BF350 with strain gauge sensor

Other Hardware Sensors
1

Good afternoon,

I am working on my thesis which is basically a study on roll cages, and for this, I need to use strain gauges to take some strain readings. at first, I was going to use strain gauges and a Wheatstone bridge but since I am a beginner I am trying to avoid using multiple components to reduce my sources of error and I found another solution, which is to use a BF350 chip instead.
image

Now for this task I need to use 3 or 4 strain gauges at once, did someone ever work with this chip? any feedback? or any help with the code?

Since I have more than one sample to test, can I change the strain gauge from one chip to the other or should I buy a strain gauge and chip for each test?

Thanks in advance

1 Like
2

If you want to use 3 or 4 strain gauges at once, you should buy 3 or 4 chips and strain gauges. Since the strain gauges are easy to damage, especially if you are removing ad re-applying them, you might need a set of strain gauges for each sample.

3

Thank you very much, that was the plan, what do you think about changing the wire length of the strain gauge? (so that I have equal wire length for each test)
The chip I am going to use is rated for 350 ohms and I only found 200-ohm sensors, is there a way I could go around it?

Thanks

4

Do you have specs on the board?

It looks a little weird to just have a bare 2-wire sensor attached and no wheatstone bridge or half-bridge.

5

This says the breakout board has three resistors that complete the Wheatstone bridge:

https://forum.hobbycomponents.com/viewtopic.php?t=2427
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The OP may find the following helpful:

6

Ah, one might switch one of the resistors out for a 200 ohm resistor that matches the strain gauge.

7

Yes, they are SMT, but that would be possible.

Another peculiarity is that it seems the breakout board outputs an analog signal, 0 to 3.5v dc. It's not clear whether the output is ratiometric with the supply or if it has an on-board stable voltage source.

In any case, I think the OP would be better off with a set of four strain gauges and an HX711 or similar. On the other hand, the OP hasn't said much about the application, so maybe the BF350 breakout would be good enough.

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8

Small update, I found 350 ohm strain gauges :), now I have a problem on how can I make the wire between the strain gauges and the chip longer. Would you think this would affect my readings?

What are your suggestions?

9

Do some simple math:

Use the Wheatstone bridge formula to figure out how the change in resistance in the strain gauge leg (due to the change in wire length) will affect the output.

The possible mismatch between your 350 ohm strain gauge and the completion resistors in the board may have a larger effect.

Neither are likely to be deal-killers, but it would be a good learning exercise to use math to predict the effects.

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10

There's ways to null the differences out, but they mostly work with the other 350 ohm resistance on your strain gauge's half-bridge. Doing a good job nulling out the difference enables you to use higher gains and get greater accuracy, rather than wasting accuracy and range in amplifying the un-nulled constant offset.

11

Good afternoon,

Thank you very much for all your suggestions.

As I mentioned in the beginning I have very basic Arduino knowledge. I was doing some research and found this code. do you think it will work, I imagined that this would require some kind of conversion between what the chip gives to the Arduino and what the strain is.

#define SENSOR_PIN 0
 
void setup()
{
  Serial.begin(9600);
}
 
/* Main loop */
void loop()
{
  Serial.print("Sensor: ");
  Serial.println(analogRead(SENSOR_PIN));
 
  /* Wait 1 second and then read again */
  delay(1000);
}

Now I need to change the code in a way that I could connect 2 sensors with the Arduino at a time. can you please help me out?

Thanks in Advance

12 
#define SENSOR_PIN_A 0
#define SENSOR_PIN_B 1
 
void setup()
{
  Serial.begin(115200);
}
 
/* Main loop */
void loop()
{
  Serial.print("Sensor A: ");
  Serial.println(analogRead(SENSOR_PIN_A));
  Serial.print("Sensor B: ");
  Serial.println(analogRead(SENSOR_PIN_B));
 
  /* Wait 1 second and then read again */
  delay(1000);
}
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13

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