Precision Load Cell (Wheatstone Bridge) Simulator

[Kleinstein]

The LTspice and Kicad plans don't really match. The Kicad one has the 10 ohm resistor upper end wrong.

The circuit does not really need supper stable resistors. As a simulator the circuit is in a way that the resistor drift has rather little effect - much less than the resistance in a real bridge.
Normally just 25 ppm/K resistors should be good enough in in most cases. With 10 ohm the layout part can also be relevant.
When the pot is used to trim the scale factor, there is no longer the need for low tolerance for most of the resistors (maybe still the 10 ohm). Trimmers also tend to have a rather poor TC, so ideally one would avoid them and maybe have 1 selected resistor for the trim instead.

[hozone]

Thanks!

Fixed the KiCad schematic. Added a Calibration resistor instead of the trimmer.
Because 0.1% does not costs a lot more, I think I'll go for 0.1% +25ppm, just to trim less All resistor will be 0805 SMD.
If all ok I'll move to layout and post there if this schematic seems ok to you.

[Kleinstein]

The circuit is still missing the output resistors (175 or 170 ohm). Ideally one would add separate resistors for the different settings (more with the 0 and less with 2 mV/V) to compensate for the extra 10 ohm resistors.  I would also expect to have a switch setting also for 0.
The scaling should not be fixed mV steps, but more in mV/V of excitation.  With the current values one may get it about rigth, though rather large effect for R_cal.

[hozone]

Thanks,

- added SIG+ as step (gain*VExc)
- added output resistor, it should match the 175 + 175 output

As for the switch settings for 0, what do you mean?

[hozone]

Find the PCB attached. Note that there is no ground plane. Don't know if it's better to put one.

[floxia]

How did it perform? I am considering to give it a go!

[hozone]

I'll test it the next week.
Anyway I've yet made a couple of changes. Like adding a fixed calib SMD resistor of 23R7 insted of the THT. And a toggle DPDT to invert the EXC without disconnecting the cables. This is usefull to simulate the "unload" of a load cell.

[tmd63]

I know this is a bit late in the day but have you tried to simulate it on https://www.falstad.com/circuit/ ?
I find the visual simulations work really well.

[hozone]

Thank you for suggestion.
I know falstad.com but I've simulated it in LTSpice, that is a little better than falstad.com
You can find the LTSpice simulation file above in my posts (it's the .asc file).