This is an update on my progress in creating a sensor for my thesis project, in the form of a PCB board based on the Human Presence Sensor from Sparkfun.
The goal is to hide the sensor as part of the structure of a leaf on an installation (my thesis) that consists of robotic branches. The sensor will go in the front most leaf, pointing towards the audience. The sensor will control the movements of the robot. So if a person moves too fast, the branch will hurt and start hanging down.
This is what the sensor looks like from Sparkfun.
I have been doing tests with the sensor for a while:
In order to re-design the board I followed this guide from the class website http://homemadehardware.com/guides/redesign-online-circuits/.
My goal is to not have a single via. As I am creating a single sided board and that has the aesthetics of a leaf.
My files are here on Github: https://github.com/louiselessel/HomemadeHardware_git/tree/master/AK9753_Human_Movement_Sensor_To_Leaf
This is the board as it was downloaded from https://learn.sparkfun.com/tutorials/qwiic-human-presence-sensor-ak9753-hookup-guide
This is the board after I removed unnecessary elements (I removed everything that is listed as optional on the Sparkfun page + the connectors). But before cleaning up the file.
I removed the following:
[About JP7] …There are several jumpers on board that can be changed to facilitate several different functions. The first of which is the I2C pull-up jumper, highlighted below. If multiple sensors are connected to the I2C bus with the pull-up resistors enabled, the parallel equivalent resistance will create too strong of a pull-up for the bus to operate correctly. As a general rule of thumb, disable all but one pair of pull-up resistors if multiple devices are connected to the bus. If you need to disconnect the pull up resistors they can be removed by removing the solder from this jumper.– Sparkfun
I then proceeded to setup the DRC, though I can tell from my AK9753 part that my routes settings in this might be too wide.
I can also see that there might be electrical issues with the board, but I am not sure why they are issues yet.
Then I cleaned the file from extra information and performed ripups on both sides of the board (ripup *)
Then I moved things out of the way to get an overview to start rearranging. And I looked at the schematic. I am guessing here, but we have used a capacitor before to remove noise when it is close to the voltage pin on a microcontroller, and I can tell from this .sch file that the capacitor is drawn next to the AK9753, so probably I should keep it close.
I then started moving things around and getting an overview over what went where. A nice thing about Sparkfun is that the have labels on each ends even on the resistors! This makes it a lot easier to see. Also, I should have used ratsnest a lot more here.
Then I started actually arranging and laying down a basic version. I found that I need to swap the ground and interrupt pin, to make everything happen without any vias.
As is evident I need to make the routes thinner, and prepare the board for acid etching rather than the Bantam. I need to find a connection that is used for flexible PCB (ask Andy).
I also need to arrange everything in the shape of leaf veins like this, by following the guide (http://homemadehardware.com/guides/eagle-board-design-1/ ):
I researched more into making the acid etching (http://homemadehardware.com/guides/acid-etching/) from home, and while that is the look I want it will not be possible to do right now, because I do not have access to a printer, the vinyl or the chemicals.
However I did prepare the board for the acid etching, meaning that I made all of the routes thinner. I read in the Design Rule (DRC) the comes with EAGLE when you downloaded it, after advice from Andy. A major change I did is to swap the header pins for simple test pads, so I can solder the wires directly on.
Then I started laying out the board in the shape of a leaf. Here is my first attempt, which was way to big – The bottom part of the leaf stem is 9 mm across, and the branch this will be mounted on is only 20 mm wide. So I redrew it, so the leaf is 65 mm across.
I used the line tool on the Dimension layer, and set the line type to the Snake-like setting in the top menu. I followed this guide (http://homemadehardware.com/guides/eagle-board-design-1/).
After drawing the shape it was just a matter of laying out the parts so they would make up the veins of the leaf.
I added a flat part in the bottom, so I can make a small corresponding cavity inside my branch, that can keep it in place. Then the stem can come out of a narrow slow. I did not put holes in, because I can punch holes in the acid etched board after.
- 2 x 1.0 uF capacitor
- 2 x 4.7 kOhm resistor
- 1 x 330 Ohm resistor
- 1 x 10 kOhm resistor
- 1 x AK9753 $5.18 – $11.60 (https://www.digikey.com/product-detail/en/akm-semiconductor-inc/AK9753AE/974-1157-2-ND/7388309)
- 1 x 6×6 inch thin flexible pcb sheet $15.99 (https://www.amazon.com/gp/product/B076C41MTV/)
Here is the final schematic:
The leaf will go on the front of this branch (this is a prototype). The movement will be similar to the Mimosa Pudica. I am still working on this part though:
This is what it looks like if I were to mill it on the Bantam Othermill. This look is also very cool. Perhaps for another project. Because I did get very inspired when I learned I could do silver coating (http://homemadehardware.com/guides/coating/). I really do love the fine arts look these can get.
Everything is on the GitHub I linked in the top of the post, but here are the PDF Schematic and Board.
The final look I am going for with the acid etching is this, but with silver or cobbler veins: