Choosing a microcontroller

[phlebire]

Hello everyone,

I am looking for a microcontroller with specific needs, and I am pretty new to all of this (currently an intern in a small company still haven't finished my engineering school yet).

The microcontroller would be controlling 2 transistors (independantly) and storing regularily an analog reading. So i need a ADC and 2 other pins. These readings from the ADC must be stored and are likely to go on for a few weeks. I would like to be able to get this data (like dumping a buffer) to my computer to be able to analyse all of it. My application works at max 3.3V and the ADC precision would be of 0.01 V if possible).

Here is the tricky part: i need as many ADC as possible. I have described only one sample but my testbench will include about 100 of these samples.

I was recently introduced to the Teensy microcontrollers but obviously they are too expensive even though they would have worked perfectly. (20$ each, and I would need one for each 8 samples...)

Has anyone any idea of the microcontroller of my dreams? ;-)

 

[barry]

Several questions:
1) Are you saying you need to sample 100 different inputs, or 100 samples of a single input; it's not clear from your post.
2) Precision and accuracy are not the same thing. What ACCURACY do you need? 8-bit? 24-bit?
3) Are you saying you need to store "a few weeks" worth of data? Unless you are sampling very slowly, you're going to need external memory.

In the meantime, look at the Microchip PIC24 series of micros. You can get them with up to 24 analog inputs (maybe more, I'm not sure). But if you need 100 analog inputs, you're going to need to add external multiplexers.

 

[phlebire]

Thanks for the quick answer

1) I will need to sample 160 (sorry, not 100) different inputs. This means 160 ADC and 320 I/O pins. Of course this is a lot and I guess I will be needing a few microcontrollers but the less the better and the cheaper I guess!
2) I'm not shure how much accuracy I need, to be honest. If a microcontroller is supplied with a 3.3V voltage and I want about 0.01V precision i guess i will be needing arround 9 bits accuracy for the 0-->3.3V range. But I guess 8bits accuracy should be enough (0.013 V accuracy).
3) Yes I will be needing to store for EACH sample about 1 measure per hour. The test if my calculation is right should go on for about 20 days. But like I said, if there is a buffer in the microcontroller that I can dump to my computer via USB or other peripheral, I can do this dumping every 2-3 days.
So i guess if we are able to sum up all all the samples it would mean 8bits * (24 measures per day * 3 days ) * 160 samples = 92'160 bits.


I will be looking in the meantime at the PIC24. It would seem like a good answer to my problem If you have any better solution please let me know !

 

[barry]

You don't need 160 ADCs, you just need a bunch of multiplexers. For example, you could use a PIC24FJ256 which has 24 10-bit AD inputs. If you put an 8-channel multiplexer on each analog input, that will give you 192 inputs. Depending on your requirements, you could get away with a very inexpensive mux like a CD4051 (< $0.50 US). The PIC has 96 Kbytes of memory which might just be enough for you, or you could use an inexpensive SPI flash to store your data.

 

[bigdogguru]

The following is an informative blog post concerning the use of CD74HC4067 which is a 16-Channel Analog Multiplexer/Demultiplexer in conjunction with the ADC of an Arduino:

Muxing Around With The CD74HC4067 + Arduino

You could use a similar technique with the PIC24, ARM, etc.


BigDog

 

[josiphal]

There are cheep MSP430F5510 entry USB family. It is working on 3.3V, and have ADC. It can collect data and store data it in simple TXT file (RAM/Flash on chip combination), and when you need it on PC, just plug it like any other USB memory stick, open file and that's it.

https://www.elektronika.ba/forum/viewtopic.php?f=23&t=9331&start=20#p122363

 

[phlebire]

First of all thank you all so much for these answers.

I will be looking at all of these possibilities and comparing prices.
I must say the MSP430F5510 seems like a nice option just for the sake of simplicity even though the forum you have linked me to is in a foreign language ^^

 

[josiphal]

Check if the MSP430F5510 price fits to your budget. It can be programmed/flashed directly from PC USB with zero-parts or without any glue logic between, no need for flashing/programming tool. I just linked to that forum that you can see pictures of present USB device on PC like any other USB stick, and opening file stored on MSP430F5510. This is part of TI USB stack, open source examples.