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10 votes

ADC clock and sampling rate using FPGA

In the AD9226 datasheet, Figure 1 at the bottom of page 3 shows you one output sample per clock. The sample rate is therefore the same as the clock rate. In the switching characteristics table also on ...
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9 votes

How can a DMM measure open circuit voltage?

Try putting some numbers on the effect of internal resistance. A small battery such as an AA might have an internal resistance in the range of 1\$\Omega\$. Multimeters usually have input resistances ...
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9 votes

ADC stops functioning when cold

Given you have systematic failure across two different batches made in different ways, I think it is less likely to be a manufacturing issue. Still possible though. Two other possible causes came to ...
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7 votes

Which noise sources dominate in a receiver?

It's a compromise. You can easily make thermal noise dominate by adding an LNA stage with enough gain that the thermal noise exceeds the quantisation noise. Then strong signals will exceed the ADC's ...
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6 votes
Accepted

How can A/D conversion perform linearization of nonlinear I/O behavior of sensor recordings?

Assuming a 16 bits ADC, you have \$2^{16} = 65536\$ possible numbers. Instead of linearly mapping these numbers to a value range (e. g. 0.0 to 5.0 V) you build a Look-Up Table with 65536 entries and ...
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  • 6,103
6 votes

Smooth wave plotting using 3 inch thermal printer

Without reading the datasheet, it is obvious from these lines that you operate on a number of bits: ...
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6 votes

How can a DMM measure open circuit voltage?

A DMM may have an internal resistance of 10 mega ohms. So the current drawn is small enough that it doesn't cause an issue for typical usage. But see "burden voltage".
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6 votes

ADC stops functioning when cold

TL;DR: The ADC is on an analog ground plane that is connected to the digital ground plane by a single segment 10 mil trace, about 1.3" away from the ADC, away from digital signals straddling the ...
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5 votes
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How can a DMM measure open circuit voltage?

Let's have a look a multimeter mearuring the voltage from a battery: simulate this circuit – Schematic created using CircuitLab The battery contains a perfect voltage source and an internal ...
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5 votes

ADC stops functioning when cold

Change of behaviour due to temperature variations may also be due to timing issues on the digital interface. I would suggest you review the implementation of the digital interface (clock speed, clock ...
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4 votes
Accepted

ADC doesn't start from 0V

1M\$\Omega\$ is too high for the on-chip ADC source impedance (it depends on how you are using the ADC, and the information is in the MCU datasheet, I'm not going to evaluate how you are using it, ...
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4 votes

ADC stops functioning when cold

It’s probably a bad solder joint but it could also be a damaged plastic package. You can find an entire application note on dealing with that particular package here. Note that the typical reflow ...
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3 votes

Different combinations for ADC input protection for measurements

Z-Diodes have significant leakage currents below their clamp voltage. This affects the linearity in version "B". In "A" you have more headroom for VZ and hope the clamp diode in ...
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  • 418
3 votes

MCP3008 question about voltage

Data sheet for MCP3008 specifies Vref = 5V and Vdd = 5v. The datasheet specifies: Take note that \$V_{REF,max} = V_{DD}\$. If \$V_{DD} = 3.3V\$, you can't supply \$V_{REF}\$ any higher than 3.3V. ...
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  • 1,063
3 votes

Use ADS1115 to measure voltage

From the datasheet: You can see by looking at the absolute maximum allowed analog input voltage, you are exceeding the range of the device. Two of those cells in series is outside that range, and ...
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2 votes
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ADC stops functioning when cold

After several months dealing with this issue, the moment of realization came to me at 4 AM as I was drifting off to sleep. The SYNC Line The ADC has an external synchronization feature that allows ...
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2 votes

MCP3008 question about voltage

The MCP3008 has two input voltages, VDD and VREF. VDD is your supply voltage, and is used to power the internal circuitry of the chip. This means that your communication interface (SPI it looks like) ...
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2 votes
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ADS1115: Using 5V supply instead of 3V, do I need to increase the logic level signal from 3V to 5V?

Never assume. THe first place you should check for this kind of information is in the datasheet: But you also have to pay attention to the operating conditions header under at the top of the section ...
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2 votes

Which noise sources dominate in a receiver?

Thermal noise tends to dominate in an RF receiver. The bit-depth can be large enough so that the corresponding quantization noise becomes less significant w.r.t thermal noise. Quantization noise can ...
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2 votes
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Measuring AC current with a current transformer and ADC

... the response time is slow to current changes ... This is a circuit that can give the "peak voltage" (positive or negative) every "cycle" and/or "half cycle". If ...
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  • 3,806
1 vote

Resistive Moisture Sensors, What is the purpose of the 2N3904 Transistor in the Sparkfun Circuit?

The sensitivity will be higher by a factor of more than 100 (typically) with the transistor due to the current gain of the transistor. That means slower corrosion of the sensor as well. Both circuit ...
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1 vote
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Overall CMRR of analog front-end

CMRR means that a tiny part of the input common mode voltage will be converted to the differential mode signal output. Therefore, subsequent stages cannot remove this common-mode-error anymore, ...
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1 vote

Which noise sources dominate in a receiver?

I appreciate the other answers given, but I'm adding this answer to my own question because I think I found a more detailed answer here. According to the author, it is typical to design for thermal ...
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  • 151
1 vote
Accepted

Can I drive a bridge sensing circuit with a voltage reference?

Yes, it's ideal to use the same reference (with or without a buffer) in a bridge measurement. That way the reference voltage cancels out in the ADC reading. As far as not drawing current from a ...
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1 vote

ADS1115: Using 5V supply instead of 3V, do I need to increase the logic level signal from 3V to 5V?

It depends on whether the MCU allows the I2C pins (which are open-drain) to be pulled above Vdd for the MCU. The ADS1115 needs 0.7*Vdd for a guaranteed logic high on digital inputs, which is nominally ...
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1 vote

How can a DMM measure open circuit voltage?

You never measure open circuit voltage. It’s not physically possible. But you can get arbitrarily close in practice :) Thus no multimeter can provide such a value directly, because measuring open ...
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1 vote

How to measure bit resolution

I am wondering how can I verify that I am getting the noted effective bit resolution? This is a very cheap and very good DC test I have used on all the ADC/DAQ systems I have ever brought into life. ...
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1 vote

How to measure bit resolution

You should get a suitable, linear signal generator with a dynamic range that is suitable to your system. If you can do an automated measurement even better, but essentially what you are doing is a ...
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1 vote
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PSRR of an amp + ADC input stage

First, is this the correct way to measure PSRR? It is a method of measuring PSRR but, if you are trying to find the PSRR of an amplifier under extended conditions you will come unstuck. This is ...
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