I'd like to make a datalogger for several sensors. Most of the sensors are analog and I know I will need an A to D conversion. I have found out how to do that. However, one of the "Sensors" is an array of four swithches that can have a number of off/on settings.
This is essentially digital data but I don't know how to capture it. Would I have to get the on/off value for and log it for each switch individually and later process it, or is there a way to get all of them and convert it to a four digit digital value.
Are you looking for a do-it-yourself circuit, a kit, or a store bought solution?
Are the switch contacts available for you to hook up GND and some pullups? Or do the switches output a voltage? Is it AC or DC? What voltage levels are the ON/OFF settings?
Does the switch voltage have to be isolated from GND? How about the analog voltages?
How frequently do you need to log data?
How many is "several" analog inputs?
Is the analog input voltage AC, DC or both? What is the range of voltage to be read? Are overvoltages a possibility? How much noise is going to be superimposed on your analog input voltage?
What kind of accuracy do you need on the analog inputs? One part in
256, 1024, 4096, 65536? All of these are available, with progressively more cost as precision increases.
You want datalogging to what? Do you want to buy something that has a chart recorder built in, are you putting this data in an Excel spreadsheet, or do you want to use this data to control something else?
Is this data going to go to a PC? If so, are you anticipating writing a program to get or use the data? If so, what programming language are you using?
How about the price/quality/service balance? Describe more about your project, so someone else can get a feel for whether you need a Yugo, a Chevy or a Cadillac.
There are so many different good answers to your question, depending on how you define your project.
Some idea of the scope (how many, how much $$, how much effort, how powered, how hot, how fast, how accurate, how soon, ...) would help.
Without knowing any of that, the answers you get here are just guesses.
With that in mind, if I were doing this I'd probably get one of the inexpensive USB gadgets from
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either the miniLAB 1008 or the USB-1208LS, and hook it up to an old but still working laptop PC. A bit of PC-side software and you're done.
If you want or need to roll your own, there are a ton of inexpensive microcontrollers with A/D and (of course) digital inputs. If you are using a PC to log the data, add some signal conditioning and you're almost done. Otherwise, stick on a cheap I2C flash/eeprom memory chip.
Of course, if what you're logging needs 16-bit precision at 100 Msps and has to work through impact with a concrete wall at 600 kph, then the answers might be slightly different.
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