Build an IoT DMM, hardware engineer with smattering of software seeks software engineer ... / Computer Science / Forums

Forums

4hv.org :: Forums :: Computer Science

Next topic »

Build an IoT DMM, hardware engineer with smattering of software seeks software engineer ...

1 2 next

Move Thread

LAN_403

Dr. Slack

Fri Jul 06 2018, 02:30PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

... with some vague interest in hardware.

I play around with software, reasonably competent with python and microcontroller C, but have never really reached critical mass on things like linux, git, sockets, I2C. While I can search around for how to do any one thing, it's all a bit of a struggle. I'm aware that trying to invent too many things at once is likely to founder. So I regard my idea for a wifi enabled meter a bit too big for me to do on my own.

The general idea is this. Control and wifi done by something like Onion Omega 2+ (other micros are available). I've got options for the front end more or less sketched out in my mind. Two channels of voltage from 100mV to 1000V, three current channels (electronic switched pA to 1A or 10A, socket selected 1A to 10s or 100s of A, and a low accuracy log reading nA to A for wide instantaneous dynamic range, 2T/4T resistance, temperature, and maybe a few relay outputs for controlling battery test loads. What I need is a web interface that can be operated from a browser, and an API that a program can talk to.

This is just for fun. I'm not anticipating trying to sell it. That would involve timescales, specifications, funding, responding to competition. I'm retired, I don't need all that.

Anybody want to play?

Sulaiman

Fri Jul 06 2018, 07:02PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Assuming that you are more into the software than the hardware;

You are aware of cheap usb or RS232 interface digital multimeters via eBay ?

I lost my Â£9.99 Maplin dmm w/RS232 but it was really useful for stuff like battery charge/discharge etc.

USB oscilloscopes with software are also available for faster stuff,

USB VNA and SDR cover the upper frequencies.

That would leave you just with the WiFi:USB to make/buy.

Dr. Slack

Sat Jul 07 2018, 04:59AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Sulaiman wrote ...

Assuming that you are more into the software than the hardware;

Perhaps I'm mistaken, but I thought I'd spelled out that my software was smattering, and I was more au fait with the hardware end?

wrote ...

You are aware of cheap usb or RS232 interface digital multimeters via eBay ?

Yeah, got one of those. I also use an Arduino as a crude USB connected multichannel voltmeter for battery charge/discharge monitoring, it's how I got the 'AA shoot-out' results

of a while ago. My 4 channel Rigol will go fairly slow for monitoring tasks as well.

Am I correct that you're saying that you're not the man for the job?

Shrad

Mon Jul 09 2018, 06:48AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

I'd use a ESP8266 or ESP32 as it covers the complete range of your requirements, plus it can host the web interface without any hassle... and it is covered by arduino IDE and libraries for what I know

Sulaiman

Mon Jul 09 2018, 08:34AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Dr. Slack wrote ...

Am I correct that you're saying that you're not the man for the job ?

Based on my ability to appreciate the question,
I gues the answer has to be ... YES
You have the wrong guy :(

Plasma

Sun Jul 15 2018, 11:28PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

I might be able to help, couple of questions
do you want a Web server thing to accept Get and Post requests or just socket sending hex across the wire, do you need dns and tcp/ip stack made or is Linux taken care of that.
Got a couple of projects on but one computer so don't want to set up Linux, using Windows, so any code want be tested.
Can you post the code you're done, would be easier going from there

Dr. Slack

Mon Jul 16 2018, 06:18AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Get and Post. I've often seen those referred to as I google around. I don't know the difference, and what using either would do for me. What should I want?

As far as I can tell, you ask for UDP or TCP at socket setup time. Though my minimalist nature leans me towards UDP, TCP would probably be better, and closer in spirit to what serial I/O does. I do want something that doesn't hang, or is easy to detect and reset hanging behaviour, should ends get unsynced due to a disturbance on the LAN, program bug, or whatever.

The device should sit on my local wifi network, so having an address of 192.168.1.x, accessible to everybody on my LAN, just like my printer or ADSL, and not visible to the world the WAN side of my ADSL. That suggests I don't need dns.

I want two modes of behaviour. Whether that needs two interfaces writing for the device I don't know, it may be easy enough to handle both behaviours through just one. It's all low speed, so there's a lot of scope for doing things inefficiently.

Mode 1

When I set up my ADSL, it has a web page I visit, that I can fill in and read values. I'd like to be able to do something like that, using a browser as a very manual method of driving, for initial setup, debugging etc, zero programming at the client end. I tell it to change the range of a channel, read a voltage, no more. The web page would essentially be a soft front panel into the device hardware. Once the web magic gets as far as running a program, preferably python but C would do, that presents one button and one entry box on a web page, I know where I am and can do the rest.

Mode 2

When I plug an Arduino into my USB, I can program it to work over serial I/O, and write a python program on my PC to talk to it, that works fine. I understand essentially the same thing can be done over sockets to a device on the LAN. That's the mode I'd want to use for running it automatically from a custom python program. I'd write my battery charger/tester or whatever else in python, and use the device as a fairly dumb peripheral, just as I've written a battery tester to use hardware hanging off my Arduino board.

If it's possible to fake this mode from the first, and I suspect it is, by using the host PC python program to construct web requests, then maybe I only need mode 1 on the device. However, I suspect mode 2 is an order of magnitude easier to implement, at least on the device.

I've looked at python socket tutorials and been left confused. I've read around peoples' experiences putting such things together, and found things like 'it will work on loopback but won't work over my LAN', which have inhibited me from mustering enough effort to put something together and try. I have not yet reached sufficient a critical mass of knowledge and warm fuzzy feeling to start along the path of trying things out. I do not yet know what a good tutorial looks like, a pointer at a good one might be sufficient. I always have this difficulty starting with new things, don't understand until I've got my hands dirty, can't bring myself to get my hands dirty until I've got some basic level of understanding of what I should canonically be doing.

The path would probably be something like this.
1) Write a simple server that can be set, read, and generate new information, like a clock, running on the same machine as a client to talk to it over loopback, both ends in python. Implement both modes.
2) Move the server to a different machine on the LAN, initially a laptop and then an RPi over RJ45 for instance.
3) Get an Onion Omega or similar, and repeat over wifi.

Software side 'hello world' achieved, I should be able to take it from there.

I only have linux Mint on my machines, but I can ask my son, who has python on his win10 laptop, to try odd things out from time to time if necessary. I do use wine for things like LTSpice, but don't want to introduce yet another potentially buggy interface into a process that I'm already struggling with. I had rather hoped that working over LAN would be fairly platform independent, with python to take care of any differences.

Shrad

Mon Jul 16 2018, 10:34AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

try this kind of implementation :

easy, fast, repeatable

Plasma

Mon Jul 16 2018, 11:25AM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

If a client sends a Get request, the values get added to the Url, if it is post it is values in the page.
I would probably get a client to send a request to the server, something like 192.168.2.2,you server on Linux sends a packet /string array back to the client using write socket with \ r\n \r \n as the last four bytes, you can then use a Web browser on the client, the string array is just copy paste of a Web page.
The Web pages has box's to enter data, HTML and JavaScript with a sibmit button that sends a Get request to 192.168.2.2/index.html/volts=200mV,display=1sec the sever code receives data of GET index. Html/volts, you use string functions to parse the read socket looking for volts= you then send that value to the hardware.

On Mint download or install "wireshark" it's a network packet anylser it will show you what a request from a Web browser looks like.

Sorry hope it helps

Dr. Slack

Fri Jul 20 2018, 10:12AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

@PLasma Let's see if I can start hauling myself out of the swamp.

I've located the python http library, which will serve files like the default index.html when you access the base site. I'm trying to understand when the choice between making a get or post request is made? Is it the case that the html in that page has javascript in it which constructs either a get or post request when the client at his browser hits a button or makes some other triggering action? The server library has functions like do_get() and do_post() which I would imagine get called at the obvious times?

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob