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Geo Brick Drive Analog I/O
#1
I'm currently trying to configure the analog I/O options (connector X9) on a Geo Brick controller and I'm running into a few difficulties.

The device connected to the input provides a single ended unipolar signal (0-10V), and I've verified that it is working with a volt meter.

The device connected to the output expects a single ended bipolar signal (+/- 10V)

I've configured the I variables and M variables to the recommended settings on pages 150-152 of the Geo Brick manual (the controller is currently at factory default configuration, except for the recommended I/O configuration settings), and I got the following results:

The analog output seems to work, except that when pin 7 is tied to AGND as shown in the Single Ended wiring diagram on page 151, the output saturates at about +/- 4.2 V instead of +/- 10V. It seems to be linear and correctly scaled up to that point, but won't go any higher. With pin 7 disconnected, I can get the full +/- 10V range (measured between Pin 3 and AGND). Is it alright to just leave pin 7 disconnected?

Also, the output is 12-bit, so it should have a range of 4096 counts, but the default settings restrict it to +/- 816 (1633 counts). If I'm understanding the documentation correctly, this limit is based on the PWM frequency configured by I7100. Based on the requirement that PWM frequency should be a multiple of (Phase frequency/2), it seems like I7100=2175 would be the closest to the +/-2048 needed to get the full 12-bit resolution. This would put the PWM frequency at 13.55 KHz (4.5173 KHz * 3), which is significantly below the 30-36 KHz range recommended. Is this reduction in frequency likely to cause serious ripple problems, possibly negating any benefits of the increased resolution?

I'm having problems getting any reading at all from the analog input. With the suggested configuration on page 150, M505 always reads -1, and it does not change at all (not even a few counts of noise that might be expected if nothing was connected). Is there something else that needs to be configured to read these inputs?

Thanks,
Tim Drumheller
#2
FYI, I don't think you are looking at the latest revision of the Brick Controller Manual (Here is a link to the website version).

Regarding the Analog Output:
It is ok to leave Pin#7 floating, as long as you are getting the desired signal out. This might be a documentation mistake. Let us take a look at it.

Yes, the reduction in frequency causes more ripples thus defeating the increased resolution. It is a trade off.

Regarding the Analog Input:
Make sure that servo IC1 ADC Strobe word is set to $1FFFFF. Otherwise, it will show a -1 if the option is not there/installed.


#3
I'm using the Geo Brick Drive (with built-in amplifiers), not the Brick Controller. The page numbers I was referring to were from the October 13, 2011 version of the manual, and it looks like there was a new version of the manual on April 15 that moved the relevant section to pages 138-140, but the information seems to be the same.

The suggested configuration (page 138, formerly page 150) that I used for the analog input is:

M505->Y:$078105,8,16,S ; ADC Input value (ADC5A)
M605->Y:$07810D,8,16,S ; ADC Input value (ADC6A)
M705->Y:$078115,8,16,S ; ADC Input value (ADC7A)
M805->Y:$07811D,8,16,S ; ADC Input value (ADC8A)
I7106=$1FFFFF ; Servo IC1 ADC Strobe Word
#4
What are the serial and part numbers of your unit?
#5
Serial#: C000A4KE
Part#: GBL4-F3-800-13D00000

Thanks,
Tim
#6
Ok, it looks like you have the 2 x 16-bit analog inputs (at connectors X11, and X12).
Now, if you do a $$$***, set I7106=$1FFFFF and download the suggested M-Variables. You should see M705, and M805 (in the watch window) floating about zero if nothing is connected.


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