Dear Experts,
Hi,
for a project I need to get all 12 ADC channels of an ATMEGA32U4 based board to work concurrently.
But I would like to know following answers :
1. what is the maximum frequency sampling for each channel? ( suppose input clock of board is 16MHz).
2. Is there any interrupt based open source code that i can use?
BR
Mehrdad,
The 32u4 has a single channel ADC with a multiplexer in front of it. you cannot sample all the channels at the same time.
The datasheet has all the sampling information
Jim
You get an a/d reading every 100usec or so, so 12 of them will take 1200usecs. What rate do you need?
Hi again,
and thanks for the answer,
Dear Jim,
By concurrent I mean I would like to make all 12 channels work.
I get one sample from first channel and one sample from second channel and ... and loop it again.
Dear Bob,
I need maximum speed of 1000 samples per second for each channel now. ( for ECG project).
But could some body give me a hint how to develop intterupt based 12 channel ADC program?
BR
Mehrdad,
What is the source of the interrupt? The ADC upon completion of a conversion?
Code would be simple enough.
Set up a counter to count from 0 to 0x0b(11)
mux channel = count
Set up the ADC for interrupt on conversion complete
Start the conversion
Sit in a loop until interrrupt fires
When interrupt fires save the result from the ADC in SRAM
Increment count
mux = count
start ADC
return
I did not include anything for noise reduction etc. my example is crude to say the least. Do a search in the forums. There is something there.
Jim
I need maximum speed of 1000 samples per second for each channel now. ( for ECG project).
Should be do-able. For max 10bit resolution the ADCs can do a maximum of 15,300 conversions per second. You look like you need 12,000 per second.
Once you get these 12000 samples each second (using 10% to 20% of processor), where are you going to put them on an AVR8? How much processing is needed and how often? As you mentioned a USB-enabled AVR model, I'd guess you plan to send stuff out via the USB. Lessee-- I guess that I'd put all 12 samples into a packet, 25 bytes plus overhead. Isn't USB once-a-millisecond? So it would "just work" if you >>never<< were too busy on the other end to swallow a packet?
Should be do-able. For max 10bit resolution the ADCs can do a maximum of 15,300 conversions per second. You look like you need 12,000 per second.
From previous work and discussions here, each channel had better have very good "drive" to avoid cross-channel effects.
Now, I'm not an expert Xmega user, but round-robin conversions and DMA buffers and inbuilt USB sounds like it was made for this.
Thanks again for answers,
I think for every channel we could get more than 15000 samples per second not for all the channels.
But as I work on LUFA project, I would rather find some peace of code for interrupt based ADC conversion to put inside it.
I dont know how to define interrupt routines for LUFA project uder linux avr compiler yet .
Now I am going to surf the web to find some thing useful.
BR
Mehrdad,
