Load sensor and amplifier

Hi All, I'm trying to get a weight measurement working with my current project and i've hit a brick wall :(

I have a pair of SEN-10245 and a ina114bp amp as in the video below:

https://www.youtube.com/watch?v=Bm6ANv93YjM

The sequence of the wires is different on each load sensor. Black,white,red vs white,black,red -> I'm not sure if this is significant.

The circuit is black of each sensor to gnd white of each sensor to 5v red of each into V_in- and V_in+ of amp

amp_ref to gnd V+ to 5v V- to gnd v_out to arduino analogue pin

between rg and rg is 5ohms for the gain setting.

I can't get any meaningful output on the reading. Seams to sit at 140 (of 1024) in the adc reading.

Any advice to making this work?

Thanks, Isaac

You probably have an offset voltage that needs trimming out. What gain are you using?

Per MarkT’s comment, any offset in the cells – and there’s always some offset – is going to be overmagnified by your 5ohm / 10K gain.

The comments on Sparkfun’s page suggest the gain should be around 1K (50 ohm resistor). But, anyway, what it really comes down to is tweaking that gain resistor: use a ~100 ohm pot and, without any load on the cell, watch the readings change as you adjust that pot. The value should sit around 512 (per the Arduino analogRead()) when the gain is too low/resistance too high and then when you pass the sweet spot it’ll jump down to 140. Back it off a bit and then try stressing the cells to see if the readings are good.

Google “HX711” modules if you’re looking for a better option than the INA114. The HX711 is a digital output with 24bit precision; it’s not just an amplifier like the INA114. The Arduino’s 10bit, 0 - 1024 range is kinda pitiful compared to the 24 bits or 0 - 16 million range with the HX711.

Gain is 10k with 5ohm

Okay, shall give that a try :) Thanks both for the input.

How significant are the colours of the wires in this case? Should I take the middle as the sense line and the other as the excite?

Cheers, Isaac

If you measure the resistance between the three wires then white-to-red and red-to-black should be equal and white-to-black will be double that resistance.

Your whites are "excite +" and blacks are "excite -" and the difference in the output between the reds is your weight measurement.

Good info. Thanks Chagin.