AI Cat Deterrent Automatic Sprayer

So I'm coming back to this project after a long time away from it and trying to remember where I left off. I have a semi-functional GUI, a very slow camera feed from my Raspberry Pi Zero W, and what is hopefully the final iteration of a PCB to make it all work. I do remember that the second slide switch to power on the board wasn't rated to handle the power that I'm using, so the contacts fused together when I switched it on. I've since replaced that switch with a much bigger one that I hope to build into a 3D printed enclosure. Stay tuned for more updates as I actually make progress towards this again.

I ordered in some replacement parts for both of the issues mentioned in the previous log.

First, I replaced the relay with a darlington pair BJT. This offers absurdly high current gains for very low Base currents. In other words, it will work to power my windshield washer motor, which needs around 2.5A to function, with the < 16mA I get from the RPi gpio. In the attached breadboard picture, I have a test setup for this.

Second, I replaced the 5V LDO with a 5V switching regulator. I ordered two just to be safe (lm2576-5.0WT and bd9874cp-v532), which also allows me the flexibility of putting these regulators in series if they still get too hot. After leaving this circuit to run for a few minutes, there was virtually no heat coming from the regulator. We'll count that as a win!

As I mentioned earlier, the attached picture is from the component testing I did on my breadboard. After confirming these components are good solutions, I went back and did my board design for v3 of this project. My schematic and Layout are now as follows.

The first version of this board has two major issues that inhibit the hardware functionality of this project.

First, the relay mechanism doesn't work to switch on the sprayer when excited by the gpio pin. On further research, it looks like a Raspberry Pi Zero W can only source about 16mA of current. This relay needs 50+mA to latch, making this concept inadequate for our feline spraying needs.

Second, the 5V LDO gets roughly as hot as the surface of the sun because I'm trying to drop as much as 14W across it. Since I'm not keen on giving up my security deposit, it would be good to switch this out for another option that's less likely to start a fire. According to various sources online, a switching regulator is better in this arena as it won't get so hot.