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1  Using Arduino / General Electronics / Re: How do I calculate the values for an LC or PI filter? on: Today at 02:12:38 am
One approach you have not attempted yet is to lower the input impedance of your amplifier to reduce the pickup of the noise.
I would use the transformer and load the output side with something like a 4K7 resistor going into your amplifier.
2  Using Arduino / Audio / Re: MAX7219/7221 and DAC noise on: Today at 02:04:32 am
It is hard to recommend anything without seeing a schematic and a photo of your layout. Normally bigger large capacitors and a star ground should work providing of course, your power supply can cope with the current draw you are asking of it.
3  Using Arduino / Audio / Re: Reading MIDI, converting to polyphonic square wave with Tone library on: Today at 02:01:34 am
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When I said PWM that's not used by analogWrite, I meant that I need to be able to vary the frequency
If the frequency changes then it is not PWM, it is as simple as that.

Yes you can use external resistors to mix outputs, that is no problem.

As to indexing you have an array with an entry for each tone you are producing. In the note on function you search for a free channel and mark that as being in use by setting that array element to the note number. Then start that oscillator playing.
When you get a note off message you search the array for that note number, when you find it you stop the note and clear the note number, thus indicating it is a free for use again.
4  Using Arduino / Audio / Re: MAX7219/7221 and DAC noise on: Today at 01:50:25 am
There is nothing that seprate supplies will not do that can not be done by adequate decoupling. If a soloution did not work then it didn't go far enough.
5  Using Arduino / Audio / Re: MAX7219/7221 and DAC noise on: July 27, 2014, 04:33:35 pm
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Not sure why that works the way it does
This is because you had a total lack of power supply decoupling originally.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
6  Using Arduino / Audio / Re: Reading MIDI, converting to polyphonic square wave with Tone library on: July 27, 2014, 04:31:33 pm
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I will need to use PWM (and when I say PWM I mean actual pulse width modulation, not just what's used for analogWrite() ).
So why is PWM not what is produced by analogWrite?

You will here no difference in frequency when you alter the duty cycle.
You have to decide how many channels of polyphony you want and code accordingly. You could use an interrupt driven phase accumulation pointer to derive the frequencies but if you just have a digital output there is no way to mix several tones on one pin.
7  Using Arduino / General Electronics / Re: voltage prescaler question. on: July 27, 2014, 04:19:37 pm
OK make sure your switch is a "break before make" type and not a "make before break".
8  Community / Local Groups / Re: Boston, Lincs, UK i.e. the original ? on: July 27, 2014, 04:17:34 pm
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and seeing one of the palaces (also in Windsor?).
Apparently Americans ask why they built Windsor Castle so close to the airport.

I was in the Lake District in England (where I also live part of the time). I wan in the pub next to Beatrix Potter's house an a  American walker who was traumatized by a Taxi ride. She complained that he went so fast so close to solid stone walls.
9  Using Arduino / General Electronics / Re: Digital Ground/Analog Ground, Arduino Gets Stuck! on: July 27, 2014, 03:51:38 pm
i tried connecting the dc motors with 0.1 microfarads capacitor. but to no avail. should i add the capacitor to 5volt and ground on L298N driver shield?
The thing about decoupling is that you have to increase what you do if it is insufficient. Yes you should add capacitors to the supply of all the devices you have both a 0.1uF and a big one like 47uF to 10,000uF. You should even consider the pi filter like on the last page I showed. As a temporary measure you can try running your motor off a separate supply, if this works then you know you have to keep going with improving the decoupling and layout.

Have you checked with your meter that your power supply is holding up, that is the voltage is not dropping as you draw more current?
10  Using Arduino / Project Guidance / Re: Any way to add SRAM to Arduino? on: July 27, 2014, 03:44:35 pm
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Could it be setup to run like an Arduino?
No not really. There is Bare Metal, that has no OS:-
http://www.valvers.com/embedded-linux/raspberry-pi/step01-bare-metal-programming-in-cpt1

But better that that there is RISC OS. This is the desktop operating system that all the others stole ideas from. It is a cooperative multitasking system, unlike Linux which is preemptive. It runs a blisteringly fast version of BBC Basic. Just printing a numbered line it goes at about 290 lines per second as opposed to Python under Linux which runs at 6 lines a second. And within a Basic program you can drop into machine code when you want things to really fly.
 Extremely responsive desktop where windows can actually be dragged behind other windows, minimised, maximised, dragged off screen or scaled to the size you require.
https://www.riscosopen.org/wiki/documentation/show/Welcome%20to%20RISC%20OS%20Pi
11  Using Arduino / Microcontrollers / Re: Intel Galileo has integrated linux OS on: July 27, 2014, 05:13:54 am
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Yep. Makes me wonder what use it is. What are the people at Intel thinking?
They were thinking that they had to get something out for the launch at the Rome Maker Fair last year. I was talking to the design team and they only had one shot at the CAD and did the whole thing including getting it into mass production is less than 60 days.
You can run it without knowing there is Linux on it only then it will not remember the previous sketch. The design team did not know that the I2C chip that handled the I/O could not run at anything other than the default 100KHz rate and to be fair it is hidden in a rather obscure part of the data sheet. They were expecting it could run at 1MHz so the stupidly slow I/O would just be slow.

There are advantages however in the PC like buses on the processor. Basically the arduino bit is emulated from a much faster processor, so it is much faster than the Due in doing actual calculations and it has tons of memory. However for the sorts of projects I do I need fast access into and out of that memory.

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I guess they're relying on the "Intel" name to sell it to American corporations/educational institutions.
No, it is not a product in the normal Intel sense of the word. It came about because the new CEO of Intel was at a presentation from someone prototyping something with an Arduino. He offered this person special prices on the processor if he would switch to an Intel one, he refused. Then the offer was for millions off prices, then at cost price, and then for free. The person wanted to stick with the Arduino because of the "support community" around it. The CEO wanted "in to this" hence the Galileo which he described as "just the first in a series of like offerings".

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As a hobbyist it doesn't seem to offer much compared to (eg.) a Raspberry Pi at half the price.
I got mine for free at the Maker Fair, they had 400 they were handing out. I think I payed too much for it.  smiley

 
12  Using Arduino / General Electronics / Re: I connect LED 12V 1W to arduino but LED few bright. on: July 27, 2014, 04:28:44 am
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How to create low power circuit for drive LED 12V1W with arduio.
I have no idea what you mean because a load of 1W is not low power.

How many LEDs do you want to light up? What are these LEDs, specifically do you know their forward voltage drop?

Do not connect raw LEDs in parallel they will not share current.
13  Using Arduino / General Electronics / Re: PWM, Low Pass Filter, Transistor, & P Channel MOSFET on: July 27, 2014, 04:25:00 am
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This page calls it a transistor based voltage divider. Is that the same thing?
I don't know because the page would not let me see anything. I have never come across it being called that but it could make sense.

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If it is current controlled then how do you know when it is saturated?
It is saturated when an increase in base current produces no increase in collector current.

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For instance if I had a load on transistor that took 100mA, but my base current and gain were such that only 50mA were allowed to flow I am assuming that would not be saturated.
Correct.

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But does 100mA constitute saturated, or 150 or 200mA? Like at what point is it saturated?
When a transistor is saturated there is a fixed voltage between emitter & collector, this is normally 0.7V although at high currents this can increase, in the data sheet this is called Vsat. We say the transistor is "Hard on" in other words the rheostat is turned down as much as it will go.

So the saturation current for any circuit is the voltage across the load resistor over (divided by ) the resistance of the load resistor. The voltage across the load resistor is the supply voltage minus the Vsat voltage.

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Like in an op amp or something?
Yes  smiley
In fact transistors were around first and op amp feedback used to be described as "like the emitter resistor".

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So the less the base current the more the resistance?
Yes.

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Does the higher impedance (then lower) impedance have an advantage?
The bigger a capacitor is the more expensive it is (in general ) so it is better to have a high resistor and a small capacitor. However such a high impedance will not drive very much, so in a simple RC filter you have to have the impedance low enough to drive the load. The transistor converts the impedance so you can have a low impedance output to drive a load.
14  Using Arduino / General Electronics / Re: PWM, Low Pass Filter, Transistor, & P Channel MOSFET on: July 27, 2014, 01:44:43 am
So like an automated guitar with harpsichord kind of sound, that's pretty neat.
Well it is MIDI so it can sound like however you want. But I wanted it to have a finger picking acoustic guitar playing style instead of the distorted power chords you get in a lot of 'Keytars' as they are called.
 
I did it back in 2009.
I can even play "House of the rising sun" on it. But as you heard from my "Post your Code" efforts, my voice isn't the greatest  smiley
15  Using Arduino / General Electronics / Re: PWM, Low Pass Filter, Transistor, & P Channel MOSFET on: July 27, 2014, 01:40:48 am
Interestingly enough however there appears to be a voltage drop across the collector and emitter of the transistor though. Is that normal.
Yes it is. That is how the circuit works.
Most circuits here have the emitter connected straight to ground because the transistor is being used as a switch. To do this you need the transistor saturated, that is as hard on as it can go.

In this circuit the transistor is acting as a linear amplifier. The resistor in the emitter acts as a negative feedback mechanism reducing the gain of the transistor to allow the change in the voltage, applied to the base resistor, to be reflected in the change in voltage on the collector. This allows the FET to be driven in the linear region and give you the proportional control you are looking for. Any restriction of the current in the collector circuit shows up in an increase of voltage across the collector / emitter. That is how transistors work. Think of them as a current controlled (base current) rheostat, with the collector / emitter representing the rheostat. (Yes I know it is not quite like this but in terms of thinking about the circuit it is practically the same)

The PWM filter is on the base side of the circuit allowing you to use higher impedances in the RC filter (bigger R smaller C), then the transistor reduces that impedance and also amplifies it to to the 12V range you need for controlling the FET. I found you need about 34% PWM to start the motor moving.
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