Register a SA Forums Account here!
JOINING THE SA FORUMS WILL REMOVE THIS BIG AD, THE ANNOYING UNDERLINED ADS, AND STUPID INTERSTITIAL ADS!!!

You can: log in, read the tech support FAQ, or request your lost password. This dumb message (and those ads) will appear on every screen until you register! Get rid of this crap by registering your own SA Forums Account and joining roughly 150,000 Goons, for the one-time price of $9.95! We charge money because it costs us money per month for bills, and since we don't believe in showing ads to our users, we try to make the money back through forum registrations.
 
  • Post
  • Reply
kid sinister
Nov 16, 2002

LimaBiker posted:

Smell? Quite hard.

Actual temperature? Much easier with an infrared thermometer pointed at the spot where the engine will most likely be. Thermal imaging if you wanna be real fancy.

Seconding infrared. You might want to point it at the back of the cars to pick up the tailpipes.

Adbot
ADBOT LOVES YOU

ryanrs
Jul 12, 2011

So it's not even a running engine, just the smell of hot metal and grease and such? Detecting that by smell is a science project that is much more involved than running a wire, imo.

Skinnymansbeerbelly
Apr 1, 2010

Shame Boy posted:

You'd need to know what kind of vapors that smell is made of first, but there's plenty of sensors that can detect basic molecules like CO concentration or volatile organic compounds or something like that that might work :shrug:

Yeah I already tried with an SGP-41, it was a complete failure :v:

Also, is there an underlying reason that the narrow FoV IR thermometers are so loving expensive? Even one dimensional ones are $40

Splode
Jun 18, 2013

put some clothes on you little freak

Shame Boy posted:

You'd need to know what kind of vapors that smell is made of first, but there's plenty of sensors that can detect basic molecules like CO concentration or volatile organic compounds or something like that that might work :shrug:

Or just like, sense the car using an electric eye sensor or whatever and then start a timer to run for an hour.

Yeah surely the easiest way is to just detect the car itself. When the car arrives, start a timer and turn it off after that.

To detect a car you could use a distance sensor of any kind (IR reflective, IR beam break, ultrasonic, you name it), or something in the car (eg some kind of transponder, or an RFID tag - you can get systems that operate at a reasonable distance).

You could also detect the state of the garage door using a similarly wide number of options.

You could even detect yourself! Something like when your mobile joins the wifi, kick on the purifier for X time. This only works if you're only leaving via the car and only people who's phones you can ID are using the garage.

All of those are going to be way cheaper, more reliable, and ultimately simpler than trying to detect exhaust gasses. However, gas detection is dope so if you want to do it that way because it's cool then more power to you, and please continue posting about the project as it's a fun one!

Cojawfee
May 31, 2006
I think the US is dumb for not using Celsius

Skinnymansbeerbelly posted:

Yeah I already tried with an SGP-41, it was a complete failure :v:

Also, is there an underlying reason that the narrow FoV IR thermometers are so loving expensive? Even one dimensional ones are $40

The IR gun thermometers on amazon have gotten pretty cheap, one there is as low as 9 bucks. You might be able to break one of those open and hijack what it is doing.

ryanrs
Jul 12, 2011



Poop Alarm is starting to take form.

I'm going with a PLC-like design, because I've always wanted to build an electrical control panel with DIN rail and terminal blocks and relays.

Raspberry Pi Zero 2 W to run the show.
12V 3A step-down for beepers and misc HMI devices.
5V 5A step-down for the Pi Zero a power-hungry USB peripheral.
4x PLC-style digital inputs.
7x low-side outputs, 500 mA/ch. Good for driving relay coils.
4-channel leak sensor (simplified design from previous post).
RF module, receiver for keyfob remote.

There's a lot more I/O than I need. But I figure once I have a controller in the garage, I'll find other things for it to do.

Control engineers: Do PLCs count their inputs and outputs starting from 0 or 1? I feel like I've seen both, and I'm wondering if one convention is dominant, or if it's just random based on manufacturer and history.

ryanrs
Jul 12, 2011

Poop Alarm?
Sewer Sentry?
Brown Alert?

kid sinister
Nov 16, 2002

ryanrs posted:

Poop Alarm?
Sewer Sentry?
Brown Alert?

Number 2.0

Stack Machine
Mar 6, 2016

I can see through time!
Fun Shoe
Stool Tool

kid sinister
Nov 16, 2002
Potty Spotter

csammis
Aug 26, 2003

Mental Institution
Brown-out Detector

hark
May 10, 2023

I'm sleep
Might work better with an arduduino

some kinda jackal
Feb 25, 2003

 
 
espp32

Adbot
ADBOT LOVES YOU

ryanrs
Jul 12, 2011



Changes:

I put the Raspberry Pi Zero on the wrong side of the board. It needs to be aligned with the right edge so that the microSD slot is accessible on the left side. This board will be mounted on a DIN rail, so there will likely be tall modules on both sides blocking access. Only the top and bottom edges are open.

The Pi Zero will be plugged in face-down, because that's how the standard GPIO header is placed. Pi HATs are supposed to be small and mounted on top of the Pi. But upside-down mounting should be fine. The USB and HDMI ports will still be visible, because they stick out a little beyond the edge of the Pi. But the microSD slot will be completely hidden, and it'll probably be annoying trying to insert the card. So I drew a little picture to help you find the slot.

Moving the Pi to the right side evicted the RF module. I'll hand-solder it to the back of the pcb, which is probably a quieter location for it anyway.

Renumbered the I/O starting from zero. It really does seem to vary by PLC brand.

Replaced the 500 mA darlington low-side driver with discrete SOT-23 MOSFETs. Turns out that chip's 500 mA rating was largely aspirational. It could probably drive my seven 24V industrial relays just fine, esp at room temperature. But if you tried to drive several 12V automotive relays, it could overheat. I felt it was under-powered for what should be a bank of general-purpose outputs.


I replaced it with a 74HCT244 to boost my 3.3V logic to 5V gate drive for a bunch of 0.12 ohm MOSFETs. Low Rdson means you never have to give a poo poo about coil current or duty cycle.

e: Am I supposed to fuse these outputs? I don't think a polyswitch is fast enough to save a SOT-23. I see electricians talking about fusing PLC outputs, implying that the PLCs don't have internal protection, maybe.

OTOH, with 7 outputs, I can tolerate some attrition. Ablative circuit protection lmao.

e2: I think a 1.25 A polyswitch should melt before this 0.036 ohm MOSFET. I think that combo should be able to short out a big 24V supply and live to switch again (maybe). Probably worth the extra $3 for reliability in the face of wiring mistakes.

ryanrs fucked around with this message at 06:01 on Mar 28, 2024

  • 1
  • 2
  • 3
  • 4
  • 5
  • Post
  • Reply