A/D Acquisition

[icare34]

Hello,
I have baught a MIAC module, but I have some questions :
I my application, I need to use analogic inputs.
1) Is there some analog low filter on analog input ? What is the cut-off fréquency ?
2) Do you have a équivalent circuit of the input ?

Each MIAC input (I1—I8) represents a resistive load of 10K Ohm, ±1%, to 0R when the input voltage is between 0V and 24V.

10K Ohm to 0R is not clear for me
3) The frequency of the sampling is important for me : what is the best way ? using interupt I suppose ?
4) I would like to implétent FIR filter (cf http://ww1.microchip.com/downloads/en/A ... 00852a.pdf), is-it possible ?
What is the bes way with Miac Module :
Using Flowcode 4 + Miac module ?
Using Flowcode 4 + PIC18F4455 module
Using a C compiler + PIC18F4455 module ?

Best regards

[Benj]

Hello,

Sean will be able to provide you with better answers but Ill have a go at the ones that I know.

2) Basically the input circuit just has a 10K resistor between the input and ground to provide a potential divider. Analogue sources should be connected between M voltage and input pin.

3) Interrupt based sampling will give you a nice fixed delay sampling input so is probably the best way to go if you want accurate samle points.

4) Yes this is probably possible but would require porting into Flowcode.

The easiest way is to use the MIAC is to use Flowcode with target set to MIAC and useage of MIAC component, Otherwise a C compiler compiled with an offset of 0x800 to allow for the MIAC bootloader.

[Sean]

The MIAC ADC clock is set to the RC option. This completes a conversion in approximately 20uS.
In addition there is an initial sampling delay of approximately 20us.

If necessary, both of these settings can be changed using the Custom Code feature in Flowcode V4. The settings can be accessed in the InputANALOG macro code.

The sampling delay is controlled by the line:

#define MX_ADC_SAMP_TIME 40

The value 40 represents approximately 20us.


The clock source is controlled by the line:

adcon2 = 0x03;

Due to the high clock speed of the MIAC, the only alternative value for this parameter is 0x06 (Fosc/64 = 750KHz), which will result in a conversion time of 15us.


The MIAC input circuit:

MIACin1.jpg (12.18 KiB) Viewed 14398 times

The 0R terminal is the common reference for analog and other low noise signals.

[icare34]

Thanks a lot for these informations.

[icare34]

Hello,
For my application, it will be difficult to implement FIR filter.
So, I try to implement a hard low pass filter.
I've seen that there are two AZ324M-E1 near analog inputs.
Is-it use as low pass filter ? If yes, what is the cut-off frequency ?
Best regards

[Sean]

The input circuit shown in the previous post feeds directly into the non-inverting input of the op-amp.

The op-amp is configured as a simple voltage follower (unity gain, no additional filter).

[icare34]

Hello,
The Miac module is very well done (compact, small keyboard, display, lots of I/O ..).
Flowcode is a very good graphics sofware for programming PIC.
But I have problem, for my application, with I/O -> 3 solutions for me :

• create and use a extra module to adapt level, cut-off frequency to the Miac Module -> not good for the final user (more external connections ..)
• Replace the Miac I/O board by a another one -> not very easy with no technical information
• Find an other product

So, is-it possible to have shematic and PCB technical data of the I/O board ? Other solution ?
Best regards

[Benj]

Hello,

We are currently working on a set of CAN based expansion modules for the MIAC that should hopefully be available around the end of next month.

Otherwise you can always connect multiple MIACs to a CAN bus and get more outputs this way.

[icare34]

Thank you
One or 2 months is not a problem for me.
My problem is not the number of analog input (1 need 3 analog input in my application), but the range (in V) and the filtering.
It's a noisy electrical environnement, I need to respect Shannon condition : so I need to use filter before digital conversion.
I have 2 solutions :

• Use 3 FIR filter -> not easy to implément in the software
• Use hard low pass filter : ...

Are the new "CAN based expansion modules" going to resolve my problem ?
Best regards

[Sean]

The 12V conversion range of the MIAC ADC is a fundamental requirement of the device spoecification. The I/O on the expansion modules will operate over the normal 5V logic range.

We can not release the full schematics for the MIAC, but the details included in previous posts provide a complete description of the circuitry associated with each input - with the exception of some protection components that should not affect voltage or frequency range while inactive:

Terminal -> Potential divider with capacitor -> Buffer op-amp -> PIC.

[icare34]

Hello,
Is the" I/O on the expansion modules" have been developped ?
Where can I see them ?
Best regards

[Benj]

Hello,

The MIAC expansion modules are currently in development and will be arriving shortly. Sorry I cannot really give any more solid information at the moment. Hopefully within the next month or so we will have a release or at least a better idea of release dates.