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1  Using Arduino / Audio / Re: Record and playback audio, also via ethernet. on: October 10, 2013, 07:45:13 pm
I would be interested if I had the time. I put Arduino aside for a while.
2  Using Arduino / Project Guidance / Re: Controlling a low value resistance to ground on: October 04, 2013, 11:36:59 pm
The filter and a lifted base voltage for the transistor only requires resistors and a capacitor.
If you have a value of 225 for analogWrite(), the value of the resistors should be altered.

You should be very careful with that 2000V.
It could bounce back and destroy the Arduino and PC (connected via usb).
Two single blocks is better.

You can't set the transistor to a certain 'resistance'. It doesn't work that way. It can be set for a certain current through the collector, which can result in this circuit like a resistor.

When you use the circuit for a while, there will be some dust, or moisture or other things. That is a real danger with 2000V. You should use a large distance between the blocks, not just barely outside the spark range, but a lot more.
3  Using Arduino / General Electronics / Re: writeMicroseconds() reduced voltage? on: October 03, 2013, 12:08:02 pm
The voltage divider is the most easy way.
It's ten times easier than the other options: a level converter board or a level converter chip or a mosfet or logic gate.

So the 5V power to the servo is not from the 5V pin of the Arduino. That's a relief.

If you have it working and want to make it small, the Pro Mini for example is very small. The Pro Mini doesn't even have a usb connector, so you have to buy an extra board to be able to upload a sketch.
4  Using Arduino / Sensors / Re: Problems with arduino mega 2560 and MPU 9150 on: October 01, 2013, 02:57:59 pm
The range of the accelerometer is set with the AFS_SEL bits in a config register I think.

I know nothing about that magnetometer, so I can't help you with that.
However, when looking at the graphs, it looks typically like a software problem with a wrong higher bit conversion. At least I can guarantee you that it is not a saturation problem.
Perhaps an offset has to be set, or the conversion from the 13-bits is wrong. What do you do with the unused 3 bits ?

When the sensor is near your computer or near a monitor, it measures the magnetic field from that device, rather than the (tiny) field of the eatch magnetic field.
5  Using Arduino / General Electronics / Re: writeMicroseconds() reduced voltage? on: October 01, 2013, 02:37:51 pm
I can't find any specification for the current. Using the 5V pin of the Arduino to power a servo is normally a bad idea. Could you measure the maximum current when blocking the rotation of the servo ?

The lightweight low-voltage servos work at 2.8 to 4.2V. That means it is designed to be powered by a single Li-ion or Lipo cell.
Also a Arduino (compatible or standalone) can be made to work at those voltage.
6  Using Arduino / General Electronics / Re: Ambient radio wave energy on: September 30, 2013, 04:22:49 am
Do you know an energy harvesting ic that collects energy from radio waves ?
I can only find ics that use motion, or peltier, or solar, or nearby inductance, and so on.
7  Using Arduino / General Electronics / Re: writeMicroseconds() reduced voltage? on: September 30, 2013, 04:17:32 am
roineust, sorry, my fault. I mentioned a 4k7 as protection resistor, but AWOL corrected me and wrote about a voltage divider.

Like here.
http://learning.codasign.com/index.php?title=Light_Dependent_Resistors_and_Arduino
Vin = from the output pin of the Arduino.
Vout = to the servo signal (white) wire.

With the diodes you power the servo motors with about 4V.

To convert the 5V signal to 4V, you need a voltage divider that is Vout = 4/5 Vin.
For example R1 is 2k2 and R2 = 10k
Or R1 = 1k and R2 = 4k7

With the voltage divider the servo gets the right signal voltage, and the resistors also protect against too much current (for both Arduino and servo) if something would be wrong.


Do you know the maximum current of those lightweight servo motors ?
8  Using Arduino / Project Guidance / Re: Controlling a low value resistance to ground on: September 29, 2013, 01:51:13 pm
I was not clear what I ment, sorry. I ment this: "Set the potentionmeter to the highest value of the high voltage, and see if you can achieve the same with the Arduino".

The transistor might be damaged. You need at least a resistor from the Arduino pin to its base.
To control the transistor you can use a PWM signal, but you have to filter that with a resistor and a capacitor.
Without filter you have a combination of the PWM frequency and the 555 frequency, that would result in heavy interference.
9  Using Arduino / General Electronics / Re: Ambient radio wave energy on: September 29, 2013, 12:48:06 pm
My idea (LW and MW waves) is totally different from catching energy from GHz signals.
Flashing a led with a mobile phone is only for a very short distance.
It is hard to say which signal is strong enough.
A good quality spectrum analyzer will show what is in the air.

Do we agree ? That getting energy from all frequencies at the same time is very hard ? And by tuning to a frequency you have to know about a strong signal.
10  Using Arduino / Project Guidance / Re: Controlling a low value resistance to ground on: September 29, 2013, 12:33:36 pm
For full control, you might need a different circuit.

The coil/inductance together with the capacitance of the circuit has a certain optimal frequency. You could try to find that frequency and use the Arduino to regulate the voltage with a lower frequency.
The frequency changes with an other load (other tube), but perhaps you can find some average optimal frequency.
That might be between 100kHz and 1MHz. Perhaps you have to write your own code for the registers of a timer.

Do 1 Gohm resistors exist ?
I doubt if that is useful.
A value of 100M can be used, but even that is very high and therefor not accurate.
Sensing 3000V with 100M will lower the high voltage.

Using a transistor or mosfet is something worth trying. What kind of problem did you encounter ? The lowest value was 30 ohms ?
That doesn't seem right. You can't measure that with a multimeter. Set the potentionmeter to the highest value and see if you can achieve the same with the Arduino.

Can you draw a schematic ?

You could do the tests without cascade, that high voltage scares me.
11  Using Arduino / General Electronics / Re: Ambient radio wave energy on: September 29, 2013, 10:04:53 am
The capacitors are a problem: they leak.
Blinking a led requires more energy than audio in a piezo (crystal) earphone.
The led has to blink long enough to be visible, that would be about 100ms. The 1mA during 100ms needs a lot of energy.

Powering an LCD clock would be easier. Even a larger LCD display requires almost no current.

There is a problem with radio waves: If you use only a coil, you get a lot of everything, but the result is almost nothing.
However, if you tune in to a strong radio station, you can get energy out of that.
Try to make an antenna, like a circular coil of 1 meter (or 1 yard) diameter. About 50 to 500 windings. Don't use very thin copper wire, that reduces the current. Add a variable capacitor and a radio diode. The diode to a capacitor and see if you can charge the capacitor when tuning to find a radio station.
12  Using Arduino / Project Guidance / Re: Controlling a low value resistance to ground on: September 29, 2013, 09:50:20 am
You picked the wrong circuit to do this.
Is the Arduino going to measure the high voltage ? or do you just want to set the potentionmeter ?
I don't think that circuit can do 2000V.
The transistor is 400V and the diode is 1000V and the capacitors are 1000V.

I would use the Arduino to generate the frequency for the high voltage, but a 555 chip is used. That make it harder to control.

The 100 ohm potentiometer is part of the circuit. If you replace it with a transistor, it might not keep the high voltage at the same voltage.

What are your goals ? What are the voltages you want ?
Do you have to use this circuit ?

My best advice is to use a few relays and a few potentiometers, and let the Arduino select the relay for a certain voltage.


13  Using Arduino / General Electronics / Re: writeMicroseconds() reduced voltage? on: September 29, 2013, 05:37:28 am
The Arduino 5V pin is not for servo motors.
Normal standard servo motors (4.8 to 6V) could require a start current of 500mA or more. That is too much for the Arduino.

You solution with 2 diodes might work or not. You should measure the voltage as the servo is not active and also with full power. But the servo current is still supplied by the Arduino.

The voltage of the output pin can not be changed.

I can think of few solutions.
  • Use normal servo motors, and power them with a seperate power supply (or a seperate voltage regulator or DC-DC converter)
  • Use a 3.3V Arduino board. You still have to make a power supply for the servo motors.
  • Use a 5V Arduino board with your servo motors. Read the datasheet of the servo motors, perhaps the inputs are 5V tolerant or a series resistor of 4k7 in the signal line will work. Perhaps you need level shifters. You have to take a good look at the current that the servos need, you probably need a seperate power for the servos.
14  Using Arduino / Motors, Mechanics, and Power / Re: Drive a 60 W Peltier with Arduino on: September 28, 2013, 05:25:31 am
Heating without overshoot ? What about a simple heater ?
Perhaps a PID to prevent overshoot.

A PSU from a PC can be used.
Some old ones requires a small load, so you have to check the output voltages without load.
There is a sense wire, and you have to connect it to something.
http://reprap.org/wiki/PCPowerSupply

I have such a prepared PSU and it's very handy to have.
15  Using Arduino / Microcontrollers / Re: Is avrfuses still necessary with Arduino 1.0.5 on: September 27, 2013, 04:46:20 am
Yes, with avrdude.
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