Hi

I think that your first instinct was right, you must be draining too much power from the DAC, but you should still verify that. Try placing resistance at the output and measure the voltage. Look in the output impedance of the DAC and see that it respect the voltage divider.

As for the follower circuit, make sure that is has a nice clean voltage supply, and don't use a 741 OP-AMP, this hardly work in the lab, so it has a hard-time in real-life.

Finally, make sure that the frequency of your DAC is well within the bandwidth of the OP-AMP

Good luck

Hello Luc-Andre Gregoire ,

Thankyou so much for your valuable suggestion.

I found the error, it was because i was not using the default pin for the amplifier output. As a result a Zero Ohm resistance was not possible.

Every DAC has an output impedance (larger or smaller), unless it has an output buffer (amplifier). Choose a buffered DAC or add a simple opamp repeater at the output. Take care to keep de output frequency in the limits supported by the opamp (fT frequency)..

Reading "bridge" I immediately thought of "strain gauge" bridge. If so: these are really low-resistance - thus you'll need a really capable OpAmp to drive it. Check for the bridge resistance and find an OpAmp with low noise, capable of driving the bridge resistance.

@Vasile (and the rest)

Muhammad already found out that driving his bridge is not trivial. Besides all other flaws the 741 is not capable of driving low-impedance loads. Short circuit current: max. 40 mA (741A - later types drive less).

Hello Muhammad,

How are you? Kindly recall my earlier responses to your questions when you had asked whether to drive you bridges or (strain gauges) with a DDS or so. And I had also suggested that use a Wien-Bridge Oscillator with a driver. So here you are!

Kindly note that the strain-gauge bridge is as good as a low-power electronic circuit in terms of its current hungryness!!! You need a complimentary transistor pair to drive the bridges. I know it is not one or two but you are driving as many as 30 bridges. Treat this as a HEAVY LOAD and instead of a passenger car use Big Lorry to carry the load!!

What I mean to say that as you are generating your sine wave from the DAC, buffer it with suitable op-amp and then use a transistorized drive circuit to BOOST the current like a POWER AMPLIFIER.

I hope now your strain gauges will be relieved out of strain and will start "Obeying your order" (read "working the way you want them")!!!

Looking forward to hear from you positive again!

Once again All the best!

Hello Muhammad,

your problem probably comes from overloading the ADC by the bridge. Each voltage source has its internal resistance, which creates the voltage divider with the load. If this internal resistance is not negligible comparing with the load, then the output voltage can drop too much. The only solution of this problem is to place the voltage follower between the ADC and the bridge. Use the amplifier with low input voltage and current offsets and take care of the proper grounding of the circuit, eventually use the filter narrowing the trace bandwidth to prevent parasitic noise.

Good luck

Ivan.