I have the amplifier shield from this tutorial:
robotshop.com/blog/en/ardui … -lcd-17078
and could not find information about the specific pinout for the 4 pin load cell connector. I measured the voltage across the two outside pins and it appears the left pin is connected to ground, but in the tutorial the positive wire is connected there. Why is red connected to ground and black connected to positive voltage (3.3 I am measuring).
Hi,
You are correct, the load cell wires in the picture from the tutorial are reversed. The pinout of the strain connectors on the Load Cell Shield is as shown in the picture attached.
However, as long as the ordering is respected : GND (Black), Signal -(White), Signal +(Green), 3.3V (Red) or 3.3V (Red), Signal +(Green), Signal (-), GND (Black), this will only reverse the direction of the force sensed on the load cell.
This might be considered when mounting your load cell so that when a force is applied top down, the output voltage of the load cell will increase.
Thank you, that was very helpful.
I have a 100 kg rated load cell
robotshop.com/ca/en/type-s- … 00-kg.html
I am reading the raw a2d value and the highest that it will reach is 667. I am concerned this is because it only being powered by 3.3v instead of 5 (as indicated it should be by the datasheet). Is this possibly the reason it is only reaching 667 on the a2d?
I had to increase the gain by changing the gain resistor on the board in order to decrease the sensitivity and be able to measure the full range of force for my 100 kg load cell. I picked a gain resistance of 330 ohm. Anyone following in my footsteps-- check the tutorial/datasheet for the 2ch amplifier board carefully for the equation to calculate gain resistor and pick your own value.
Here is what you can try to increase the ADC measuring range :
]Change the gain resistor (as you already did). The default theoretical amplifier gain is 495 with a resistor of 100Ohms. With a 330Ohms resistor, you’ll have almost 150 gain (following the formula Gain = (49400/Resistor)+1 provided in this tutorial). Also, please note that the amplifier on the Load Cell Shield will saturate at about 1.8V (when 3.3V powered) due to the 1000Hz low pass-filter in the output./:m]
]Set the reference voltage to 0V using the onboard trimpot of the according channel to measure force on only one way with the full available range. If the shield is powered through 3.3V, and since the output on the analog pin will saturate at about 1.8V, you will have an ADC range of about 0 to 558./:m]
