Short video about this device:

0:00 - description.
0:23 - usage for simple weight scale application.
1:03 - usage for Automated 3-axle Truck Weight Measurement System.
2:47 TODO list
3:00 What next?

Where load cells mainly use in industry?

Trucks weight scales
Railway weight scales
Conveyor weight scales
Cranes

Attention, please! Just push "read more" for the project details, and you will find a lot of useful information about the device development!

In the project log, you can find my implementation of weight scale for 3 axle trucks, and some tests.

I apologize for my bad English. Please, be patient to this fact, or show me errors, I will fix it)

I will try to post new chapter every day, but sometimes it is impossible, because I have one more large project and I need to spent some time for it. If you are interested here the link - https://hackaday.io/project/166617-ioton-micrio .

Let's start.

About the load cells:

Because of my bad English I will not write about load cell working principles and theory behind it (you can find enough information about it in the internet).

I stops only on weaknesses.

What weaknesses the load cells have?

1. Low sensitivity (typically around 2mv/V). With 5V excitation voltage, we will get only 10mv for tension and the same voltage for compression. So the noise immunity is not good, and we cannot use a long cable between the load cell and the ADC.

2. High temperature drift. If you put the same load on load cell you will get different results for different load cell temperatures. Also, the temperature affect on two parameters - zero balance and sensitivity balance.

About the solutions on market:

What imperfections in design for typical solutions I found on the market?*

Most of the load cell to Modbus interfaces have DIN rail mount for mounting in the electrical enclosure. In most cases the distance between load cells and electrical enclosure is significant, so noise immunity of this system is bad and we cannot do precise measurements.
All solutions I found on market cannot do anything with the load cell temperature drift.

Project Logs

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My converters for MOTORSPORT
Andrey V • 09/05/2019 at 12:28 • 0 comments

Some time ago I did a presentation about load cells used for interactive suspension loads measurements. I showed it three times and haven't had any feedback. The idea is simple:

But today I received a letter from one Motorsport team about cooperation ability in the field of suspension test and measurements. It's very low profit project, but I think life is not only about money.

This project has some challenges. At first, I need custom load cells to install if directly in suspension. I have some thoughts about it and I filed a patent application (I will publish it if I will get patent pending).

The load cell must be from titanium alloy to minimize weight. Also, it must have a specific form.

Also, I will need to change PHY and protocol from RS485 and modbus to CAN (for direct connection to the car) and Serial (for using with the radio transmitter). And make some more minor changes.
Read more »
PRELIMINARY TEMPERATURE DRIFT TEST
Andrey V • 08/29/2019 at 07:52 • 0 comments

Yesterday I did preliminary load cell temperature drift test.

Here my test setup:

I understand it's not so accurate setup for measurements(I need thermal chamber for accurate measurements) , but let's look on the results:

Read more »
PCB zones
Andrey V • 08/27/2019 at 15:56 • 0 comments

When I'm developing PCB, I decided to split the PCB into 4 main zones, absolutely symmetrical from both sides:

It was a little bit challenging to provide proper grounding w/o undesirable current paths. I did some minor mistakes with the grounding in REV 1.0 but I think I fixed it all in REV 1.1.

Also, the additional spacing between unisolated GND and isolated GND was added.

I used 0603 parts (minimum size) for hand mount ability. Unmounted parts - temperature sensor(U9).
It's time to swim.
Andrey V • 08/21/2019 at 17:53 • 0 comments

For outdoor usage, I need to make some tests.

At first, my device must take a bath.

I can't do complete IP68 test right now, but I will do it later.

I think I leave it in the glass for one night with logging sensor data.
ADC NOISE & SENSOR NOISE
Andrey V • 08/20/2019 at 18:58 • 0 comments

Some measurement of sensor and ADC noise.

I wrote a simple software to measure sensor noise and get the noise-free count.

Test setup:

Left to right: 0.2ton Load cell, my Load cell - Modbus interface, IOTON MICRIO MPU & DI8 input module.

500 counts noise video:

As you can see, I have around 120 counts of noise Peak-to-Peak.

Lets calculate the counts... 24bit = 2^24 = 16 177 216 counts. Noise of my system = 120 counts. So I will have 16 177 216 / 120 = 134810 noise free counts, it's around 17 bits. Not so bad.

For 200 kg load cell (actually it's 400 kg load cell, because 200kg for compression and 200 kg for tension) I will have an accuracy of around 200 000 * 2 / 134810 = 3 gram.
TEST SETUP hardware completed.
Andrey V • 08/19/2019 at 11:19 • 0 comments

1, 2, 3, 4, 5, 6. Independent weight scales. Each consists of the load cell and Load cell - Modbus converter (PCB w/o housing)
7. DIN enclosure with Raspberry PI3 B+ inside.
8. IOTON PI-FACE (my interface for Raspberry PI with RS485, RTC, UPS, power controller, WATCHDOG, GPIO connector for modules e.t.c.)
9. IOTON DIO4.1 (my universal isolated I/O module)
10. OMRON E3S-X3CE4 (photoelectric switch)
11. LED traffic light for the driver.
12. IP camera for the license plate recognition.
13. Truck model (I need to add one more axle)
14. Interchangeable license plate model.
TEST SETUP. UI minor modification.
Andrey V • 08/18/2019 at 19:41 • 0 comments
Added:
- Total load gauge.
- Traffic light.
- Dynamic change for gauge max load and color signalization.
TEST SETUP IP camera for license plate recognition.
Andrey V • 08/17/2019 at 13:23 • 1 comment

Just finished IP camera mount for license plate recognition.

I used IP camera module, therefore I need some mounts for it. So I did it on my home CNC from the acrylic glass.

The mount drawing:

Mounted camera:

Read more »
UI for TEST SETUP
Andrey V • 08/16/2019 at 08:53 • 1 comment
Preliminary version of UI for the test setup done.

It takes more time then I expected (around 14 hours).

It looks ugly, but I think functional enough.

Measurement tab:
- Load gauge for each truck wheel
- Total truck load
- Overload/underload data and signalization for each axle.
- Max load field for each axle (kg)
- Load difference field for each axle (%)
- Load difference error indicator for each wheel
- Numberplate/ Vehicle type - for use with numberplate recognition system and vehicles database.
Unloaded:

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TEST SETUP. SCHEMATIC AND WIRING.
Andrey V • 08/15/2019 at 07:13 • 1 comment

SCHEMATIC

The schematic of my test setup is quite simple:

WIRING

It's also simple, I did it in around 30 minutes. It's no problem to connect cables to the powered device, it's only 24V and has protection and galvanic isolation for any inputs, outputs and data lines (like RS485 PHY).
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