# Tag Info

8

Does that sound reasonable? Or am I missing something? Theoretically SPL halves with a doubling of distance so, the extra attenuation over the distance range of 0.5 metres to 3000 metres becomes: - $$20\cdot log_{10}(6000)$$ And this is 75.56 dB hence, an SPL of 94 dB (at 0.5 m) reduces to 18.44 dB (at 3 km). This assumes a perfect scenario with no ...

7

Almost surely lookup table will be faster, but you shouldn't really be concerned with speed when you're talking about reading temperature, with a doubtless glacially slow thermistor at that. Unless you're talking about 1990s 4-bit mask-programmed micro running off a watch crystal, that is.

5

the range of the signal is such that the 10 bit ADC value is moving from 200-500 (1V-2.5V) on a scale of 0-1023(0V-5V). You are right at the point where it’s tricky to get a decent benefit without significant attention to detail. Currently you occupy a range of 1.5 volts (1 volt to 2.5 volt) out of 5 volts but, you don’t really have a useable range of 5 ...

4

4.6 A gives about 1219 mV. 1219 mV ---> 1513 counts 4.6 A ---> 1513 counts ??? ---> 1 count? Ans: ~3.02 mA

4

thermistors that are around 100K Here's a problem, the 2N7000 has an $I_{DSS}$ of anything up to 1 uA on a good day and, depending on ambient temperature can be several tens or a hundred uA leakage: - That current flows when the device is off and so, depending how many switched off channels you have will determine the volt drop error across R1. Given ...

3

If $R$ is the resolution as conventionally defined, then $$R = \frac{V_{REF}}{2^N}$$ where $R$ is the resolution in volts, $V_{REF}$ is the internal reference voltage for the converter, and $N$ is the number of bits. The resolution is the smallest observable change in input voltage (for an ADC) or the smallest possible change in the output voltage (...

3

I don't know that "faster" is your concern. The lookup table will always be faster, even assuming you need to do a linear interpolation between two entries (which you should do with integer math!!). The lookup table may or may not use more memory, keeping in mind that you might need to load floating point libraries to use the Steinhart-Hart equations. I ...

2

Take a look at the example circuit in figure 44 on page 36 of the datasheet: There's your mysterious capacitor across the differential inputs again. Now scroll down to page 38 and have a look at section 10.2.2.6 "First-order RC Filter Considerations" Although the device digital filter attenuates high-frequency noise, use a first order low-pass RC filter ...

2

Here's the relevant part of the datasheet that you linked:

2

Assuming you store(MAP) the whole lookup table in the RAM memory there is no need to compute anyhthing further. This will be the fastest. The search will also be faster as the data is stored in ether increasing or a decreasing order. The MCUs depending on their capacities might try to match the speed but on an average, the look up table will be fastest.

2

The LM35 datasheet says absolute maximum rating for supply voltage is -0.2V. It means that connecting it the wrong way to a power supply can damage it, and it does not have to work any more as the absolute maximum ratings have been exceeded. Also the minimum recommended supply voltage is 4V, so check that your supply voltage is also 4.0V or more. It may ...

2

Good circuit. For clean measurements, place a single 1uF capacitor at input to ADC. This cap, along with 50,000 ohm source resistance, forms a 0.05 second time constant. Given, using the concept of NEPER where a neper is 8.6dB per time constant, if you want 86dB accuracy, you need to wait 10 time constants, or 0.5 seconds, after changing to a different ...

2

Your approach is plausible. On state resistance is about 13 ohms. This is very unlikely to effect the expected temperature accuracy. At a very low current, the actual ON resistance will be still lesser. Provide sufficient amount of time after switching to the test channel and before scanning the ADC and a small value of capacitor at the input of the ADC. ...

2

simulate this circuit – Schematic created using CircuitLab If you have need a resistive divider, it can limit current instead of an explicit current limiting resistor. The diode rail clamps can only clamp to the rails if there is voltage on the rails. They won't offer protection if the ADC is unpowered. But zeners or TVSs which breakdown in reverse ...

1

Inverting converter, -30 -> +30 provide 3.3V -> 0V

1

Your output step size is 1LSB, but the maximum distance (i.e. error) away from your truly desired value is 1/2LSB, when the desired value is halfway between two steps and you cannot get any closer to it.

1

You can offset the signal. simulate this circuit – Schematic created using CircuitLab The output of the circuit above is the input signal having an offset of VDD/2. I didn't show an exact value for C1 (coupling or DC blocking capacitor) because it depends on the frequency of the signal. Note that C1 and parallel combination of R1 and R2 form a hi-...

1

I wouldn't choose this tack, because the negative-going signal would not be within the range of allowable input signals on your microcontroller. Note that for the STM32f405 the absolute minimum input for a 5V tolerant pin is $V_{SS} -0.3$. The way this is done is to offset the input signal to be midrange for zero input, attenuating if necessary. Note ...

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