hello. i am new , and tried to google this with no straight answer to my surprise.
a/
i an working on a project that consists of around 100 inputs, mainly analog.(temperature,dissolved oxygen,liquid levels etc).
what is the common hatdware setup to feed my board with such multisensors task.
thanks.
Some would use banks of multiplexers, some would use external ADCs, perhaps with analog muxes in front of them.
I would go 8-channel ADC chips with SPI interface. 12 chips would allow 96 inputs, with no muxes and their inherent resistance to screw up your signal.
MCP3208 is 8 channel, 12-bit ADC, very easy to use.
Set the SPI clock to 2 MHz (SPI divisor of 8 ), takes 3 SPI transfers for a conversion and to receive the data.
(1/16000000) x 8 x 24 = 12uS.
96 channels, 1152uS, plus whatever time for code to cycle thru addresses, and manipulate and store the data into an int-size array.
Is it just me and IE11, or does the forum screw up links for everyone else too? Sticks extra http:// http// at the front of links, and a " at the end.
The main question is, what you want to do with so many signals. Measuring is only the first step, what shall happen afterwards?
Using 100 analog inputs with one ADC may not work, because many values deserve some raw to physical conversion before further processing. At least you'll get a very low overall data rate.
Using additional external ADC will speed up the conversion (parallel instead sequential), but doesn't help in calculating cooked/scaled values from raw inputs. You may be better up with dedicated sensor modules, which not only provide the scaled values, but also transmit them over an digital bus. Or use multiple controllers for collecting and converting a number of analogous signals, when computation speed is critical.
Digital transmission does not suffer from electrical noise, which tends to affect analogous signals. As a rule of thumb, put the ADC as close to the sensors as possible, and transmit binary data over longer lines.
DrDiettrich:
The main question is, what you want to do with so many signals. Measuring is only the first step, what shall happen afterwards?Using 100 analog inputs with one ADC may not work, because many values deserve some raw to physical conversion before further processing. At least you'll get a very low overall data rate.
Using additional external ADC will speed up the conversion (parallel instead sequential), but doesn't help in calculating cooked/scaled values from raw inputs. You may be better up with dedicated sensor modules, which not only provide the scaled values, but also transmit them over an digital bus. Or use multiple controllers for collecting and converting a number of analogous signals, when computation speed is critical.
Digital transmission does not suffer from electrical noise, which tends to affect analogous signals. As a rule of thumb, put the ADC as close to the sensors as possible, and transmit binary data over longer lines.
thanks.
the rate of sampling those sensors is over relative long periods.(we are talking here greenhouses modules)
these are water levels, water temp, ec, and some solution values.
one thing is that control is about 50 meter away from the sensors.
the outputs are watervalve relays, thermal screens motors, fans, etc.
all has to be logged into a database,
i thought using several adc's over a bus (how far can these locate from the master board?)
thanks for commenting.
Oded.
osamuel:
one thing is that control is about 50 meter away from the sensors.i thought using several adc's over a bus (how far can these locate from the master board?)
Several ADC's are required with such long connections. I'd also suggest a reliable (industry grade) digital bus system, to connect the remote components to your central controller. Details depend on the electrical environment, how much noise such a bus must sustain. Cheap yet powerful data processing cannot help when the data acquisition doesn't work properly.