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31  Using Arduino / General Electronics / Transistor, PWM and LEDs on: June 02, 2012, 06:10:00 pm
--edit: see http://arduino.cc/forum/index.php/topic,108403.msg814896.html#msg814896 for up to date info

Hi all,

I'm doing some experiments to better understand how to use transistors as amplifiers in future projects.

Right now, I have this:


But with this setup, PWM works in a very strange way.
Code:
analogWrite(ledPin, 0);
makes the LEDs super bright and
Code:
analogWrite(ledPin, 255);
turns it off.

On a single LED that is not on the resistor, 0 = off, 255 = full brightness.

Why is that? I guess the transistor is inversing the PWM's effects?
Should I carry on, using PWM with reverse values (ie 255 = off and 0 = full on) or does the transistor have other side effects on PWM?

Thanks!

--edit: see http://arduino.cc/forum/index.php/topic,108403.msg814896.html#msg814896 for up to date info
32  Using Arduino / Project Guidance / Re: DIY home automation and data transmission on: May 27, 2012, 12:38:21 pm
Nice. Would you recommend them?
33  Using Arduino / Project Guidance / Re: DIY home automation and data transmission on: May 27, 2012, 07:30:55 am
The jeelab wireless node seems very interesting, coupled with a digital potentiometer and/or a relay. Thanks!
What is the real world range of these 433Mhz transceivers?
34  Using Arduino / Project Guidance / DIY home automation and data transmission on: May 26, 2012, 06:34:51 am
Hi all,

I am looking at the feasibility of a DIY home automation system using an arduino. Because I am renting the place, I want to avoid doing any wiring. Is there a way to transmit data over powerlines? I read about X10, infiniteon etc but these seem to come as preassembled devices that are not so flexible.
I'm not looking for a complete system but rather a modem to transmit the data of sensors and actuate outlets accordingly. Will I have to go wireless with a 433Mhz system and a micro controller in each of the items to be controlled?
35  Using Arduino / Project Guidance / Re: General project planning methodology? on: May 05, 2012, 08:16:26 am
Thank you for your interesting answers!

I am trying to put together an automatic plant watering system that will use recycled rainwater. I was thinking about using gravity to pour the water and use a small water hose on a gliding rail to move from plant to plant in a linear fashion with a valve to control the water flow. But I'm kind of going in every direction without anything concrete to really start on simply because I didn't know where to start.
I will try to apply what has been said in the posts above and see if I can get something done smiley
36  Using Arduino / Project Guidance / General project planning methodology? on: May 04, 2012, 06:15:51 pm
Hi all,

I was wondering how you are planning your projects. I usually go the same way I did when I was playing Legos... I think, do, rethink and redo and so on until I get it right making up new things as I go along.
This works for small or not so complicated projects but I would like to know about a method that would work with bigger and more complex projects.
So, how do you go from a vague idea to a prototype and a final design? Maybe I wasn't googling the right words but I couldn't find any good howto on the matter.

Thanks!
37  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 19, 2012, 07:11:23 am
It turns out it was bad grounding. I fixed it and it seems to be fine for now. Thanks all!
38  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 02:39:55 pm
What are you using as your ground when measuring the voltage coming from the switch? If a wire comes to the switch, another leaves the switch and goes to the bulb and the bulb is grounded then you should have 12V at the switch. If you don't have 12V at the switch then you need to check fuses and/or damaged wiring.

When you get an odd voltage reading on a device that was once working then you have something that failed and the best fix is to find out what failed and replace it. Not hook up some device you pulled out of your imagination to fix a problem you have not troubleshot.

The problem in this case is that for some reason you are not getting 12V to a device that should have 12V to work. The problem is not that you have .95V and you need it to be 12V.

I am using a voltmeter on the two connectors coming to the light bulb. I checked the fuses in the fuse box and they are all fine.
39  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 02:37:50 pm
In most older car designs the boot switch is actually a grounding device.  ie the lamp is permanently supplied with a 12 volt line and the other side of the lamp then runs to the boot switch.  When the boot is opened the switch actually takes this line down to the chassis of the car, so completing the circuit to the lamp. ie a "grounding " switch

So the first question you need to answer is  " Does the switch have 1 or 2 terminals"   

If only 1 then you have a "grounding" switch. If so then I suggest that there are at least 5 possible options

a) the 12 volts line to the lamp is defective
b) the lamp holder connections are corroded
c) the lamp is dead
d) the wire from the lamp to the switch is defective
e) the switch is defective (possibly just corroded)

You have not advised the model or age of the car  --all information that might get you an informative answer

The car is a Toyota Avensis T22 from 2002. I cannot check the resistance or anything of the switch because it is not easily accessible. It is burried under the trunk latch...
40  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 12:16:13 pm
A few questions...

Do you know where that "12V" wire is coming from?   For example, is it "power" from a switch or something, or is it some sort of low-current "control signal" ?   If you don't know what the wire is for, you shouldn't be connecting things to it...  or at least you shouldn't be connecting anything that draws more than a fraction of a milliamp.   

What's normally connected?    The light is something you're adding, right?

Do you get 12V without the light connected?   I mean, what makes you think there should be 12V there?  Ort, did you connect the light and blow something, so that there's no longer any voltage there?


I was a bit evasive in my OP, sorry about that.

The light in the boot of the car is not coming on anymore when the boot is open.
I checked if the lamp was fried but it's not.
Then I checked if the switch to detect whether the boot was opened or closed was working, and it is: when the switch is pressed (= boot closed), there is 0.00V flowing to the lamp. When the switch is not pressed (= boot open), there is 0.95V flowing through. But the lamp is not coming on because it is rated for 12V 5W.

So I thought I could just use a voltage regulator to take the voltage back up to 12V and have the light work normally. Or I could make a small PCB with a 3.3V regulator, a resistor, one or two 12k mcd white LEDs and a fuse (the original Toyota lamp looks like a fuse and I'm thinking it doubles up as a fuse) and place it there so I could get light with minimal voltage and current draw.

Alternatively, I could use a ATtiny to monitor the wire for voltage and turn on the above mentionned LEDs PCB powered by a battery or two that I would change every now and then.

My main problematic is that I have very basic electronics knowledge and I don't have the tools not the courage required to take the car apart to dig up the wire and check it all the way to the (brand new) battery.

All in all it's a minor annoyance, everything else in the car is working fine, but I thought it could be a useful and fun mini-project. Thoughts?
41  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 11:40:08 am
I see. Could there be an easier way to check for damage than pulling the wire out? I have no idea where it's running and I don't want to take the car apart. Or maybe I should put one or two LEDs instead of the 12V lightbulb? They won't draw too many mA and they will be happy with 1V?
42  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 08:44:09 am
I'd go try to figure out why the wire produces 0.95V.  Otherwise it sounds like you're playing with fire here...

You reckon I could damage something?
43  Using Arduino / General Electronics / Re: Raising 0.95V to 12V? on: April 18, 2012, 08:41:04 am
I must add the battery is fine and everything else in the car is working fine, other lights etc are getting a steady 12V.
44  Using Arduino / General Electronics / Raising 0.95V to 12V? on: April 18, 2012, 08:36:24 am
Hello,

I'm sure this is the dumbest question ever: I have 0.95V on a wire and I need to raise it to 12V to turn on a light in my car. For some reason the wires don't supply 12V anymore but only 0.95V. How should I go about this?

Thanks,
45  Using Arduino / Project Guidance / How to safely use 220V relays? on: April 16, 2012, 07:04:35 am
Hi all,

I bought these 220V relays working off 12V recently and I'd like to hook them up to the 220V mains to do interesting things.
However, I am very concerned about electrical safety? What is the best practice to avoid electrical shock when prototyping? I was thinking about making custom PCBs to solder the relays on and screw the main wires into those little screw connectors (if you see what I mean) but that still leaves some live 220V wire exposed.

How do you deal with this particular issue? Also, should I fuse anything? I have lived in the UK in the past and I know plugs have 10A fuses inside them there but is it really necessary?

Thanks!
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