DIY: The Ultimate Vacuum Gauge/Switch - RC Groups
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Sep 15, 2017, 08:51 PM
myday.. myday
LA8PV's Avatar

DIY: The Ultimate Vacuum Gauge/Switch

This is a crash course on making an accurate vacuum gauge with a fully adjustable vacuum switch suitable for vacuum pumps not capable or suitable of running continuously.

Comments and questions are always welcome...

First I will present the parts I am going to use, I will try to avoid using direct web-links to parts and such because I don't want to be accused of advertising for anyone but it should be easy for you to search it up if you are interested in this. However, if you still can't find it I will help you.

Main parts list:
- Arduino compatible Nano V3 (prototyping board)
- Arduino compatible Nano V3 I/O expansion shield
- Arduino compatible Relay module
- LCD 1602 display with (or without) I2C interface
- MPX5100DP differential pressure sensor

Additional parts:
- Toggle switch (1pc, pump on/off)
- 10k potentiometer (2pc, threshold/margin)
- Push button (1pc, switch modes)
- Colored 3-5V LED's (2pc, pump on/warning)

Additional stuff:
- Electric junction box or similar
- Wall outlet extension cord (cut in two to make I/O cords)
- USB charger/power supply (5V / 1000mA)

- If you already have another Arduino board or if you want to use a different one you can, no problem.
- The most common Relay module available looks like the one on the picture, it's rated capable up to 10Amp at virtually any Volts. However if you have a powerful high capacity pump or just want to be on the safe side - these Relays are also available at 30A.
- The LCD 1602 display is possible to use as it is but it needs a lot of connections, you can get these with an added "I2C interface board" that reduce the number of connections drastically. You can also get the I2C interface board separately. This display is also available as LCD 2004, this is a bigger version capable of displaying 4 lines of information at once instead of 2 lines. I like the blue ones best.
- About LED lights these usually needs a small 220ohm resistor to prevent them from burning out, you can get LED's as a small module as well if you don't want to mess with resistors.
- About connectors, the connectors on the Arduino board and modules is called "Pin Headers" and they are usually long strips that you simply cut to desired length, as wire/cords you can use servo wire - preferably as thin (soft) as you can get it. You can as always also get ready made wires with connectors attached if you want to avoid the soldering iron as much as possible, they might not be as good as the ones you make yourself though.
Last edited by LA8PV; Apr 10, 2018 at 12:37 PM.
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Sep 16, 2017, 05:20 AM
Have Wings, will Fly!
dont's Avatar
Watching with interest
Sep 16, 2017, 09:16 AM
Pylonracr's Avatar
Me too. I am too dumb to build one but I will watch him build his.

Sep 16, 2017, 12:13 PM
myday.. myday
LA8PV's Avatar
Even grandma can do this, if you have problems finding the specified parts let me know. You just need to connect them together the way I show you, eventually you plug in the power and it will work just like it should right away.

First step is to mount the parts in a suitable box.
I have just used a junction box from the local hardware store, not particularly pretty but functional. You can get all sorts of project boxes on the web, nice desktop designs, aluminum boxes, powder coated steel, etc...

I have used some scrap plywood to mount the parts on. The distance pieces is aluminum tube cut to length with a knife because that is what I had on hand, but some plastic tube or similar would be just as good. You can get ready made hexagonal brass distance pieces too if you want to make it real professional.

The only thing left in the bottom box now is a tube through the wall that goes to the pressure sensor, and preferably there should be clamps to secure the main wires/cords that comes from the wall outlet in to the relay and then goes out to the pump.
Sep 16, 2017, 03:46 PM
myday.. myday
LA8PV's Avatar
The top lid is finished, now I will go back to the bottom part of the box and finish the last few details with the tube inlet and main wires/cords and it should be ready.
Sep 16, 2017, 08:39 PM
myday.. myday
LA8PV's Avatar
Ok it's basically finished now.

You can see from the pictures that I have modified a small tube coupler and just fastened it with some glue, a piece of brass tube in a suitable dimension would probably work just as well.

My main cord clamp is perhaps not ideal because it is all metal and in one piece holding both cords, if it was to eat through the insulation due to vibration or extended use it would be a disaster. However I have softened the edges of the clamp with a file and put a couple layers of shrinking tube outside the cords to give them some extra protection, still I hope that you will come up with something a little better than this.

The only thing left now is to plug in all the connections but I want to do that when I write the program for it on my computer, so I will get back to that when I'm done with the basic program.
Sep 16, 2017, 08:43 PM
Hope to get out of life alive
kenh3497's Avatar
Originally Posted by Pylonracr
Me too. I am too dumb to build one but I will watch him build his.

I'm standing right beside you Scott!

Sep 17, 2017, 01:25 AM
Slow builder
_AL_'s Avatar
Great stuff & neat work.
I'll order some bits next week & start once they arrive.

Sep 17, 2017, 12:30 PM
myday.. myday
LA8PV's Avatar

About the Relay

I thought I'd do some explanation about relays.

I have used a standard 10A relay module in my example, this is a mechanical relay switch. A vacuum switch for a vacuum pump has a somewhat demanding task; it switches a power motor on/off and it does so at a high frequency (often).

The best solution for this is to use a "solid state relay" that have no moving parts, the reason I am showing you to use this standard mechanical relay module is because it is "plug and play" with Arduino. The high current solid state relays might need more than the 5Volt that the Arduino board provides to trigger it properly, so it's ever so slightly more complicated to make. Anyway this standard relay module that I have shown you is also available as 30Amp and this is made to be used for such as switching a power motor up to 1/2HP at up to 240VAC on/off, so it will likely be more appropriate for this use.

I will use the standard 10Amp relay when I test this device on my high power system and my guess is that it will hold up fine - but no one will know for how long...
Sep 18, 2017, 07:34 AM
Slow builder
_AL_'s Avatar
I've ordered the important bits tonight & they should arrive over the next week or 2.
I'm looking forward to this build.

Sep 18, 2017, 06:53 PM
Entropy is happening!
Jim.Thompson's Avatar

Have I missed something here?

The advantages of this digital high tech approach to the simple task of regulating vacuum pressure totally alludes me!
My 10 year old analog system made from scrap parts cost me the price of a .1 mf capacitor.
I already had a micro switch and a vac guage.
It has served my vacuuming needs with total reliability for countless vacuum jobs -- including changing the brake fluid in my car.

Can someone enlighten this old Luddite please?

Sep 18, 2017, 07:17 PM
myday.. myday
LA8PV's Avatar
I am about making the program for it and I need some help from you guys out there.

I am making it with switchable modes so that it can be used as: mBar, mmHg and inHg, right now I'm at the inHg mode and I have a question...

What adjustment ranges is important to you? Lets say you want to bag white foam, or perhaps you want to bag high-density foam, or perhaps you are working with molds. What range would you want to have at your disposal in "inHg" in those situations?
Sep 18, 2017, 10:53 PM
Pylonracr's Avatar
Since you asked. When I bag foam wings I like to use about 5"Hg, so a fairly narrow window would be beneficial. Pump on at 3.5 to 4" and off at 5" would be ideal in my opinion.

Sep 19, 2017, 06:16 AM
Slow builder
_AL_'s Avatar
I've been doing some research of late & it seems white EPS is ok up to around 8"Hg & XPS foam up to around 25"Hg.
I'm happy to be told otherwise but that seems to be the general info I've found so far.

The pressure sensor seems to be good to 29" so with that in mind, I'd say a range from 3" to 25" should do the job without over stressing the sensor.

I received my pressure sensor today from RS. Not bad considering I ordered it last night.
I already have some Nano & Pro Mini clones & more than enough switches & buttons.
Just waiting on the relay & LCD now & I can start assembly.

Sep 19, 2017, 09:59 AM
The Junk Man
Originally Posted by LA8PV
What adjustment ranges is important to you? Lets say you want to bag white foam, or perhaps you want to bag high-density foam, or perhaps you are working with molds. What range would you want to have at your disposal in "inHg" in those situations?
Ah yes, vacuum hysteresis during normal vacuum bagging, A topic close to my heart.

Most people always want to have a very narrow band for some reason... and that is unnecessary. It causes unnecessary motor wear and overheating. With ONE EXCEPTION (see below).

If you are bagging above 16"Hg then you do not need a narrow band. 4"Hg is way close enough.

The exception mentioned is if you are bagging low density foam. Anything over 6"Hg will crush it... and even 6"Hg is pushing things.

My regular vacuum pumps do not like operating this low. So I use either my GAST DOA-P704 diaphragm pump or my converted aquarium pump. Both of which are continuous run pumps. No need for a switch.

The aquarium pump pulls about 5 to 5.5"Hg reliably and I can set the GAST at any point necessary.

So beware of narrow band settings. They can burn out a pump very easily. Especially pumps that do not have relief mechanisms built in and are trying to start against full vacuum.

See the Joe Woodworker site for an explanation of bleed off to reduce the starting load on a vacuum pump. To long to go into here.


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