# Tag Info

30

That looks like a sine wave with the y-axis wrapped around. Here's my attempt at recreating it: This is a plot of the function $1.25 \cdot \sin(t) - \operatorname{round}(1.25 \cdot \sin(t))$, where $\operatorname{round}(x)$ rounds $x$ to the nearest integer. Perhaps the highest bit of your signal is getting cut off? That would seem likely to ...

18

First, some microcontrollers DO have D/A converters. However, these are far less common than A/D converters. Aside from the technical issues, the main reason is market demand. Think about it. What kind of application would require a real D/A? It is quite rare to want a micro to produce a reasonably high speed analog signal unless the point is signal ...

17

What you have right there is what is known in the field as an R-2R DAC, one of the many different kinds of often employed digital-to-analog converter topologies. You have answered your own question: why do we need DACs when we have this DAC topology? Because it is a DAC! R-2R DACs purely by themselves are not great as a general purpose digital to analog ...

16

What is your required precision/accuracy? I will cover the foundations of a simple method, and update if necessary. Parts: You may already have what is necessary ;) Lets look at your PWM outputs. Depending on the duty cycle, or how long the pulse is "high" compared to "low", an average level can be achieved. You can keep this chart in mind as you are ...

11

Consider the Microchip TC1321 it's an I2C digital to analog converter (DAC) with 10 bits of resolution (4.88mV/step), available in SOIC8 (you'll need an easy to solder adapter board [eg sparkfun's or futurlec's) and operates from 5 volts. If you're OK with only 8 bits (19.5mV/step) consider the TC1320. Both chips are available from Mouser or Microchip ...

11

The best RC is infinite, then you have a perfectly ripple-less DC output. Problem is that it also takes forever to respond to changes in the duty cycle. So it's always a tradeoff. A first-order RC filter has a cutoff frequency of $f_c = \dfrac{1}{2 \pi RC}$ and a roll-off of 6 dB/octave = 20 dB/decade. The graph shows the frequency characteristic ...

11

All in- and outputs on most digital devices today have clamp diodes to the power rail. These diodes are there for protection of the device, to prevent a pin from having a higher or lower voltage than the supply rail. What you are experiencing here is that you actually power the DAC through its data pins and the respective protection diodes. Although the ...

10

To give a basic example of how a 1-bit ADC can be used to obtain useful information from a waveform, take a look at this circuit. It uses a triangle wave to turn the information into a pulse width modulated output. This is a similar but simplified version of how other 1-bit ADC techniques work, by using a (usually fedback) reference signal to compare the ...

9

A one-bit analog to digital converter (A/D) is just a comparator with the threshold in the middle of the range. Usually you don't call it a 1-bit A/D though, although it is legitimate to think of it that way. There are ways to make use of a comparator to ultimately get a higher resolution digital value. A delta-sigma A/D is one example. This keeps ...

8

A brown-out is a short dip in the power supply. Many microcontrollers have brown-out detection on-chip, often, like in the Atmel AVR, with programmable threshold levels. When a brown-out occurs the microcontroller will be reset. This may seem a bit drastic, but it's a question of reliability, and safety. If just one of those thousand of gates would lock due ...

8

These are decoupling capacitors. They are there primarily for two reasons: Power supplies take time to respond to a demand for more current from the device. The capacitors act as a local reserve until the power supply responds. Digital logic devices demand current very abruptly (due to the steep logic edges). The inductance of the power supply traces makes ...

8

I have in fact seen that before. I was working on an ADSP-21xx processor. The audio CODEC put the incoming data in signed 2's complement format. That particular day I was sending the data to a multi channel Maxim DAC that was expecting unsigned binary. Everybody around had a laugh at the Batman ears, then I added a few lines of code to get back to unsigned ...

8

Assumption: Based on the wording of the question, presumably certain input pins must not be floating to a "high" condition when the AD7541A is powered on. The conventional method of preventing a pin from floating, i.e. ensuring that it is held low until some logic state is imposed upon it by an external device, is to use a pull-down resistor on the pin in ...

7

Depending on what you are driving, if you have an Arduino you already have three to six Analog outputs, as you can use the AnalogWrite function to set the duty cycle of the PWM pins. The frequency is approximately 490 Hz, more than sufficient for LEDs (again, it depends on your application). You can set the value from 0 to 255, giving you a resolution of ...

7

This is very interesting. I decided to take a look at the concept of losing the most significant bit of a sine wave sequence. I did it for a half cycle of a sine wave and it does indeed lead to the wave shape in the original poster's question. The spreadsheet I created steps the argument for the sin() function from 0.00 to 3.14. It then scales the range ...

6

There are many many many many excellent existing on web tutorials on this.The following are excellent examples BUT you should have a look around as much has been written that will improve your general understanding far more than having people spell out again something which is so well covered elsewhere. This one gives a better than some concise explanation ...

6

The Due is the only Arduino board with a built in DAC. (Two of them.) If you need more than two outputs or want to use a board such as the Uno, then you need to consider building a DAC. Option 1: PWM Using a RC-filter you can create a low-pass filter that allows you to create true analog voltages from a PWM pin. This method could be difficult to ...

5

If it were me I would use an IC to do the DAC for me. The manufactures of the ICs take a lot of time and consideration for getting matched components and put them in the best configuration. The TC1320EOA is probably a good solution for what you want. It has I2C and in an 8pin SOIC configuration. I bet you will be hard pressed to get a design this small if ...

5

Most people drive the rungs of an R2R ladder with standard CMOS output pins. The "topology" directly connected to that output pin is generally a static CMOS inverter: where 'Q', Vdd, and Vss are physical pins you have access to, and 'A' is internal node of the chip. Some of them use a few CMOS output pins on a microcontroller to directly drive the R2R ...

5

I haven't looked at that datasheet, but what's wrong with the usual method of putting weak pulldown resistors on every pin that you don't want to float? If these are CMOS inputs, then 100 kΩ should do it. If you think there might be a lot of noise, you can use lower values. Assuming these pins are driven by normal digital outputs once everything is ...

5

R-2R is never done, it consumes to much area, it matches extremely poorly, has too high parasitics, etc. etc. Switched capacitor cells and techniques and almost certainly differential design will hold the day. If your process is digital rich and analog light, then a sigma delta approach will give you the right results. "Norsworthy, Steven R., ...

4

This sounds like there is some DC Bias removal taking place. In general with audio you want your average voltage should be 0v. This is because of how speakers work. 0v would mean that the speaker is at rest. In order for the speaker to sound normal you want it to be able to go back to its resting position. In order to achieve this, sound cards will remove ...

4

This is the case where reading the datasheet is truly the best thing for you to do -- they will tell you exactly how to initialize, start [and stop], and use both an ADC and DAC. Since you haven't named a specific MSP430, ADC chip, or analog signal characteristics, I'm guessing that the design is very much in the initial planning stages. I suggest nailing ...

4

You can do your entire project in a desktop PC. In fact, if I had to do it, I would start with the desktop: a .wav file is already sampled at a high frequency, often 44100 or 48000 Hz. determining the highest frequency can be done with an FFT. For prototyping, I would link FFTW. downsampling to an arbitrary frequency is a bit hard, because downsampling ...

4

The feedback pin is expecting a DC error voltage, with some usual stuff (ripple, noise, etc.) riding on it. The analog voltage loop is bandwidth-limited so that only useful information is used to determine the duty cycle of the converter. The easiest way is to use a DAC output and a series resistor to either sink or source amount of current out of / into ...

4

DACs have different requirements depending on the application. You'll find high precision solutions using expensive components to get good absolute precision, but in audio you don't need that. Linearity is the most important parameter. Since you'll be using an ATmega2560 which comes in a 100-pin package you can probably spare 16 I/Os, and then I would ...

4

That's easy to answer with a general answer and immensely hard to answer in full detail that people have been writing books and papers about it for decades. I've had some personal experience of this about 10 years ago when I implemented what was meant to be a simple and cheap SD converter (other side of same coin) with a mix of hardware and software and ...

4

In my other answer I focused on the high voltage, which is a problem for many components (and which David doesn't cover in his answer). You may also do most of it at lower, logic levels, and only go to 20V at the end. The HCMOS outputs of your microcontroller, or external logic IC, have a complementary MOSFET output, capable of both sourcing and sinking ...

4

The $\mathrm{W/Hz}$ may be a bit confusing as it looks like it refers to a single frequency. But that's just the dimension, it actually refers to a bandwidth, which is also expressed in Hz: maximum frequency - minimum frequency. So it's the power over a given bandwidth. If you divide power by the load's resistance you get voltage squared. So for a given ...

4

The second is nominal, not mean. But yes, height is 0.95 mm minimum, 1.00 mm nominal, and 1.05 mm maximum. The difference between mean and nominal is that nominal is the target dimension, that's the aim. Mean usually means arithmetic mean, but that may deviate from nominal, depending on spread. This could be a statistic on the package thickness. ...

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