Advice needed on how to route air inlet and air outlet to a case.

[DrG]

Among my many "weaknesses", is the lack of ability to actually package a project. I am fine getting a project on a breadboard....and I have a whole bunch of filled breadboards to prove that point. To illustrate, I went looking for a breadboard and found at least seven around here, all populated. To my surprise, I even found one of a binary clock (pictured below) using a PIC16C54. I have a folder with the hand-drawn schematic and a printed code listing...dated 19-JUL-1993! Worked like a charm...still on the breadboard....more than 25 years later. Apparently, I am waiting for this historical artifact to be discovered by future generations where archeologists will debate its cultural significance.



This morning, I was going to drive out to a local place and buy another breadboard. This leads me, hopefully humorously so, to the point of my post. A while ago, I made a project to read and display particulate matter concentrations in air using **broken link removed** A close friend saw this project, which I demonstrated, and wants it to actually use in his shop. As he is a long time friend and colleague, I had it in mind to package it and send it along as a nice holiday gift. I can also reclaim the breadboard! I am asking for help.

So, here is the problem, the stumbling bock, the force that keeps it in place on the breadboard. If you look at the data sheet ( e.g., p4), you will see the air outlet and inlet areas that are used to pull the air sample in and expel it out. I am not finding a case that will exactly fit those dimensions and even if I could, I'm not sure that I could fit the rest of the components as well. I need to route those air ports to the case and I don't know what to use and how to attach them at either end. I want it to be both functional and neat. I just can't slop a bunch of glue onto some makeshift and ill-fitting tubes as it will look like a small child did it in 3rd grade art class.

How would you do it? Be as specific as you possibly can...where do I find square tubing for the exhaust fan and rectangular tubing to fit over the inlet (which is right on the edge of the sensor. What would I use to attach it to both the sensor and the case. How do I make a precision fit such that I could, at least potentially, get back into the project and reprogram as needed and so on?

 

[JimB]

Hmmm...
Not a very friendly thing for mechanically integrating into a standard case is it!

I guess when it was designed, they envisioned that it would either just sit inside an HVAC duct, or a custom plastic (?) case would be designed for it if used in a stand alone instrument.

In your case, my best suggestion is that the inlet port is butted up to one wall of the box, with a soft gasket between the wall of the box and the sensor to prevent air from within the box being pulled into the sensor.
At the outlet port, make a simple duct from sheet metal or plastic to guide the exhaust air to the side of to the box away from the inlet port.
Again some gasketing where the duct meets the sensor would be useful, but there does not appear to be much surface available due to the close proximity of the electrical connector.

JimB

 

[DrG]

Hmmm...
Not a very friendly thing for mechanically integrating into a standard case is it!

I guess when it was designed, they envisioned that it would either just sit inside an HVAC duct, or a custom plastic (?) case would be designed for it if used in a stand alone instrument.

In your case, my best suggestion is that the inlet port is butted up to one wall of the box, with a soft gasket between the wall of the box and the sensor to prevent air from within the box being pulled into the sensor.
At the outlet port, make a simple duct from sheet metal or plastic to guide the exhaust air to the side of to the box away from the inlet port.
Again some gasketing where the duct meets the sensor would be useful, but there does not appear to be much surface available due to the close proximity of the electrical connector.

JimB

Hmm that could work...I might even be able to make it work. Do hobby shops have "general" gaskets that I might play with? Do they still have "liquid gasket" (you know, gasket in a tube) - might that potentially work?

 

[rjenkinsgb]

Do hobby shops have "general" gaskets

You can buy neoprene foam sheet with a self-adhesive backing.

We use it to re-make the seals on machine tool control cabinets when replacing monitors and keyboards etc.

You can get multiple different thicknesses.
eg.
https://www.ebay.co.uk/itm/Neoprene...fing-Insulation-1m-x-900mm-x-4mm/253995904516
**broken link removed**

 

[DrG]

You can buy neoprene foam sheet with a self-adhesive backing.

We use it to re-make the seals on machine tool control cabinets when replacing monitors and keyboards etc.

You can get multiple different thicknesses.
eg.
https://www.ebay.co.uk/itm/Neoprene...fing-Insulation-1m-x-900mm-x-4mm/253995904516
**broken link removed**

Thanks much. I just came back from the hobby shop. They had no gaskets at all of any kind. They had some rolls (not very wide) of what looks to be exactly what you linked. Many years ago, I used something like that big (12"X12" squares) for sound proofing and I had completely forgotten about it!

Thinking along the same lines, I bought a sheet of this. The idea being that, as long as I can cut the inside diameter close to what I need, I can even double or triple layer them to get an appropriate spacing from the case. I also have some cyanoacrylate that has been rubberized or carbonized or some such thing.

I will post a pic if it works and looks like it was made by, at least, a 6th grader

 

[dknguyen]

Thanks much. I just came back from the hobby shop. They had no gaskets at all of any kind. They had some rolls (not very wide) of what looks to be exactly what you linked. Many years ago, I used something like that big (12"X12" squares) for sound proofing and I had completely forgotten about it!

Thinking along the same lines, I bought a sheet of this. The idea being that, as long as I can cut the inside diameter close to what I need, I can even double or triple layer them to get an appropriate spacing from the case. I also have some cyanoacrylate that has been rubberized or carbonized or some such thing.

I will post a pic if it works and looks like it was made by, at least, a 6th grader

A sheet of sorbothane cut will do it. More solid than the foam you have, yet more sticky and pliable so it will make a seal. It's like rubber that is just barely a solid enough that it can't be pulled apart or kneaded. Like a stickier, gummier, more pliable version of wiggly worm plastic fish bait. More expensive though. You actually have to peel it off when you remove it.

 

[Cicero]

Personally, I wouldn't box it up myself at all. The case of the sensor looks good enough to sit in the open and looks like its designed to be "exposed" anyway and sit in normal air conditions.

So what I would do is buy a case for your external electronics (veroboard your design instead of breadboard), then mount the sensor onto that case. The only thing exposed would be the cable going to the sensor, which I think is fine.

 

[JimB]

Personally, I wouldn't box it up myself at all. The case of the sensor looks good enough to sit in the open and looks like its designed to be "exposed" anyway and sit in normal air conditions.

That was one of my thoughts, but the electrical connector is not exactly a robust type suitable for exposure to the big bad world.

Maybe a good solution would be to mount the sensor on top of the electronics box, and to fit a simple "bracket" to provide mechanical protection to the connector and wiring.

JimB

 

[Cicero]

That was one of my thoughts, but the electrical connector is not exactly a robust type suitable for exposure to the big bad world.

Maybe a good solution would be to mount the sensor on top of the electronics box, and to fit a simple "bracket" to provide mechanical protection to the connector and wiring.

JimB

Perhaps, but its not like this can be in water, or needs a high IP rating. I dunno, I'm weary for over engineering here.

Those Molex connectors sit very snugly and latch, the wires are crimped, and so I would think for an internal shop type environment will likely be ok. https://uk.farnell.com/molex/15134-0801/cable-assy-8pos-rcpt-rcpt-100mm/dp/2671475

 

[DrG]

Thanks for the replies. In an odd sort of a way it is gratifying that at least others see that the sensor has some difficulties with packaging.

The bottom of the sensor has three screw holes so having it standing outside or on top of a project case could be accomplished relatively easily. The connector is a PITA. I tried buying just the inserts and making the wires myself and that was a flop (I do not have such a tool and they do sell a specialized crimp tool). I ended up buying pre-crimped leads . Still, these are not rock-solid connections like soldered wires. If I recall correctly, a cable with all leads attached (only four leads are needed for the project) is also available {as I am typing, I see that Cicero just provided a link to that cable) and that might work. It is not the socket/plug per se, which is a nice tight fit, but the leads that I am concerned with leaving open to handling/pulling problems (edit: maybe some strain relief if the sensor is mounted on top of the case).

The supporting circuitry is pretty simple and consists of only a Teensy-LC board (a cheaper Arduino board would work fine), and a display (I currently am using a tiny OLED (128X32) and I should probably replace that with a larger I2C LCD). Not a big problem. Power is via a USB connector and that makes it easy to use line or battery.

Yesterday, I spent some time sizing up whatever project cases I have on hand and none are particularly suitable. I do have one of these hanging around and It would fit an UNO and a standard 2 X 16 LCD and the sensor. I also had my eye on this one. I know that there are a bazillion project cases out there and I will need to do some searching.

I also came across these as a potential duct - I would need to drill them out of course but they come in various sizes.