DIY DIY EC Meter

[donkeykong]

Cheers guys!

Nice profile pic RedEyeC , im an old cypress fan also.
Went through a cypress hill phase just a couple weeks ago, pulled out IV with AudioX etc on it and banging it loud in the car. Takes me back to them golden days with my cheap sub mounted on the back of the parcel shelf of the mkII golf that would never warm up in the winter
The Harmon kardons did a fair job on it, for that moment I was 15 years younger

 

[donkeykong]

Good stuff, wish there was a DIY ph meter! Great job bro

Cheers! Actually the plan will involve a DIY pH meter and more later. Its next after the EC circuits are locked down in design. I got me some pH calib. fluids already in prep as I was ordering in the EC fluids anyway.
Didn't delve so deep yet but I think it *should* be straightforward, but for that Im not planning to build probes. There seem to be loads avail at reasonable cost compared to the EC probes, and I think their useful life is limited, so the thing to do will be to interface to them well.

Im not sure if I'll stick with the DIY EC probe also, but I want to see how it performs and maybe it surprises us. A V2 of this DIY probe would have a thermistor also, close to the conductors, then it has a chance. Temp compensation is important, and generally EC meters convert to EC@ 25deg C and show that reading on the LCD. Previously I thought a separate temp probe in the same tub would be good enough, but lately I considered it best to read that temp from as close to the probe head as possible, avoid errors de to local temp gradients.
With this one I will try to gauge the performance, use an external temp probe and see if it can possibly keep up with a commercial offering, like the RS probe I have to compare with.

Managed to wangle borrowing an expensive BlueLabs meter just to get an exact and second reading on the arbitrary EC solutions I've made up (5l+ in tot with 5 different strengths in anticipation for lots of testing later!).

Stay tuned, pH is in the queue. As is carbon dioxide level and dissolved oxygen
I'll prbly create a new thread for that in the DIY section to save having one ridiculously long thread where its hard to separate these topics and find the right info.

 

[donkeykong]

sorry folks, been out of action a few days with food poisoning ! feeling a lot better now thank god, that was no fun at all :no:

not so much to update at the moment. did manage to get that new LCD screen up and running, and the "clone" arduino by sainsmart arrived also (works perfectly fine like the original, groffwiwi).
also I have a bluelab combo meter on my desk now so there is some decent kit to compare results with soon.

thinking about starting to house this stuff in a box next , save ending up in a rats nest when things get more complicated.

 

[donkeykong]

few bits of progress to report on, firstly I rebuilt my PC as its random crashes were driving me up the wall. Its done alright since its nearly 6 years old, far longer than I've gone before without a complete mobo and cpu swap. It used to be a quad core Athlon of the older generation which drew a lot of power and generated a lot of heat, so was overclocked and watercooled.
Fitted its first SSD couple years back and the performance jump was so big, I didn't need to upgrade anything else for blistering performance. its like the real bottleneck had been removed.

The new beast is up and running now, its an i7 4770K clocking in at 3.7Ghz , 16GB of 1600Mhz DDR3 , 240GB SSD (540MB/s both read and write).
Damn its quick, windows loads in about 8 seconds

The other task I been on is getting the LCD screen connected into my controller, not so simple as I want it on cables so it can be mounted on the front of the box. The standard "TFT adaptor shield" is no good for this, though I have one also, which turned out to be very useful to compare to since Sainsmart's schematics they give and docs are not great.
Took a couple of nights to connect it up, debug it to working and test all functions (screen, touch controller, SD card interface )

I've basically rebuilt the electronics and connections that the "TFT adaptor shield" make, and done it much smaller and in-line. The ribbon cables from the arduino run to a small adaptor PCB which has the connector for the LCD. On that PCB there are about 38 resistors mounted, which is what is required for the task at hand, adjusting from the arduino's 5V interfaces to the LCD's 3.3V .
I used dot matrix stripboard which does not connect in lines like veroboard you might know. Each hole has a square pad around it and connects no where, you make the connections. In this case all the lines that needed resistors, I mounted TINY 0603 case size SMD resistors in-between the dot-matrix boards pads. A fiddly but very compact way to do it. Like I said two days in total, could have been a little quicker if Sainsmart's documentation was accurate. That's what you get with Chinese stuff I guesse.

Good news is that it works, now the LCD is connected to my board and I've tested the screen output as well as the touch controller interface, all good. As a final nicety I implemented their SD card interface and confirmed I can access the 2GB SD card I have in there to test. This Im sure will be useful later when I want to log data, load a background image for a screen etc. Nice

The crap on the screen at the moment is just drawn on with my finger, touch controller is working OK.

 

[A4]

Sick man, just sick! You are upping the game for us controls electricians on the forum! I was considering building a plc based control panel with touchscreen and wireless capabilities so I could see what was going on while I was at work. Looks like I am going to have to get my butt in gear.

I am subbed for the remainder. Great work DK and some +rep for the show.

 

[donkeykong]

cheers mate! do let me know if you have any ideas to throw into the pot along the way. Id love to do something that others can use in an easy way later.... so far only the brave would try to recreate this dev kit as it is. But later I want to get all the schematics I arrive to all together and have a few professional PCB's made up which will make it simple like plugging on the arduino, lcd and probes. Want to keep it low cost, at least for what it is/will be.

 

[Groff]

hey DK... I haven't bought the sainsmart unit 'cos I found a vendor that does really sweet ebay auctions. I can get a complete starter kit for as little as 20€-30€ direct to my door, but I've yet to win an auction :Stones slap:

Anyways... Should I get one, or do you think the lack of documentation and differences to arduino will be bad for complete noob?

 

[donkeykong]

hi mate. to be honest I think most clones of that kit will work fine. its because the arduino design is open source, everyone has access to the design and it just depends who builds it, it comes out the same in the end, and the official guides and many libraries should work exactly the same as Mega2560.
there are a few versions of the Mega2560 btw. The original and the clone I have are both Mega2560 R3, check if yours is a clone of R3 or an earlier version. I cant remember exactly the difference but some HW pins I think and maybe more memory, you can prbly look it up.
that's sounds like a really good price if you can get it for that btw!

 

[CGR]

all caught up and sub'd.......and here you go

 

[donkeykong]

Managed to get a few more things done over the last few days. Not yet on to the exciting stuff, checking out the EC circuits, but instead I put things together in a better way that will pay off later!

First off I put a new socket on the power supply, uses a 6 pole DIN to carry all the voltages across to the equipment. +/-5V , +/-12V and Ground.



Next the circuit board , the LCD and its interfacing made it into an instrument box, Ive cut out for the Arduino's USB, the DIN jack for the power, and the front for the LCD. It has a touchscreen so this will save needing lots of buttons.
The power from the DIN drops down onto my PCB with a header connector. I also mounted 2 4-pole DIN connectors on the back, this is where the EC probes will connect on to, I'll add more jacks later.
I also sorted through the codes for Arduino to drive the LCD unit bits, so I have the screen, the touch sensor and the SD card libraries in the project and working OK.




Next Ill need to put a few more header connectors and stuff on the PCB, its going to act like a "motherboard" and host the different sensor circuits Im later going to be doing.