Fish Finder Depth Sensor

Sadly we did not win one of the five Volta Cohort investments last week, but it was still a valuable experience nonetheless. We were able to practice refining our pitch and improve the focus of the business, which should help us going forward.

The next couple of days were spent writing driver software and hooking up cables to convert the RS-232 output from the fish finder into depth measurements for AMOS's Raspberry Pi. I bought a 3 foot long RS-232 to USB cable for this purpose, but couldn't find the male DB-9 plug for soldering that I thought I had lying around somewhere. So  I snipped the cable near the end and pulled out the bare circuit board inside:

This afforded some better soldering points for the white, green, and black wires on the top surface of the board. And as luck would have it, I didn't mix up the green and white TX/RX cables.

The fish finder outputs NMEA 0183 sentences in ASCII text at 4800 bps, something like this:

$INDPT,1.1,0.0*47
$INHDG,,,V,,V*60
$INHDT,,T*0B
$INGLL,,,,,,V*16
$INVTG,,T,,M,,N,,K*5E
$INMTW,10.1,C*14
$PSMT,0,0,0,2,appver,0*28
$INDPT,1.1,0.0*47
$INHDG,,,V,,V*60
$INHDT,,T*0B
$INRMC,,V,,,,,,,,,*21
$PSMT,0,0,0,2,appver,0*28
$INDPT,1.1,0.0*47
$INHDG,,,V,,V*60
$INHDT,,T*0B

The lines that matter are the ones that start with either $INDPT or $INMTW. These correspond to either depth or temperature respectively. Fortunately there are lots of websites around that summarize what the NMEA sentences mean, so I didn't need to pay $1000 or more for the official standard. Writing the software driver for the Pi to parse this info was pretty straightforward. Just needed to make sure that the software polled the serial port frequently enough to keep the depth data current. Depth is sent out only once per second by the device, so it's not exactly a compute-intensive task.

On Sunday Kirsten and I took advantage of some good weather to take the canoe and AMOS out for a test. Unfortunately AMOS kept veering off to the left for no known reason. A later inspection back at the house indicated that one of the electronic compass wires had come unplugged. The following day I tried again, but the same thing happened, it kept trying to go west when it should have been going north. Wanting to test the fish finder anyway, I towed AMOS around in the kayak for about an hour. I didn't cover quite as much water as I thought I did, but the results for the depth measurements were pretty good:

and with interpolation turned on:

That evening I checked the compass calibration on the grass in our backward and found that it was indeed off by about 90 degrees, i.e. when the boat was pointed north the compass output indicated that it was facing east. I'm not sure yet if this is some new hardware problem, or if the compass calibration got messed up somehow and needs to be re-calibrated. Hopefully that'll get solved tomorrow.

AMOS Featured in the MagPi

Merry Christmas / Happy Holidays!

I was planning on taking this week off from the blog, but just discovered this evening that AMOS appeared in the January 2020 edition of the MagPi: https://magpi.raspberrypi.org/issues/89/pdf. This is the official Raspberry Pi magazine. So definitely pretty cool, and worth bragging about! 😊

The magazine edition can be downloaded for free from the above link, but here are some screen captures of parts of it:

First Products and SEO

As mentioned previously, the vital parts of AMOS will be released as products in their own right in the coming months, leading up to the release of the entire robot in the summer of 2020. The first of these was the waterproof housing that was built for the Raspberry Pi camera that AMOS uses:

This product was called the WeatherBox, and a link to its store location can be found here: https://www.innaturerobotics.com/product-page/weatherbox-for-raspberry-pi-camera-v2 This product was actually split into two different models, one with the Raspberry Pi v2 camera and cable included (WeatherBox-CAM) and one without.

The second was the 16-bit, variable gain A to D board that was described last week. It was populated with all of the necessary components, and all four channels and gain settings were successfully tested out with a little Arduino program and circuit that I made for that purpose:

This one was called the ADS1115-BRVG and its product page can be found here: https://www.innaturerobotics.com/product-page/ads1115-variable-gainboard.

Since the website's SEO (Search Engine Optimization) is still sub-optimal, I'm reading some tutorials on how to get your webpage to show up higher in search page rankings. Apparently there is something like 200 different parameters that Google considers in these rankings. Right now I'm just starting out; trying to make sure all the pages on the website have suitable titles and descriptive text. One thing that was encouraging today, was that when I searched for "nature robotics" with the quotation marks on Google, www.innaturerobotics.com was the first link. Without the quotation marks, it was on page 2, 14th place overall. Those high rankings are probably biased by my location however, as I read that Google ranks local businesses higher.

This coming week I would like to try some calibration experiments on the IMU (Inertial Measurement Unit) and current draw sensor. I suspect that both of these are affected somewhat by temperature, so I'll try heating them up in a box and then put them outside to cool slowly for an hour or two, to see how the outputs change. The magnetometers on the IMU should also be calibrated more carefully than what I did previously by hand. Probably a motor turning apparatus, similar to what I have used before at Measurand would work well.