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1  Using Arduino / Sensors / Re: What would temperature sensor do with wrong resistance? on: June 05, 2011, 02:42:03 pm
Interesting.  I've read a few other reports about this, seems others believe this sensor can give readings that are too high.  Not too worry, I shall see if I can buy a good scientific thermometer to compare readings and calibrate with.

P.S. Thanks for moving this mellis.
2  Using Arduino / Sensors / Re: What would temperature sensor do with wrong resistance? on: June 04, 2011, 08:02:36 am
Just realised I've posted this in the wrong section, could someone move it please?
3  Using Arduino / Sensors / What would temperature sensor do with wrong resistance? on: June 04, 2011, 07:37:29 am
Hi guys,

I've set up a temperature monitoring device using the One Wire Digital Temperature Sensor (DS18B20).

Now this setup requires a 4.7K pull-up resister however the only 4.7K resister I had wouldn't work (blown, fried, what ever resisters do when they die).  So I grabbed the only other resister I could find at the time, a 10K one.

Now the device I've made is working fine, (view its current reading at www.andybarratt.co.uk/temperature) but I'm finding it's readings to be a little too high.

Could someone tell me if this is being caused by the resister?

Datasheet for the sensor is here http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=36_68&products_id=585

Thanks,
Andy
4  Using Arduino / General Electronics / Re: Some kind of electronic switch on: April 08, 2011, 11:59:26 am
Thanks, that looks really useful.

I'll try my best to explain, though I have a habit of rambling so forgive me if I confuse you.

I have a model airplane with four servos for various controls.  For this I'll just talk about one of them, the one that controls the ailerons (bits on the wings that wiggle to make it roll left and right).

This servo is connected to a radio control unit already which gives me my full manual control.  Here's where I start to have my fun, I have an arduino with a bluetooth adaptor that speaks to an android phone that it placed inside the plane.  The phone has all the sensors and internet access I need to develop some pretty cool stuff, eventually to the point that the plane will fly itself.

Right now the plane is set up so that when it tilts, the phone detects this and the arduino uses the servo library methods to compensate.

Now here's my problem, I can not in all good conscience allow Hera (the plane's name) to fly without having the fail safe of taking back manual control if the the phone dies.

What I can do is connect both circuits to the same servo with the ground to the radio control unit and the arduino being tied in together.

The arduino's signals from the servo library methods seem to be powerful enough to drown out all signals coming from the radio control unit.  I'd thought that sending the:
ailerons.detatch();
command (from the servo library) would be enough to give me back control but apparently not.

The only method is to disconnect one of the wires that completes the circuit between the arduino and the servo, either the signal or the ground, this breaks the circuit with the arduino and gives back all control to the radio control unit.

Now I had thought of putting this electronic switch on the signal pin but I figured that considering I will eventually be having all four servos connected up, I may as well put it on the ground because after all, that would mean just one wire to be playing with, rather than four.

I hope I've made sense enough for you to picture what I'm doing, if you've better ideas for solving this, please tell, as I said, I'm no electronics expert smiley
5  Using Arduino / General Electronics / Some kind of electronic switch on: April 08, 2011, 11:02:22 am
Hey guys,

I'm not sure if this is an unusual one or not but it's the situation i've found myself in.

I need to be able to switch a ground wire on and off on demand.  After testing, I know this is the best course of action for what I'm doing and I can see on my bread board that unplugging the ground gives me one function I'm needing and plugging it back in gives me a different function I'm wanting.

What I'm really needing is some kind of switch that when I send a:
digitalWrite(switchPin, HIGH);
it'll complete the circuit leading to the ground pin and when I send a:
digitalWrite(switchPin, LOW);
it'll break the circuit.

I'd thought I could do this with a transistor but so far have had no luck, though it is entirely possible that I'm not doing it correctly, I'm afraid I'm no expert of electronics.

Can anyone help me out here?  I'm sure it must be very simple really.

Andy
6  Using Arduino / Project Guidance / Re: UAV - Gyro, Accelerometer or both? on: March 17, 2011, 06:35:18 pm
Wow, what a brilliant article, thanks.  That's going to be really useful.  I'll post a link to the code I come up with, thanks smiley

Andy
7  Using Arduino / Project Guidance / Re: UAV - Gyro, Accelerometer or both? on: March 16, 2011, 03:53:54 pm
Thanks.

Congrats on 500 posts by the way smiley

Anyone able to share knowledge of accelerometers in air craft re: what i mentioned about it not doing well with free fall and if this is going to be an issue?

Andy
8  Using Arduino / Project Guidance / Re: UAV - Gyro, Accelerometer or both? on: March 16, 2011, 03:41:08 pm
Cool, that's what I'll do then.

Though, I'm still confused as to how I'll actually let the system know which way it's facing.  I could hold the entire system very still, as if it's nose diving at a scary angle and it wouldn't know because it's not actually rotating.

So does this mean I will definitely need something like an accelerometer?
9  Using Arduino / Project Guidance / Re: UAV - Gyro, Accelerometer or both? on: March 16, 2011, 03:24:29 pm
Aha, so if I get myself a three axis accelerometer then I can work out if I'm horizontal?

I'd assumed that even with three axis, no matter what direction the bottom of the plane is facing, if it's not rolling in any direction then it'd just read out as zero.

As it happens, I do have two dual axis gyros.  So if I combine these, will I be able to code something that'll know which way up we are?

Both gyros work on X and Z (roll and yaw) though obviously, with some sneaky rotation, I can make one of those Xs a Y (such cunning).

Andy
10  Using Arduino / Project Guidance / Re: Connecting Batteries Directly To Arduino Pins on: March 16, 2011, 02:41:30 pm
You could solder the battery pack to the barrel connector so you're using the voltage reg on the board.

lol, came to this post with curiosity at what might get thought up.  Love how simple this solution is... now do I dare trust my soldering skills near my Arduino smiley-lol
11  Using Arduino / Project Guidance / UAV - Gyro, Accelerometer or both? on: March 16, 2011, 02:36:12 pm
Hello,

I've got a model air craft and right now I'm just trying to get something real basic sorted.

When the airplane starts to roll left or right, sort it.  When we start to pitch up or down (climb/nose dive), sort it.  Effectively, just something that'll keep it all level.

Here's my question, should I use an accelerometer or a gyro to do this?

Accelerometer seems like an obvious answer to me, as it knows which way is down, but I'm led to understand that this would not work very well on a plane (i.e. when in free fall, it reads 0).  Is this the case or am I misunderstanding?

At the moment, I've got a gyro on it.  But this will only tell me when the plane is rolling and when it's not.  It won't actually tell me when the plane is horizontal.

So what's my solution?  Am I wrong about the accelerometer, that it won't work in flight (please tell me I'm wrong) or perhaps there's some solution that incorporates both, i saw a few things that had both built into them but I've no idea what for :-S

Looking forward to your replies smiley
Andy

p.s.  Here's a link to the project blog http://blog.andybarratt.co.uk/?category_name=project-hera
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