Multiplexing 16 strain gauges with only one Wheatstone bridge and one IA

Thread Starter

SteveRS

Joined Feb 5, 2021
15
Hello!
I'm trying to come up with a way that I can multiplex the signals from say, 16 strain gauges. The output of the multiplexer would go to an instrumentation amplifier, and then to an ADC.

Considering that strain gauge signals are in the order of mV's, I am concerned about the inherent 'Ron' of the multiplexer. I am also thinking that the Ron won't matter though? Because the signal is getting boosted by the In-amp
It might matter with the 'flatness' of the multiplexer, but perhaps not because all the strain gauges will be zeroed by their original offset (data-data[0]).

What do you guys think?

Thank you for anytime you can lend to this!
Hey @Rocky_circuits,

I'm trying to do the same thing. Have you find a way to multiplex between the strain gauges ?

Thanks

Mod: Link to old Thread.E
https://forum.allaboutcircuits.com/threads/multiplex-signals-from-strain-gauges.158366/post-1377318
 
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Thread Starter

SteveRS

Joined Feb 5, 2021
15
Hi guys!,

I'm trying to build a circuit to read 16 strain gauges with only one Wheatstone bridge and one IA. I have attached a picture of the circuit I want to design. Is it possible to do that ?
Any help and recommendations will be really appreciated.

Thank you,

SG_circuit.jpg
 

ApacheKid

Joined Jan 12, 2015
385
I'm sure there are ways, of course you'd need to ensure that the reading of the output value was synchronized with the multiplexing of the gauges.

How about something like this:

SN74CB3Q16244

Seems promising to me, sixteen analog channels is supported - see datasheet.

Although it may not support the ability to have just a single switch on at any time, but it may lead somewhere...
 

Thread Starter

SteveRS

Joined Feb 5, 2021
15
I'm sure there are ways, of course you'd need to ensure that the reading of the output value was synchronized with the multiplexing of the gauges.

How about something like this:

SN74CB3Q16244

Seems promising to me, sixteen analog channels is supported - see datasheet.

Although it may not support the ability to have just a single switch on at any time, but it may lead somewhere...
Okay, so if I found the write components this circuit could possibly work ?
 

ApacheKid

Joined Jan 12, 2015
385
Here's the solution:

MUX506

Page 24 of the datasheet starts to explain stuff in more detail.

I'd envisage a 4 bit binary counter running at whatever rate, its 4 bit output would drive the address bits of the MUX so each input would be connected to the single output for some interval, then disconnected and the next one connected, automatically at whatever rate you need.

But I'm looking at this the way I would have in the 1980s when I was more up to date, others here may know better solutions.
 

ElectricSpidey

Joined Dec 2, 2017
1,654
You might be able to do this with one 16 channel digital MUX and two low side 8 channel load drivers if the current thru the sensors does not exceed 500mA.

Otherwise I would consider using one mux and a 16 channel relay module.
 

Thread Starter

SteveRS

Joined Feb 5, 2021
15
Thanks @ApacheKid,
Thanks @ElectricSpidey,

I have found this interesting MUX, would it fit my applications ? I want to read each channel at around 50 Hz
CD74HC4067

Am I asking because , electronics is not my strength and I'm looking for some advices before purchasing the components and start my trials.
Thanks
 

ApacheKid

Joined Jan 12, 2015
385
Thanks @ApacheKid,
Thanks @ElectricSpidey,

I have found this interesting MUX, would it fit my applications ? I want to read each channel at around 50 Hz
CD74HC4067

Am I asking because , electronics is not my strength and I'm looking for some advices before purchasing the components and start my trials.
Thanks
Yep, that device seems to be a good candidate too, I'd grab a 4 bit counter like this for example: 74HC163AP

Fact is though that the entire system needs to be thought through, you're going to have a single output that changes rapidly with different analog values, these being the sampled strain gauge at whatever instant.

How do you make sense of that? whatever is going to consume it needs to be synchronized with the counter.
 
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ApacheKid

Joined Jan 12, 2015
385
Also one could just have a basic MCU board with a simple display, the board would cycle the multiplexer and display each of the 16 voltages on the display, perhaps updating them at like 10Hz or whatever. The board's A/D converter would monitor the output from the bridge...
 

Thread Starter

SteveRS

Joined Feb 5, 2021
15
Yep, that device seems to be a good candidate too, I'd grab a 4 bit counter like this for example: 74HC163AP

Fact is though that the entire system needs to be thought through, you're going to have a single output that changes rapidly with different analog values, these being the sampled strain gauge at whatever instant.

How do you make sense of that? whatever is going to consume it needs to be synchronized with the counter.
Okay, so the counter is necessary to loop through the mux channels? I was planning to use an ARDUINO Uno for that, or it is not precise enough ?
 
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