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1  Using Arduino / General Electronics / Re: 24v to 5v power issues, again. on: April 10, 2014, 03:55:19 pm
I was just going to ask about where the diode was connecting to...

I'm not familiar with that specific regulator.  I am much more used to working with much smaller components.

You're not going to need anywhere near the amount of power that regulator can provide, that's for sure.  You're not using it to power external things, just interface with them, yes?

I'm more used to using things like the MCP16312 which is a tiny SMD device, and takes a few equally small SMD devices.  Here's a typical layout with one I am working on for a project (regulator is U2, input is top, output is bottom):

So, I'd say, to reduce the size of the components, pick a regulator that works with smaller components.
2  Using Arduino / General Electronics / Re: 24v to 5v power issues, again. on: April 10, 2014, 03:31:56 pm
I think you put a wrong link in there - I see no document.

Switching regulators and breadboards don't mix too well.  The datasheet should give a recommended PCB layout to keep everything in specifications.
3  Using Arduino / General Electronics / Re: Is capacitive sensing possible with batteries? on: April 10, 2014, 01:48:36 pm
By the way, you're confusing "ground" and "earth".  "Earth" is the thing you are standing on. "Ground" is the point in your circuit against which all other voltages in your circuit are measured.  It has absolutely nothing whatsoever to do with what you are standing on.

OK, semantics aside....

I want a Tiny85 based device under the lid of a jam jar. I want it to turn on some LEDs when I touch the lid. It's powered by a coin cell.

How can I do that?



By charging two plates with a constant current for a predefined time, then measure the voltage across them.  Your finger, or the air if there is no finger, is the dielectric that affects the capacitance, and hence the final voltage, of the plates.  It's up to you how you arrange the plates to achieve the best effect.

Here's one possible design:
4  Using Arduino / Programming Questions / Re: Serial.Find Problem on: April 10, 2014, 01:33:34 pm
By the way, there is a default timeout of 1000ms on the .find() function.

So you're basically saying:

Wait until I see the string "SOMETHING", or for a maxium of 1 second, whichever is first.
Did I see the string?  No?  Ok, wait for the string "SOMETHINGELSE", or for a maximum of 1 second, whichever is first.

It will only ever see "SOMETHINGELSE" and react to it if it arrives in the second 1000ms after the first .find() for "SOMETHING" has timed out.

You need to read the whole string in and then look at it to see what is in it and compare it to different things to find out what it matches.

Imagine living on a 1-way street of houses numbered 1 to 100, and you live at number 1.  You get in the car and "Drive until you reach house number 186, or you reach the end of the road.  If you reached the end of the road then keep driving until you reach house number 50, or until you run out of petrol".  You're going to run out of petrol, because you drove straight past house number 50 while looking for the non-existent house number 186.

Now, if you had instead gone: "Ok, I need to get to house number 186 - oh, the street doesn't have a house 186, OK, I'll go to house 50 instead." it would have been better.
5  Using Arduino / General Electronics / Re: Is capacitive sensing possible with batteries? on: April 10, 2014, 01:25:10 pm
By the way, you're confusing "ground" and "earth".  "Earth" is the thing you are standing on. "Ground" is the point in your circuit against which all other voltages in your circuit are measured.  It has absolutely nothing whatsoever to do with what you are standing on.
6  Using Arduino / General Electronics / Re: Is capacitive sensing possible with batteries? on: April 10, 2014, 01:22:30 pm
Capacitative sensing relies on you changing the capacitance (by changing the dielectric value) between two plates.  One of those plates is an analogue input, and the other is ground.  Yes, it is possible (though wrong) to use the earth as the ground plate, but you should really have two plates on your PCB layout, and you measure the capacitance between them.

It sounds like you're doing it the lazy way and only having one plate in your design and relying on the ground being the other.
7  Using Arduino / Programming Questions / Re: Serial.Find Problem on: April 10, 2014, 01:22:19 pm
It won't be checked, no.  It'll wait until it finds the first one, and never get to the second one.

You'll have to check the data manually as it comes in.
8  Using Arduino / Programming Questions / Re: negative value Conversion. on: April 10, 2014, 06:19:43 am
au16data is unsigned - how can it hold a negative value?

Instead of working with negative angles, why not work with positive values?  Remember, angles are in a circle, so -1° is the same as 359°, -2° is 358°, etc.
9  Using Arduino / General Electronics / Re: Powering Arduino from 12v 1A linear regulator? on: April 09, 2014, 09:19:57 am
I think that's mainly to cover their backs.  There's no real technical reason not to do it, but numptys could connect what they think is 5V only to find it's unregulated and actually much higher.

It's perfectly safe to apply a properly regulated 5V supply to the 5V pin.  You might like to add a diode between 5V and Vin (anode to 5V, cathode to Vin) to allow any reverse voltage to safely bypass the onboard 5V regulator, just to protect it from damage in case you should apply any load to Vin.
10  Using Arduino / General Electronics / Re: arduino as ammeter on: April 09, 2014, 05:43:51 am
For example (just an idea, needs fine tuning may be). The op-amp type is just an example.
Arduino is isolated from the power lines by a separate battery. Do not connect Arduino GND and power GND together !
Or, keep it simple, and use the AD8215 like I suggested on the last page - that way the Arduino can share the power supply (with suitable regulation of course), ground, etc, and it's just one chip and a capacitor or two (decoupling).
11  Using Arduino / General Electronics / Re: Powering Arduino from 12v 1A linear regulator? on: April 09, 2014, 05:18:56 am
Quote
Connecting a few of the regulators in parallel allows a few more outputs to work before they all cut out.
Connecting regulators in parallel is bad. Don't do it.
You see, you have to remember that voltage regulators are active devices.  That is, they watch what is going on with the voltage and make a decision about what to do with it.  If the voltage drops too low it makes the decision to increase its output to raise the voltage.  If it's too high, then it decides to lower its output to compensate.  Now imagine you have two regulators in parallel.  They're both going to be making independent decisions about the same voltage.  They'll both decide to raise their voltages or lower their voltages, and the net result will be too much or too little voltage all the time, so they'll then try and compensate again.  The two regulators will be fighting against each other to gain control of the voltage, and neither will get control.  They'll just be getting in a complete mess.

Connect an oscilloscope up to one of the paralleled regulators, and chances are you'll see the voltage varying massively all the time.

The way to increase the power handling of a linear regulator is to add an external PNP power transistor, but I wouldn't recommend it, since the way to go is definitely with a switching regulator.
12  Using Arduino / General Electronics / Re: Powering Arduino from 12v 1A linear regulator? on: April 09, 2014, 04:10:51 am
Well, yes, it's a linear regulator, and you're dropping 50% of the power as heat.  It's bound to get hot.

You will need a "Big Ass™" heat sink on it, or better still, replace it with a switching (buck) regulator.
13  Using Arduino / General Electronics / Re: arduino as ammeter on: April 09, 2014, 04:08:28 am
Of course, no one has thought to ask the most obvious question...

Why the hell have you got such a stupidly powerful stereo in your truck...?!
14  Using Arduino / General Electronics / Re: arduino as ammeter on: April 08, 2014, 10:16:16 am
Sounds like you're going to be needing to do high-side readings for that kind of rig.  You want to look at the AD8215 and similar chips.
15  Using Arduino / General Electronics / Re: arduino as ammeter on: April 07, 2014, 01:58:33 pm
The thing with a shunt, it's basically a low-ohmage, high accuracy, resistor.

To know if it will "work" with the Arduino, in that you can a) read decent values from it and b) not fry the Arduino, you need to do a bit of Ohm's law.

You need to know the resistance of the shunt, and you know the expected peak current.  Given an example resistance of 0.001Ω (1mΩ), we can calculate that for 200A flowing through it you will drop (V=R*I) 0.001 * 200 = 0.2V.  That's not much range to play with.  If the shunt is 0.01Ω, however, that would equate to 2V.  If it were 0.1Ω it would be 20V and your Arduino would melt.

Also, if you're thinking of doing high-side readings, you'll need a high-side current shunt amplifier to isolate the higher voltage offsets from the arduino.  Do low-side if you can.
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