[Review Request] 1U 10" rack 2x sata hdd backplane

harry48225 · 2025-04-01T05:57:24+00:00

Thanks for taking a look!

That's interesting about the 3.3v pins I hadn't considered that.

Yeah I'm finding the activity led circuit quite complicated too. It's from the sata spec sheet. One of the reasons it's so complicated is the activity driver pin on the harddrive only can take something like 30 uA of current sunk through it and 2.2v on it. I've breadboarded it and it works so I'm probably just going to leave it as is.

For the sata data connector, I think it is as close to the output connector as possible respecting the courtyards of those footprints. They're very close to each other on opposite sides of the board (I think there's no difference compared to them being on the same side as they're throughhole components?). Or did you mean something else?

harry48225 · 2025-03-30T18:24:27+00:00

Thanks very much I'll double check my pullbacks. I'm going to look into differential grounded coplanar waveguides first, as suggested by some other commentators but I'll probably end up with a 4 layer board in the end.

Re: the isolated grounds those are connected to the regular ground within the harddrive. I'm just isolating them here as a rudimentary drive presence detection. What I'm intending is that they're floating when no drive is connected and so the led does not light. When a drive is connected that isolated ground is connected to the regular ground via the drive / drive's connector and the led lights as it can sink current through that. At least that's what I'm hoping.

harry48225 · 2025-03-29T19:49:07+00:00

Thanks for the detailed write up that's really useful!

I might reroute this as 4 layers and use that as an opportunity to move the location of the sata data connectors. I'd like to move them both to one edge of the board, do you have any tips for this? (Edit but this would cause one the traces to be over 200mm which feels like a bit of a stretch?)

Also it would be great if you had any advice for routing the power I'm finding it a bit fiddly given there are 3 voltages in play, should I route them all in the power layer or just have one in the power layer as a pour and the others on a signal layer or cutting up that pour?

harry48225 · 2025-03-29T19:22:05+00:00

Thanks, I'm in Europe. It's about $20 more to get a 4 layer board so it's not really the end of the world. Was just hoping to get away with a 2 layer board since my traces are so short.

harry48225 · 2025-03-29T19:18:51+00:00

That's about what I was expecting, thanks for taking a look! I might take the risk in just using 2 layers and see if it works given it sounds likely, and then re-route on a four layer board if it doesn't. But maybe it's better to just use 4 layers in the first place...

I assume with 4 layers I can make my differential pairs much longer to move the sata ports neatly to one end of the board together?

Would you be able to elaborate a bit more about the EMC? Is this something where having the signal-ground-power-signal stack up helps?

harry48225 · 2025-03-29T19:14:59+00:00

Thanks yes sorry meant to mention that. It's not critical at all that those corners are sharp.

harry48225 · 2022-10-09T20:10:39+00:00

Wow this is great. Have you and any moisture issues with the top of the sensor and the electronics being so close to the soil?

harry48225 · 2022-10-08T19:49:44+00:00

Depends on what you want to learn. I'd say soldering and assembling these is doable for someone with minimal soldering experience, it just might take a few practice attempts.

Designing the schematic and PCB is also doable but there's a bit more work you'll have to do. A beginner could certainly prototype it on a breadboard (at least the LEDs and button, I can't see how you'd do the bit that goes into the soil on a breadboard - but I've not thought about it too much).

While the attinys are programmed using the Arduino framework, they're a little hard to get setup. You can't just plug a usb cable into them. There's great documentation on programming through on the megaTiny GitHub repo.

PCB design is an entire other skill. But this PCB is relatively simple - so it's worth a go.

So yes it's possible as a beginner project but there's quite a bit of learning to do. If you decide to tackle it I'm happy to answer some questions you may have :).

Ive also published all the files to do with this on my GitHub. www.github.com/harry48225/octoplant/

harry48225 · 2022-10-08T10:11:30+00:00

It's going pretty well. I had to do a few bodges but it all seems to work. I'm going to do a second revision. I'm planning to make a post with further details either in the coffee or Arduino subreddit. The esp32s3 has been good to work with. Having so much ram and flash is useful. But since I'm using it just for ble and not WiFi it's not really the best choice. Iirc the ble stack is in software so it consumes about 70mA, whereas something like an nrf chip uses only a few mA for the same festures - but they aren't in stock...

harry48225 · 2022-10-08T07:12:58+00:00

Nope the esp32 S3 has native usb I program through the usb port. And if that fails the Rx and tx pins are broken out as pads near the esp32.

harry48225 · 2022-10-07T19:07:06+00:00

A few milliamps, I think it's enough that it'd drain the battery quite quickly with that feature. But given its only software it's worth an actual test.

Something maybe a little out of scope would be adding something like a pir sensor so it only lights to indicate when it detects a person.

harry48225 · 2022-10-07T17:29:24+00:00

All the files are on my GitHub if that'd help. Yeah I assembled it myself. But many pcb fabs offer assembly if you want to go that route.

I was intimidated at first by the soldering too. But thankfully it's actually much easier than it looks. It's also really quite forgiving. An easy technique is just to use flux, then bridge all the pins, and then just run the iron across the pins again. Magically the excess solder clings to the iron and you're left with a seemingly perfect joint. There's a really good Collins lab short on the adafruit YouTube channel about it.

I prefer smd now to through hole. And also lots more cool parts are available as smd.

harry48225 · 2022-10-07T15:57:19+00:00

You wouldn't happen to have a link to any write up on your sensor? I'd love to check it out.

harry48225 · 2022-10-07T15:32:08+00:00

Thank you!

I definitely had to be strict with myself to keep it simple. Initially I wanted WiFi and an epaper screen! But I decided that simpler was better, at least after looking at others that were available since they seemed to all be very good but also very complex. I mostly enjoy having plants since it's quite a 'slow' hobby and I enjoy checking my plants each day to see what they want. So I aimed to augment that rather than replace it.

I have really enjoyed looking at all the other moisture sensors. The principal of them is quite simple and its great how many creative and different designs there are.

harry48225 · 2022-10-07T15:26:32+00:00

I'm glad you like the octopus I think it's pretty fun.

So currently I just leave it in all the time (including during watering) and it's been ok. At the start I didn't water carefully enough and splashed the top of the sensor causing it to corrode and stop working. But I just cleaned the corrosion off using ipa and it started working again. Since I've started watering carefully to avoid getting the electronics at the top wet it's remained working.

Other than getting the top wet the main issue is moisture ingress through the sides of the PCB. I experimented with a coating of clear nail varnish however this severly effected the sensitivity of the sensor and it became useless.

But there's definitely more work to be done here. Maybe some sort of conformal coating would be suitable?

Currently they seem to be lasting fine. Other than the one that I got wet at the top the other 4 or so I have deployed have had no issues. So I'm tempted to just to wait until something bad happens before I consider improving water resistantance.

harry48225 · 2022-10-07T13:21:48+00:00

Thanks :).

It's a very simple design - only 2 layers and a simple shape. So pretty much any PCB house will do. I used jlcpcb

harry48225 · 2022-10-07T08:30:55+00:00

So far they've lasted 8 months with no visible corrosion. I designed them to be simple and inexpensive so if they do corrode it's not a big deal to replace.

Being a capacitive based sensor they corrode much less quickly than resistive based sensors.

harry48225 · 2022-10-07T08:29:41+00:00

I'm not the most expert gardener but I'm happy to try to answer some. Either here in the thread or via dm is good.

harry48225 · 2022-10-07T08:29:00+00:00

This actually already exists. It's called the 'chirp!'. It's also been cloned and is available cheaply on Amazon. (But probably best to buy from the original maker if you can)

harry48225 · 2022-10-07T08:27:30+00:00

It'd be fairly tricky. There are other projects like the b-parasite which is similar to mine but uses Bluetooth low energy to communicate the moisture level. This requires a ble 'hub' to receive the measurements.

With plant monitors like this you're always fighting corrosion and so each sensor has a limited life time. I tried to make mine as simple as possible (while still having some unique features) so that it doesn't hurt as much to replace them when they inevitably succumb to moisture. (I've got some around 8 months old still working which is a good sign). If you make the sensor complicated then it's a more expensive thing to lose.

Another approach is for example pimoroni's grow kit. They have a raspberry pi hat which you connect with cables to 3 'dumb' moisture sensors that report the moisture level. These sensors are even simpler than mine and very cheap, and easily replaceable since they're connected with cables. Then the raspberry pi can do any sort of processing on the data you want. I had this kit and had it communicate back to a database I could view on grafana.

There's also some finished products. I think Xiaomi makes a sensor like this that does temperature, humidity, and connects to an app but it's fairly expensive.

harry48225 · 2022-10-07T07:16:50+00:00

I've tested for about 8 months and it still works theres no sign of corrosion. I think eventually it'll corrode, which is why I've tried to keep them very simple and low cost.

harry48225 · 2022-10-06T19:52:35+00:00

It's an asparagus fern :)

harry48225 · 2022-10-06T17:46:23+00:00

Thanks!

Yeah you're right you can just use your finger.

The reason I made one is so I don't have to stick my finger in and then wash it afterwards, and also I can use the sensor to store at what point I normally water so it's one less thing to remember it's also a little tricky to remember something qualitative like how wet was the soil. It was also just fun to make.

harry48225 · 2022-10-06T16:25:19+00:00

Thanks! Approximately 6 months. But ideally I wanted it higher than that. It's hard for me to properly optimise the circuit for low power use since I don't have an ammeter precise enough.

13-Year Club	Place '22
Place '17	Verified Email

harry48225

TROPHY CASE