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  #1  
Old 11th January 2017, 01:39 PM
TablePC Offline
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External device software

Mostly I write software where a PC is connected to some external equipment to gather measurements or make a mechanism do something. Currently I am writing Python code that controls circuits to run a small mechanism.

I am just curious if there are other people here that do similar projects. The other forums I am aware of where people are doing this sort of software are windows oriented.
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  #2  
Old 12th January 2017, 02:46 AM
ocratato Offline
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Re: External device software

Given that I came into computing from the hardware side of things, and I have a reasonable collection of electronic bits, I am quite surprised that I have not embarked on a similar project.
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Old 12th January 2017, 04:06 AM
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Re: External device software

I started my computing career in the '70s building emissions testing systems for a diesel engine manufacturing division of GM. The computers then were expensive and limited by today's standards.
The code was memory resident and written in assembly.

I am retired now, but have been working with a Beaglebone Black and just got a Raspberry Pi 3 for Xmas.

The Raspberry coding will be done in Python 2 or 3 ( not sure yet which is best suited ) The power available on these chips is amazing compared to the constraints we used to have to work with. My current interest is to duplicate the data acquisition and control approach we used in the '70s with Python on a RbPi3. I'm betting it will significantly outperform that era's solution ( if I can figure out how to twist a Python solution into the proper shape)
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  #4  
Old 12th January 2017, 02:49 PM
TablePC Offline
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Re: External device software

Yeah! I'm glad to see there are Fedora folks that are hardware folks too. Thanks for your replies.

I also started in the 70s While I was in school there was an IBM 360 system that students were allowed direct access to and the local IBM Customer Engineer taught me to write Basic Assembler Language with Channel Commands and everything. That came in handy when I went to work. After I designed the control electronics for a tape drive, which included and MC6800, I got to write the hex code to run it. It was a challenge, but good fun too. Getting all the functionality to fit in just 8K bytes of memory took a while.

I am retired now and rather than taking the embedded approach to things I decided to use a PC to be the "brains" of my projects. Since GPIO and analog boards for PCI-Ex are very expensive and the APIs available for them are written for Windows, I decided that my projects from now on will interface via USB.

Finding a USB GPIO / Analog I/F device took quite a while. There are lots of chips and a few little circuit boards, but again all the supporting APIs are for Windows. Though a couple of them made the source code avaiable. I bought one of the boards and went to the trouble of doing a reverse on it. I got it mostly working using pyUSB, but it was also more money than I wanted to spend and it came as a kit. I don't mind assembling my circuits, but I saw assembling that USB I/F as an addition to it's cost.

Finally I found a company called Numato Lab they have a selection of boards that are USB with GPIO and read only analog. The boards pretend to be a TTY device so they can be accessed via the Python Serial API. Numato provides the commands and arguments in the their manual. They have 8, 16, 32 and 64 bit I/O boards. I'm on my way with USB interfaced projects. I'm not sure how fast I can make it go, but speed isn't a huge concern for my home projects. Now my projects don't need to have control panels. Though I must say I am a bid saddened by the decline of knobs, buttons, meters, dials, etc. etc. instruments and computers used to be very impressive sights. It was very impressive to watch the front panel of the System 360 while it was running. Now everything is a nondescript box.

Ocratato, jump in the water's fine!

Last edited by TablePC; 12th January 2017 at 03:16 PM.
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  #5  
Old 12th January 2017, 04:47 PM
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Re: External device software

Now retired, I look at personal projects such as my home heating system. My project -- use an outdoor temp sensor, an indoor temp sensor, analogue thermostat, timeofday clock, and a-to-d converter to control a home heating system.

My home heating system is a circulating hot water (radiator) system, with a boiler and integrated temperature sensor. The idea is to provide comfort based on time-of-day, and to do it as economically as possible. Time constants are in minutes, rather than microseconds. The circulating water temp is based on the outdoor temp, and the difference between the thermostat setpoint and the actual room temperature.

I need to implement T=ax + by + cz + dT where x,y,z T are indoor/outdoor/boiler/clock inputs and T is in the feedback loop. We seniors have brains, don't want our brains to get rusty. We also have budgets to respect.
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  #6  
Old 12th January 2017, 05:09 PM
Kobuck Offline
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Re: External device software

I have also looked at the Numato products and I like them also.
However, I find they suffer from the same limitations as the RPi3 I/O. I completely understand why current logic outputs are implemented at 3.3V, but this leaves you with a significant effort/investment remaining to get to useful working voltages.

When we had 12V available you could at least fire a relay coil (this really dates me ) to switch AC voltages.

I have also found OPTO22 has some offerings. They have been in the business for many years and still offer a complete path to useful working voltages ( by this I mean switching AC ant 1 or 2 amps, and/or 12/24/48 VDC ). There is even a module for mounting a Raspberry Pi to an I/O board.

Don't get me wrong, I will be using 3.3V logic during proof of concept. However, a useful solution requires the ability to control physical devices.
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  #7  
Old 12th January 2017, 09:22 PM
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Re: External device software

Solid-state relay might be an option for this case, it can fire as low as 3V.
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Old 12th January 2017, 10:05 PM
Kobuck Offline
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Re: External device software

Quote:
Solid-state relay might be an option for this case, it can fire as low as 3V.
A solid state is a good solution, but costly compared to old fashioned relays.

I was not very clear in my post. I was trying to reference how the cost of a solution still needs to get to useful working voltages.

A low cost logic card like the RPi3 with 3.3V logic still needs to be coupled with devices to produce higher level outputs. The Solid state relay costs $10-15US per point for a reliable device and may require additional cost of cooling fins for continuous duty cycle. ( relays are $2-5US) The Numato products are a slick low cost solution for PC I/O , but still leave you at 3.3V logic levels.

The OPTO22 solution appears costly until you add up the costs of getting to AC levels of output with discrete Solid state relay devices.

This is more an outline of how I am analyzing my desired approach. I have not yet decided what the "best" approach is. One of the biggest issues is getting reasonable pricing for low volume "hobbyist" buys. I don't want to build 10,000 dishwashers, I just want 32 I/O points.
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  #9  
Old 12th January 2017, 11:57 PM
TablePC Offline
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linuxfedorafirefox
Re: External device software

The heating system control seems like a great project.

My current project is a simple motor drive and monitor a couple of sensors that will be a demonstration for a protege of mine. Then I plan to implement the final interface design as my standard control front-end for my projects.

I think the 3V I/O will be with us a while. Not only the 3V, but the low drive currents that go with them in output mode. The good news is that these newer devices use very little power compared to the old days and there are ways to deal with the voltage levels and the need to drive more current.

Another issue I dealt with was the desire to isolate may project electronics from my PC. I don't what my PC damaged if something goes wrong in a project circuit.

I solved both issues by putting opto-isolators between the Numato board and my circuitry. The only connection between my project circuits and my PC is light. So it provides excellent isolation for my PC and allows me to shift voltage levels if I need to. Quad optos are pretty cheep these days. Of course opto's can't drive high currents either, but I can get to the voltage levels I want then deal with the current as needed. The only other thing I had to be careful of is that the Numato boards can't drive much current (25mA total or 3mA average per I/O pin for the 8 bit board). So I made sure the Opto's I picked had a high enough "gain" so I didn't need much current to drive the opto's.

As for high DC currents and AC: I also like and use Opto 22 devices. Particularly whenever I need to switch line voltage or another AC circuit. When I need to switch a higher current DC circuit I just use a power FET. They're cheep and there are several available that switch on with a gate voltage of 3 volts or less.

I'm hesitant to get into any detail here as I don't want to upset the other folks that use this forum for purely software discussions. Dose anyone know of a forum for hardware project people that is linux oriented or better yet Fedora oriented?
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  #10  
Old 13th January 2017, 12:27 AM
ocratato Offline
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Re: External device software

There seems to be some interest among the forum for this sort of discussion.
Perhaps you might ask the admins to add a subforum under "Exploring Open Source" for discussions relating to external hardware.
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  #11  
Old 13th January 2017, 03:16 AM
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Re: External device software

I don't know all the forums available by any means, but I often visit linuxquestions.org. They are not fedora-centric so anything related to any flavor of linux or almost any project you can think of is fair game there, and a lot of users are on the board a lot of the time.

There also are lots of results for users of the raspberry pi if you do a quick search for that term. Some quick searches and remembering that linux does not mean fedora only can broaden the field of experts (or just fellow users) that can answer a lot of questions and make suggestions for you.

I too came from the 70s and worked my way up over time and hardware changes to present day.
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  #12  
Old 3rd March 2017, 02:18 PM
TablePC Offline
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linuxfedorafirefox
Re: External device software

I asked one of the admins about this and they said we could continue making posts concerning co-development of hardware and software here in Programming & Packaging. I think I'll start a new thread on tools.
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