For my project I will use 8 accelerometer(50G, 100G, 250G) (5-7V) and 1 pressure sensor (70PSI) (10-15V). Unfortunately the USBizi processor provides only 8 analog inputs.
I’m not very good with electronics, but I saw in this forum, that there is the possibility to use an ADC on the SPI to create more analog inputs. I would like to have a very high sampling rate on the inputs. Unforuntately I can not find the ADC
Can anyone help me or recommend me a suitable part?
the 12bit refers to how many bits the ADC reads at. 8 bit will only get you 256 variations of value, the FEZ has 10 bit, or 1024 possibly readouts, 12 bit gives you 4,096 variations of value.
Think of it as a scale… with a 2 bit ADC you have possible values of:
1, 2, 3, 4.
Not very useful. If you had a voltage range of 0-4.0v, you’d only be able to read 1, 2, 3 or 4v… nothing in between.
With a 4 bit ADC you could read 16 values… so if reading 1-4v, you’d get upto 1/4 volt accuracy.
Now go to 8 bit… and you have 256 values, from 0-3.3v, you get ~12mv accuracy. Not so accurate.
10 bit over 0-3.3v gives you ~3mv accuracy.
12 bit from 0-3.3v gives you ~0.8mv accuracy - now we’re talking!
As Mark said, the bit-rating on ADCs show how small an increment the measurement can take. The larger the number, the closer the gap between each successive measurement is. The question for you is - how accurate do you need it to be???
SPI is “serial Peripheral Interface”. Serial means single bit at a time.
If I were you I’d do two things. Ditch the idea that you want so many devices at once, and connect a pressure sensor and an accelerometer directly to your Fez and make that work. In the meantime order the chip I mentioned (or any other one you decide). Then when it arrives you’ll have figured out measurement with the ADC directly on Fez, and you will be better able handle the SPI connection
Guys, thank you so much for the good advice and good links. I’m going to spend now sometime in the internet and find out what I really need
@ Gus: The digital accelerometer go for some reason not high enaugh. Max I saw was like 18G, but we would like to be accurate at around 40G and again at around 200G. I found a digital pressure sensor, but its just twice as expensive as the analog sensor (and we are probably going to destroy some sensors during development…)