raspberrypi expansion module

Request new hardware or ideas for the controller

Posts: 12455
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Tue Feb 19, 2013 9:15 am
If you are trying to have a Pi module that replicates the wifi attachment, you need to make it as the Pi is a Serial to TCP converter.
Roberto.

Posts: 293
Joined: Tue Oct 25, 2011 7:39 am
PostPosted: Wed Apr 03, 2013 3:21 pm
I too have been looking at the Pi... in terms of replacing the RA processor with the Pi- big issue is PWM output ... Pi has only 1 channel although there are some work arounds for this in software https://projects.drogon.net/software-pw ... pberry-pi/ but it eats clock cycles and of course uses up the other output pins... I believe I found a hardware (USB maybe) board that can interface for multi channel PWM ouput on the Pi but now its two pieces of hardware.. Would be nice to have something with enough PWM channels and outputs for everything else in 1 box... with internet!
Gotta love the memory though.

Posts: 13
Joined: Fri Oct 05, 2012 11:01 am
PostPosted: Thu Apr 04, 2013 1:08 pm
rufessor wrote:I too have been looking at the Pi... in terms of replacing the RA processor with the Pi- big issue is PWM output ... Pi has only 1 channel although there are some work arounds for this in software https://projects.drogon.net/software-pw ... pberry-pi/ but it eats clock cycles and of course uses up the other output pins... I believe I found a hardware (USB maybe) board that can interface for multi channel PWM ouput on the Pi but now its two pieces of hardware.. Would be nice to have something with enough PWM channels and outputs for everything else in 1 box... with internet!
Gotta love the memory though.


How about this add-on chip. Adds 16 PWM channels should be more than enough.

http://www.adafruit.com/products/815

Posts: 12455
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Sun Apr 14, 2013 9:28 am
Take a look at these:
http://www.youtube.com/watch?v=F-te4qkbh28
http://www.doctormonk.com/2012/04/raspb ... duino.html
The first one show the Arduino IDE running on the Pi and the 2nd one shows how we can leverage the wifi framework we already have and use Pi as a internet bridge.
We just need a python script, I guess... :)
Who know python really well?
Roberto.

Posts: 12455
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Sat Apr 20, 2013 9:27 am
Ok, so I got my PI a couple days ago and here is what I got so far :)
http://i761.photobucket.com/albums/xx25 ... cb4643.jpg
Roberto.

Posts: 33
Joined: Thu Sep 20, 2012 2:34 am
PostPosted: Wed Apr 24, 2013 3:23 pm
cypho wrote:
How about this add-on chip. Adds 16 PWM channels should be more than enough.

http://www.adafruit.com/products/815


Yep, those do work fine with the Pi. I have 2 of those hooked up to mine along with 2 x 16 bit GPIO, 1 x 12 bit 4 Channel ADC and 2 x 12 bit DAC for my 2 (soon to be controlled) WP40s. At some point the Pi will be hooked to the RA.

Which brings me to the reason I stopped by. I built an ATO/AWC with 4 water level sensors using the MPXV5004G chip. I noticed that the sensor in the sump seems to drift higher by 4% over a couple of days. If I lift the sensor from the water exposing it to the air, once submerged, the reading becomes accurate again. At first I though I had a leak that was allowing the water level to rise in my tube, but after thinking about it, that would cause the reading to be high, not low.

I am now leaning toward changes in barometeric pressure between when the sensor is lifted, and reset to ambient pressure, and when the ambient pressure changes over the course of a few days.

Is anyone using the RA version of the water level sensor seeing anything similar, and does the RA version take into account the ambient pressure at the time of calibration?

I am probably over thinking this. :?

Dennis

Posts: 137
Joined: Sat Feb 16, 2013 7:44 am
PostPosted: Wed Apr 24, 2013 3:36 pm
Actually I think it could be an air leak. If you sensor is reading a higher water level, I think that means the air pressure exerted on the sensor by the water pressure would lower which should result in a higher water level. If you can use a clear plastic tube and see if water is climbing into the tube... It really shouldn't happen very much.

Posts: 33
Joined: Thu Sep 20, 2012 2:34 am
PostPosted: Wed Apr 24, 2013 3:53 pm
That was my first thought as well. But the sensor is reading a lower reading after a few days when the water level is at the target. Unfortunately the sensor tube is CPVC, so it is opaque. I re-cut the end of the PVC hose that connects through a Watts connector to the sensor tube this morning, so we will see if it has any effect in a few days.

I am concerned as I don't want my AWC to increase the salinity over time.

The other long shot I was thinking of is micro bubbles that are traversing the baffle where the sensor is adding to the trapped air in the sensor tube. This seems like a very remote explanation though.

Dennis

Posts: 33
Joined: Thu Sep 20, 2012 2:34 am
PostPosted: Wed Apr 24, 2013 4:33 pm
Actually I think I described it wrong. The sensor is reading higher, but the actual water level at that point is lower. So it is reading more pressure in the sensor tube then the water level would normally exert.

Dennis

Posts: 12455
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Fri Apr 26, 2013 3:21 pm
Wow... That was not easy... lol
But I finally got the Arduino IDE to compile our libraries.
I just didn't upload to test it yet...
The weird thing is that the compile size is very different...
Windows:
Binary sketch size: 42,588 bytes (of a 258,048 byte maximum)

Pi:
Binary sketch size: 40,464 bytes (of a 258,048 byte maximum)
Roberto.
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