FacebookTwitterDiggStumbleuponGoogle BookmarksRedditTechnoratiLinkedin

Bob Higgins open sources his programmable back pressure regulator design

Written by Robert Greenyer on .

Bob Higgins has been building a programmable back pressure regulator in order to try to precisely keep a maximum pressure (above gauge) in a reactor core so that, for instance, pressure profiles claimed to have worked can be closely emulated - like those of Parkhomov.

The USB driven prototype controlled back pressure regulator circuit is now working but, as of this blog post, it is still missing a 10 micron orifice to slow the out-flow of the small volume of gas that would be in the reactor tube when the solenoid valve is activated.

Bob Higgins' USB backpressure regulator prototype


Figure 1: Bob Higgins' USB backpressure regulator prototype


The valve is supposed to be 12V 6W.  What Bob found though was that the coil is 18.9 ohms and it will activate at 3.5V and then will not close until the voltage falls to 1.0V.  At 5V, this coil will draw 265mA, so the possibility exists for it to be a fully bus powered device.  Bob will program the USB chip to tell the computer that the USB system could take up to 300mA.  Bus powered devices can be supported up to 500mA.  Once the valve is opened, it only takes about 60mA to keep it open.

The pressure is set to max. for the sensor's operation (in this case 250 PSI) when it is powered.  The device appears as a virtual serial port.  You send it bytes to program what pressure it will regulate at.  Each bit in the programmed byte you send changes the regulation by the (sensor range)/255.  The device echo's the byte you have programmed it to.  This should be easy to control from almost any control program, including Labview.


Figure2: Bob Higgins' USB backpressure regulator schematic

It is possible for this design to be modified to be bus powered, but the 5V LDO regulator would have to be replaced with a boost or buck-boost switching regulator.  For now, Bob will simply make this a <100mA USB device with an external 7-10V isolated supply to power the solenoid (mostly).  The drivers come from the USB chip manufacturer (FTDIchip.com).  FTDI has good driver support for: Windows from Win98 - Win10 (16b/32b/64b), Linux, Mac, and even Android.  The device will appear as a Virtual Com Port.  To change the back pressure regulation value, you send 0x00-0xFF to the port with 0x00 being max sensor pressure and 0xFF being 0 pressure.  The device will respond with 0xFF and then the value you programmed.  The pressure will fall until the programmed value is reached.  Use of a 10 micron flow orifice is recommended for the small volume of H2 in the Parkhomov-like experiments.  This is calculated to cause the gas pressure to fall at a sensible rate for the solenoid to control to the programmed pressure.  The flow orifice has not been tested, as of this blog post, to compare its flow resistance to what is calculated.

Most of the parts are easy to find - most are from Digikey, including the pressure sensor.  The hardest part to find was the M12 cable for the pressure sensor, which Bob found at Allied Electronics.  Bob bought the Gems solenoid valve from Amazon (believe it or not!).

Bob's prototype is constructed on a solder-less breadboard.  I made small adapters for the SOT-23 parts using small pieces of square pad vector board (the software engineer he used to work with called these "spiders").  The prototype is fully operational in evaluation testing so far.  Drivers used were the FTDI VCP default x64 bit driver for my computer (Win7).  I used RealTerm to communicate with the board over the virtual com port for testing.

Bob will hand wire a permanent version for his experiments.

If others are interested in building this programmable back pressure regulator, Bob - or perhaps another community member - may consider laying out a small printed circuit board. Please let us know in the comments below.

Add comment


Security code
Refresh

Comments   

 
0 #19 Ignacio 2024-01-03 09:37
I cherish the nuanced view you gave on this subject.
It is actually unusual to find such balanced material.


My website Ron Spinabella: instapaper.com/.../1652102470
Quote
 
 
0 #18 Keith 2022-10-07 16:04
A fascinating discussion is worth comment. I believe that you need to write more
on this topic, it might not be a taboo matter but usually folks don't speak about such subjects.
To the next! Kind regards!!

my web page binomo indonesia: varindia.com/.../...
Quote
 
 
0 #17 먹튀사이트 2021-10-27 19:50
Heya i am for the first time here. I found this board and I find It really useful & it helped me out a lot.
I hope to give something back and aid others like you helped me.
Quote
 
 
0 #16 main-menu 2021-10-17 14:52
I see it as the simplest sort of online enterprise to begin and earn a lving from.
Quote
 
 
0 #15 trading apps 2021-10-16 21:22
Dies ist ein perfektes Beispiel für einen rationalen Handel.
Etliche Trader sind allerdings nicht in jener Lage, große Verluste zu verarbeiten, da die Emotionen eines solchen Verlustes zu irrationalem Verhalten administrieren.
Quote
 
 
0 #14 Titus 2021-10-10 15:10
The best part a couple of direct eCommerce website iss the extent of control you could have over your store.
Quote
 
 
0 #13 Boris 2021-10-10 01:41
You’d monetize by charging an ntry charge, selling advrt house, selling consumer knowledge, that sort of factor.
Quote
 
 
0 #12 discuss 2021-10-09 22:11
This is why you want a solid launch plan to make certain that all off the
tasks are accomplished on their predetermined schedule.
Quote
 
 
0 #11 Dewayne 2021-09-20 08:47
After I initially commented I appear to have clicked the -Notify me when new comments are added- checkbox and now whenever a comment is added I get 4 emails with the exact
same comment. Perhaps there is an easy method you are able
to remove me from that service? Kudos!
Quote
 
 
0 #10 คาสิโนออนไลน์ 2021-09-06 23:19
Hey! This is my first comment here so I just wanted to give a quick shout out and tell you I truly enjoy reading through your
posts. Can you suggest any other blogs/websites/ forums
that deal with the same topics? Thank you so much!
Quote
 
 
0 #9 คาสิโน 2021-09-01 01:08
It is the best time to make some plans for the future and it's time to
be happy. I have read this post and if I could I want to suggest you few interesting things
or tips. Perhaps you could write next articles referring
to this article. I want to read more things about it!
Quote
 
 
0 #8 คาสิโน 2021-08-25 23:40
Hi there colleagues, how is the whole thing, and what you want to say
concerning this article, in my view its actually remarkable for me.
Quote
 
 
0 #7 web page 2021-08-15 02:50
An outstandinbg share! I have just forwarded this onto a co-worker who has been doing a little
homework on this. And he in fact bought me breakfast simply because I
stumbled upon it for him... lol. So let me reword this....
Thank YOU forr the meal!! But yeah, thanx for spending
time to talk about thiks issue here on your blog.
การพนันฟรีโดยไม่ต้องลงทะเบียนเพื่อเล่น web
page: coolplace.com.au/.../... สล็อตคาสิโน เครื่อง
Quote
 
 
0 #6 site 2021-08-09 02:32
What a stuff of un-ambiguity and preserveness of precious knowledge on the tpic of unpredicted emotions.

Kasino rus site: quickproforum.com/.../... dan Judi
Quote
 
 
0 #5 shopescort 2020-01-15 07:07
Good day! I know this is kind of off topic but I
was wondering which blog platform are you using for this site?
I'm getting sick and tired of Wordpress because I've had
issues with hackers and I'm looking at alternatives
for another platform. I would be fantastic if you could point me in the direction of a good platform.
Quote
 
 
0 #4 info notebook 2018-01-30 02:40
Hi! I'm at work surfing around your blog from my new iphone!
Just wanted to say I love reading through your blog and look forward
to all your posts! Keep up the outstanding work!
Quote
 
 
0 #3 Robert Ellefson 2016-01-31 20:48
Great work Bob! This looks like a really useful device, and is remarkably simple to boot. I admire simple solutions like this, because I gravitate towards the complex end of the design spectrum way too quickly, and only arrive at simpler solutions after going full-circle first and ultimately discarding much of what I initially design.

I do have a bit of concern about the pulse generation function of U7 in your circuit, however. I realize that the prototype is working, but you are exceeding the specified maximum rise time of that gate (10ns/V is max per datasheet). Perhaps it would be best to change U7 to a schmitt-trigger ed buffer like the NC7SP17, which has input hysteresis and no maximum rise-time. This is the type of issue that can work fine in a prototype, but then exhibit unexpected behavior with a new layout, environmental conditions, process variations, etc.

Also, the simultaneous pulse at the FTDI chip's WR and !RD signals appears to violate the data sheet timing specs, which states a delay from !RD assertion to data valid of 20-50ns, and a data setup time prior to WR assertion (high-to-low edge) of 20ns. Again, although this is working in the prototype, it might not work under other conditions, die revisions, etc. Perhaps the use of a dual monostable multivibrator (I love that name) like a 74hc123 (or variant) would be good choice, to create a more robust timing circuit for the FIFO read, FIFO write, and ADC write signalling events.

For the 12V circuit, given the risk of hazardous ground interactions from an external supply, I would recommend adding a simple 5V->12V boost circuit like the LT1935 or similar high-switching- frequency, integrated-swit ch DC/DC controllers. This part costs $2, and uses minimal external components, including very small magnetics, and comes in a SOT23 package. It's a simple and sweet solution for what looks to be about $5 in components. There are also many monolithic micro-modules that can achieve this with less effort, for a little more cost.

Also, it might save some folks future headaches if you included series resistors on the +5V and pressure sensor signal lines that are leading to the off-board DAQ system, in case of wiring or configuration mistakes. 50 ohms should be sufficient for current-limitin g, and would also help reduce any ringing that might arise during rapid signal swings reflecting off the cabling impedance mismatch.

I hope you accept this design review feedback in the constructive manner it was intended, rather than as criticism. I think you're doing a great job here, and hope you keep it up. You're setting a wonderful example of open science and engineering for public interest.
Quote
 
 
0 #2 jeff morriss 2016-01-30 03:11
Quoting Alan Smith:
Nice work guys. If you want to try to make a 10 micron hole yourself, without resorting to lasermicrodrilling - which is commercially available but not cheap - I can only suggest you try using 6mm. soda-lime glass capillary tubing. Heat the centre of a piece to softening point and pull/stretch the ends apart.

Depending on how hot you get it and how fast to stretch it you can certainly make some microscopic tubes. Many years ago we used this technique in the lab for making hypodermic needles to puncture the nuclei of mouse white blood cells so we could suck out the contents and transfer them to another cell. All done by hand under a microscope, too!.


If you want a 10 um orifice consider using Swagelok VCR fittings. They make snubber washers with very small laser drilled orifices. I'm not sure if they go all the way down to 10 um, but a web search should give you an answer.
Quote
 
 
0 #1 Alan Smith 2016-01-29 10:40
Nice work guys. If you want to try to make a 10 micron hole yourself, without resorting to lasermicrodrill ing - which is commercially available but not cheap - I can only suggest you try using 6mm. soda-lime glass capillary tubing. Heat the centre of a piece to softening point and pull/stretch the ends apart.

Depending on how hot you get it and how fast to stretch it you can certainly make some microscopic tubes. Many years ago we used this technique in the lab for making hypodermic needles to puncture the nuclei of mouse white blood cells so we could suck out the contents and transfer them to another cell. All done by hand under a microscope, too!.
Quote
 

Here is your generous contributions so far towards our $500,000 target, thanks everyone! : $45,020   Please Donate
See the current state of our booked costs here