I need to acquire some analog signals and read a digital signal at fixed sampling frequency.
What is the correct way for do this?
Note that this is not trivial because during the acquisition process, at given sampling time, the digital signal can missing due the fast sampling rate respect to the digital signal frequency.
For example think at digital square wave of 50Hz frequency and a sampling rate of 100Hz.
You can check for a suitable data acquisition system. For example Dewes oft data acquisition systems are really easy to use and have highly flexible software that requires zero programming to acquire, store and analyse the data.
They offer interface to any analog signal and sensor and also offer digital data buses like CAN bus, CAN FD, XCP, EtherCAT, EtherNET, video, and others.
Related
I am using a PIC24 microcontroller and have multiple inputs. Via these I would like to obtain analog voltage data as fast as possible. I have 8 different data arriving to the microcontroller and I am a bit confused how to solve the problem.
My first idea was to to read in the data sequentially. First from AN0, then AN1 and so forth, but this may take quite a while and I am not at all sure it would be fast enough to do without any other trick. Especially because I do not only want to read in one single value per pin, but an array of voltages, then store and numerically integrate and send the results through USB to the PC. While doing so, new data should be constantly received via the aforementioned pins.
Is it feasible at all what I'm trying to achieve here?
Thanks in advance :)
You should think through your requirements a little more, especially the "at the same time" and "as fast as possible" statements. If you sample each channel within 10 to 100 microseconds of the next would that be satisfactory? What is the maximum frequency of the input signal that you need to detect? Your sampling frequency should be at least double the maximum signal frequency of interest.
Use a single ADC with enough input channels. Configure the ADC so that each time it is triggered to take a sample it will sample all of the channels in sequence (multichannel scan). It won't sample all 8 channels at literally "the same time", but it will cycle through each channel and sample them one after the other at nearly the same time. This could be within a few microseconds depending on the clock rate of the ADC and the channel setup time that you configure.
Now you could configure the ADC to sample in continuous mode where it would start the next sample scan immediately after finishing the previous scan. That would be "as fast as possible" but that might be faster than you need and produce more data than can be processed. Instead you should choose the sampling rate based upon the input signal frequency of interest and setup the ADC to sample at that rate. This rate might be much less than "as fast as possible". You might configure the ADC to collect one sample per channel when it is triggered (single conversion mode) and also setup a hardware timer to expire at the desired sampling rate and trigger the ADC to take a sample scan. The sample period (time between samples) must be greater than the time required to scan all the channels because you won't be able to trigger the ADC again before it has completed the previous channel scan.
If you really need to sample all channels at literally the same time then you probably need a separate ADC for each channel and then trigger all the ADCs to collect a sample at once.
I am trying to get the dangerous value of LPG leak using MQ5 Gas sensor. But I don't know the value from serial monitor that the analog reads. Is the output of gas sensor in ppm?
You need to provide more information for people to help answer the question. You need to provide a circuit schematic, how you are interfacing it to the microcontroller etc.
However, it is unlikely you are getting a PPM reading from the sensor unless you have calibrated the sensor and developed a function to convert voltage (or resistance) to a gas concentration. First of all, you typically need to calibrate the sensor by exposing it to a known concentration of the analyte (gas) and measuring the voltage / ADC reading. Second, those types of sensors usually have non-linear response to the gas concentration, therefore developing a calibration function is difficult (and you need to characterize the sensor's response to different levels of gas concentration to develop an algorithm). There are many ways to do this, but that can be an expensive and time consuming process. What compounds the problem is that different sensors typically exhibit different responses to the same gas concentrations between batches or even two sensors from the same batch. The sensors are also sensitive to temperature, relative humidity and other contaminants which can skew the readings. These sensors can be useful for generally detecting the presence of the analyte (gas), but typically aren't very useful or accurate when estimating PPM within a reasonable error margin. There are also many variables to control with that sensor such as the heater voltage, heating pulse duration, load resistance, etc. These sensors have MANY cross sensitivities and responses to other analytes (other than LPG).
If you have implemented the sensor as per the manufacturer's data sheet and have converted the resistance into a usable voltage and are reading the values from an ADC, you may be able to interpret the ADC readings as general indication of the presence of the gas (but maybe not.. you could be measuring humidity fluctuations), in any case you would likely need to calibrate the sensor and develop an algorithm to estimate the PPM.
It appears from looking at a couple websites that this sensor returns the value of Rs (sensing resistance).
Looks like you will have to calculate a ratio of Rs/Ro (Ro being the resistance of "clean" air) for which you would derive the ppm from the MQ5 datasheet graph.
I want to ask about I Beacon advertising, especially Tx Power.
I used two BLE module HM10 and HM11. I make one as a ibeacon (HM10). and other one used to connect and listen to HM10 broadcasting.
I used MCU ATmega32 AVR tied with HM11 and I used scanf function to read the broadcast. I want to extract the last byte (Tx Power). I want to measure the distance with AVR programming.
Could you tell me the algorithm?
The formula Apple uses to calculate a distance estimate to an iBeacon is not published. There are a number of alternative formulas including this one, based on a best fit power curve, that we wrote for the Android Beacon Library.
Further research we have done shows that the formula above basically works, but it has two main imperfections:
It does not work well for weaker beacon transmitters. With weaker broadcasts, the distance is underestimated.
It does not account for varying signal gains in receivers. Different receivers have different antennas and receivers which measure the same signals differently.
There is an ongoing discussion of the best formula here.
A bit late but hopefully useful to others. I have given up on Apple's "Accuracy" number; as #davidyoung points out, different devices will have different signal gains. Now I am not an engineer but more of a math and statistics person, so I have gone down the route of "fingerprinting" an indoor space instead. Essentially I read all RSSI from all beacons installed in a certain "venue". Some might not be within reach and therefore I just assume, in such cases, an RSSI of -95 dBm (which seems to be the floor past which a signal is not read any more). Such constituted array has the same beacons in the same positions at all times (even across app launches). I compute a 5 seconds moving average for each beacon (so a I se 5 arrays to do that). The resulting avg array is then shifted up by 95 units and normalised so that the sum of all of its values is one. If you want to tag an an indoor "point" you collect many of these normalised average arrays on that specific spot. I go ahead and construct a database of "spots". To forecast your proximity to any spot in a database you simply compute a quadratic distance of your current reading and the all of the fingerprints in the database.
Which beacons to use? At least class 2 in power. How many? At least a couple per room (put them in two adjacent corners, on the ceiling or high up).
The last step that you need to do is match the fingerprints with an x,y coordinate on your map. I never did this step, because I am mainly interested in proximity applications and not fully fingerprint and indoor space.
Perhaps the discussion above will serve you as a guidance on a technique that is used by many indoor location companies.
Disclosure: I have recently open sourced my code doing the above calculations.
I am using Arduino UNO board. I have 24 analog channel which gives me 0~5v analog out put. Now my problem is I have only 5 analog channel. I wanted to read value from each channel for every 2 min and then switch to other channel. Can anyone suggest me in Hardware how can get analog value ?
I am planning to use 8:1 multiplexer or 16:1 multiplexer . Will it is correct way of doing it. Can you suggest other way of doing it in hardware ?
74HC4051,74HCT4051,ADG708,MD14051B,
IC I am planning to Use.dep[end on so,s1,s2 just switch the channel
As a start, you might need to know that even Arduino Uno also have internal MUX. In my experience of reading multiple analog channel, this is the approach that I take. However by taking this approach, I suggest you to recheck the analog value so adding MUX will not generate any error or bias.
This could be done by comparing the output of measurement with the MUX and output of measurement without the MUX. I used 74HC4051 and it works brilliantly, just make sure not to leave any pin floating. The only disadvantage of this method is that you will need to use some I/O to control the MUX, but if that is not an issue for you, then go ahead.
Any other method could be more complicated. It would require your analog channels to correlate with each other, and you need to find a way method to combine multiple analog channel into a single channel.
e.g: if your aim is to compare two analog value, instead of measuring the value and comparing the value in software, you could make use of op-amp comparison circuit to compare the value for you and take the comparison result instead.
Use the photon-pixel coupling method, it is a new approach in science for sampling an unlimited number of sensors in parallel.
Basically, each sensor output is an LED. If you have 10000 sensors, the output of all of them is inserted in a LED array, a LED matrix as the authors say. After that, the LED array is filmed by a video camera and the images are processed in real time by a computer. A software reads one pixel from each LED from the LED array and converts it to numerical values. So, your LED array will be converted in a matrix (with 10000 elements) filled with numbers that can be processed as you wish in your software. I don't know if I was explicit but you can read their article here: https://www.sciencedirect.com/science/article/pii/S2215016119300901
Note that classic multiplexing is serial, this approach is parallel.
The photon-pixel coupling method is truly ingenious because it solves two main problems in engineering: an unlimited number of sensors and their parallel sampling at video rate frequencies. Just imagine, we can read as many sensors as we wish. What I wander is if we can adapt the photon-pixel coupling to Arduino. I am new in the world of microcontrollers but I know Arduino can support a cam, so it should be possible.
If you are a PhD student then:
P.A. Gagniuc, C. Ionescu-Tirgoviste, R.G. Serban, E. Gagniuc. Photon-pixel coupling: A method for parallel acquisition of electrical signals in scientific investigations. MethodsX, 6:968-979, 2019.
To read more analog channels than inputs you have, an analog multiplexer is a good option. All the ones you suggested will work, but personally, I like the Analog Devices ICs for analog circuits, so I would take the ADG708, but this is just a personal preference.
I have been working on a ARM cortex A8 board on mp3 decoder.
While doing this i have a requirement saying the mp3 decoder solution i am doing should consume 50 milli-watts of power. This generated few questions in my mind when i thought about it:-
1.) I recall that there is some relation between the Core Voltage applied(V), the clock frequency(f) of a processor and power consumed(P) as something like P is directly proportional to the voltage and frequency squared. But is the exact relation. Given operating clock Frequency, voltage of a processor, how can we calculate power consumed by it.
2.) Now if i get the power consumed from step 1.) at some clock frequency, and i am told that the decoder solution i am giving, can consume only 50 milli-watts, how can i get the maximum limit on MCPS, which will be the upper bound on the MCPS of my decoder solution running on that hardware board?
Can i deduce that if power obtained as in step 1.) say P, is consumed at frequency F, so for 50 milli-watts power, what is clock frequency frequency and calculate accordingly the frequency. And then call this frequency as my code MHz (MCPS) upper bound?
Basically how does one map(is there any equation) power consumed by a software to MCPS consumed
I hope this is relevant here, or should it go to superuser?
Thank you.
-AD.
It really depends on the architecture.
From their own page:
Core area, frequency range and power consumption are dependent on process, libraries and optimizations.
Power with cache (mW/MHz) <0.59
<0.45
Basically, it states that you can't accurately calculate the power consumption, so your best bet would be to do some measurements yourself. Try to run a full CPU-usage application and meassure the power consumption. It will give you some idea of the max-load, which will be a good start for you (to know how much you need to optimize your code and insert idle points).