy pcb boards.... on: August 09, 2014, 09:48:37 pm
Oh nice!  Better than covering the entire board, thanks!

I guess an even spread/layer of solder paste would do in an emergency ..

67  Using Arduino / General Electronics / Re: Beginner Soldering iron Choice on: August 09, 2014, 09:44:41 pm

I've destroyed many ESD sensitive devices because the soldering iron was not ESD safe...  since switching to the cheap atten models which are temp controlled, not one single issue since smiley

68  Using Arduino / General Electronics / Protecting diy pcb boards.... on: August 09, 2014, 09:30:51 pm
After etching, any suggestions on protecting the copper tracks from oxidizing?  (Since these boards don't have a silkscreen)

Varnish? Lacquer?  Glue?   

69  Using Arduino / General Electronics / Re: general question about PUT transistors on: August 08, 2014, 11:10:25 pm
Since this is about learning....

This is one of the first oscillator circuits using transistors...
70  Using Arduino / Audio / Re: Difference between two circuits on: August 07, 2014, 11:48:07 pm
That explains that....

So what explains the use of the opamp symbol on almost every circuit I've cime across?
71  Using Arduino / Audio / Re: Difference between two circuits on: August 07, 2014, 10:41:27 pm
The lm386 is amplifying and driving the speaker...

Does the sparkfun have an amp or preamp circuit? It should or the tiny voltages on the mic will be too small to be read...

So then, how much gain do you need.... eg do you want to get around 500-700 with normal speech or do you want 100 - 200 for normal speech so you hit 900-1000 for loud noises for example, or do you want 800 - 900 readings for whispers...

The lm386 is default around 20? Gain unless you set it externally via resistors/caps  the lm386 is weird to me as most opamps use a resistor divider to set the gain, yet the 386 a capacitor can adjust the gain.. I'll have to look into that sometime
72  Using Arduino / General Electronics / Re: Switching Power with 2N2222 Transistor on: August 07, 2014, 09:30:39 pm
Duue to the size of the pictures it's hard to tell on my phone.

A schematic is better.


The image loaded!  You have 5v going to the collector then out to the emitter!  Plenty of voltage loss.

Instead, you should either switch to a pnp or, on your npn...

emitter to ground
Collector to the negative terminal, eg - of your led.
+ of your led to the 5v rail
Base pin to your button.

The transistor completes the path from the positive terminal of say your led through the collector to the emitter to gnd.


You NEED a resistor (s) on the base and maybe between collector/emitter depending.
73  Using Arduino / General Electronics / Re: controlling 12v LED with arduino -- pwr supply question on: August 07, 2014, 09:16:29 pm
If the 7805 is feeding into vin, the regulator must be supplying around 3v to Arduino..

The 7805 should go to 5v....

74  Using Arduino / General Electronics / Re: How to design efficient electronic switch on: August 07, 2014, 09:02:46 pm
@Tom - it's coming from an old diskman. I want it to make the leds on when i hit play

Is it coming from the headphone socket?

That will be audio/AC and it will be more than 0.5V, how and where did you measure the 0.5V?

Tom..... smiley

Rectify it, store it in a small .1uf? Or so cap then use that pulse to latch your circuit (via feedback) or a flip flop, but I think I came across a circuit ages ago that simply powers on your device when it sees a signal...

And again why can't you use the 5v source? Amplifying the signal would be easy.
75  Using Arduino / General Electronics / Re: general question about PUT transistors on: August 07, 2014, 08:51:45 pm
If all it is you want to do is flash an led..

This is the cheapest (? Maybe component wise) circuit.. I'm just wondering if the 555 is a cheaper ic, however the 555 requires more external components.
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