I’d just buy this guys device . Based on Rasberrypi too.
https://www.reef2reef.com/threads/announcement-my-own-builded-kh-machine-is-ready.278352/page-32
Nothing stopping you from doing that. Personally, I like that and the Apex systems best. Apex is out because I just got the older system and I'm not paying for their Alk monitor and upgrading half my system. Reeftronics looks nice but I like an adventure
Great stuff.
Looks overall good to me. My advice will be not to spend a lot of time in getting the perfect circuit done. Whatever you build, it will likely go through multiple iterations before things settle down. I suspect a lot of it will involve having different calibration and validations in place.
I would consider a dual h-bridge darlington driver like l293d to drive the stepper or dc motor based peristaltic pumps. I am not sure how accurate is drop count via IR sensors, give it a shot. Using the peristaltic pump to pour measured amount is a common use, and we know that route will work, in fact some of the vendors (like atlas scientific) provide I2C interface specificallt geared towards that, just something to note.
I would also suggest using Pi over arduino. This will significantly reduce your development/iteration cycle time. Its cheaper (zero w is only 10$), and unless you need an analog input, you will have everything that you need (including two hardware backed pwm pins). Even for bare minimal testing, you 'll need to chart/analyze multiple readings, Pi and the entire linux ecosystem (python for example) will come very handy.
It will be very helpful if you keep the software under apache 2 or MIT and the hardware under openhardware licensing, that gives us (reef-pi and similar projects) an easy way to integrate with your project as well as vendor can consider this for their products without worrying for royalty. Its not a must, just a nice to have.
I have pondered about integrating a general titration module using ph/color sensors along side peristaltic pumps for reef-pi. But our current priorities are around 2.0 milestones, I hope we'll get back to this early next year or after x-mas. I hope we'll be able to use your learnings/project.
Godspeed & keep us posted. Any help I can offer around electronics/software/Pi let me know.
Thanks Ranjib, appreciate looking over my first chunks of work so far, I have been following reefPi here for a while now and love what you are doing with it. Happy to work on integration with both projects sometime for sure.
I will look into the H-bridge. Certainly not an engineer so might take a while to figure out why I would need them but the main key is that I can control the speed. The calibration plan right now is to figure out the fastest speed where the IR can accurately count drops but also not take forever to perform a test. This also would allow people to essentially use any decent pump with the system automatically adjusting.
I went the Arduino(ish) route just because it's easier for me to prototype with, honestly. The Particle Photon board has benefits over the normal Arduino which just adds to that (i.e. remote flashing). I know I will probably switch to something else eventually but for now I like the simplicity of the Arduino platform.
I'm not too worried about the software side license yet but thanks for the tip there. Certainly going to keep this open and make it easy for others to use, just don't want anyone profiting off of it really.
Right now I really like the idea of using a BNC for the output so essentially any controller can read the output. I am also going to try and keep the API open so the web based tools could be used separately as well. No idea yet if it makes sense to support other specific controller connections yet.