Another SITcore project

A project for a client to create a display for a water tank with Lora for the sending of the tank water level via a pressure sensor and upload to some online data site such as Thingspeak over WiFi.

The board works first time with the LCD module, a 4.3" 800x480 IPS TFT which is 850 cd brightness. The LCD is really bright and sharp at that resolution. The photo doesn’t do it justice. It is only 4.2mm thick. Interface is standard Newhaven and same timing as the 7" version so it just worked out of the box.

I am really starting to like SITcore now that I have a couple of projects built with it. There is another one in development with an SCM20260D with Ethernet and 7" LCD for a touch panel control system interface.

On this board, the SOM is the SCM20260E, WiFi via the WINC1500 and RFM69 for the Lora radio. There are also 2 spare RS232 ports for future expansion and a MicroSD card for configuration and storage.


Looking good!

How do you measure the water tank level?

What is that IC spot for towards the SD card?
Also, how did you go about impedance matching that Lora antenna? This concept has been puzzling me for a while now.

You can measure using pressure and convert to height using a simple formula. Fresh water density is 1000kg/m3. You need food grade sensor and cable but in general the stainless steel sensors are good for this so just need to pay attention to the cable type used. I use PTFE as this is food safe.

That missing IC is a MAX3232 that I thought I had in stock. I’ve ordered one and it will be here tomorrow. :slight_smile:

The impedance matching was done with Altium Designer PCB Software.


What kind of sensor would you use then? A strain gauge at the bottom of the tank?


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All pressure sensors are strain gauges so basically yes, and you use a submersible pressure sensor that measures low pressure. For a 3 meter tank, the max pressure at the bottom with 3 meters of water is only 19.06 psi of pressure so the changes are small for this type of application.

The sensors for depth also have a vent tube to the atmosphere that acts on the rear of the sensor to compensate for surface air pressure changes. Without this, a constant water depth would vary as the atmospheric pressure changes over the course of a day/week, etc.

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That’s cool and as Gus said, brilliant!

Thank you for taking the time to explain! I appreciate it.

In my deep well, I used pressure transducers that measure 0-100 feet of pressure(head), they are mounted with the well pump at that depth, they are 4-20ma devices that give a nice accurate 0-3 or 0-5 volt DC signal with the right resister in parallel, I use the regular resolution analog inputs in my micro. For my two static (non-pressurized) water tanks, I used ultrasonic level readers, mounted on top of the tank looking down, they are also 4-20ma. The pressure transducers were about $150 from China with 100 feet of cable attached (no splice in well), and the ultrasonic’s were about the same used on ebay. They have all been working fine for the last 8 years. Powered them with 24 volts DC, they will run with anything over something like 12 volts. The 24V DC also feeds manual float switches in the tanks that control pumps directly through relays driving 240V AC.

Hi John, how did you get on with putting the sensors into the water tanks? I’ve been finding it tough going to find out from the sensor manufacturers if they can offer certification for potable water usage.

I am looking at a domestic project for when I get down to Australia next month for a monitoring system for home water tanks. Australia has much higher standards to follow than what I am used to for the last 15+ years here in Indonesia so I want to be sure to do the right thing.

Most of the sensors I found are used industrial units good for potable water, some are intended for dry storage but work fine with water, ali-express has a number of new “waterproof” units. Get one with the correct range, and be aware about the blind spot up close to the sensor - the “HDL- 700 B1” unit on ali-express has a blind distance of 3-6 inches. I mount them to the top of the closed tank, and the blind spot isn’t an issue because I have a high level pump shutoff that leaves a bit of room at the top of the tank. But make sure the blind spot isn’t too large, the model “TLCMP70FT” ($125US) on ebay and ali has a blind spot of 0.6 meters, probably too much for this application. Looking at ebay, the used industrial market for these things seems to have dried up, and the few used ones on there are quite expensive! I got a $1,000 unit for around $100 or so a few years ago. Note these sensors mount outside of the tank on top, using a through hole fitting on the top of the tank so they should never touch the water in the tank. Once installed, you program the range into the unit to get a nice voltage variation on the 4-20ma circuit. Using 4-20ma sensors allow you to run whatever length of wire from the tank to the micro, which can be in the house, and you’ll still get an accurate reading. As I run pumps off the levels of the tanks, I chose to also go with float switches which manually cycle the pumps, and use the transmitters to provide feedback on tank state. But I could have gone with just the transmitters, driving the pumps with the micro, but with no redundancy.

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Thanks for the reply. The sensors themselve are good for potable water as all parts touching the water are usually stainless steel, 304U or 316L. It’s the cable outer jacket and any potting compound around the sensor cable entry that is the concern. Some materials leach into the water hence are unsuitable for potable water usage. The ones I use direct from China come with a PTFE jacket which is food grade safe. They cost around $130 but are of excellent quality.

As this will be a commercial product, second hand sensors are not suitable and radar or echosound types are too expensive. Pressure sensors are fit and forget and I’ve had long life in the past with them. The only ones I get failures with are on hydraulic systems with pressures of 3000 to 10000 PSI and high pressure pulses. For level, no single failure to date (7+ years) for some 100+ sensors installed in diesel tanks.

Are they accurate enough Dave for driving things like pumps for tanks less than 3 meters deep? A low level shutoff in a tank could be 4-6 inches above the bottom, which isn’t much pressure…

We were able to measure to 1mm accuracy with these sensors in diesel tanks. They can measure as soon as they hit the water so getting down to 4-6 inches (100mm) is not an issue. Water tanks being stationary don’t suffer from sloshing either so we get a stable reading.