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variable gain current amp

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Kleinstein:
These cheap high resolution panel meters usually use an MCP3421 ADC and µC. So there are not that many parts to drift: mainly the ADC internal reference and the shunt. Both would be relatively small changes in the scale factor, but not offsets. So not a big deal for moderate accuracy over a large dynamic range. There should be low offset drift, which would be the critical factor.

However the ready made panel meters may need an isolated independent supply.

Simon:

--- Quote from: Vovk_Z on May 16, 2020, 09:25:07 am ---It is more repeatable than you can make at home.

--- End quote ---

i am using murata panel meters that cost £25 each. That is why I am trying to come up with the simplest circuitry possible to interface them to a switched shunt. At 200.0mV readout they have done most of the work for me. Speaking to another forum member on the phone last night we figured that i may have been over complicating it for myself as i was not switching the inputs i was trying to just switch the shunt.

If i switch the shunts and switch the inputs to the correct shunt then I have solved everything. I could use mosfets for the shunts and a relay for the meter inputs or an analog switch of a DPDT relay would do it all.

Simon:
Anything stopping me using mosfets to switch my panel meter input locations?

Kleinstein:

--- Quote from: Simon on May 18, 2020, 07:24:51 am ---Anything stopping me using mosfets to switch my panel meter input locations?

--- End quote ---
The supply / common mode range for panel meter could be a factor.

One also needs a voltage (e.g. more positive for an N channel MOSFET) for the gate. A ready made CMOS switch chip may be easier in some cases.

Simon:
No problem there. The sense resistors are on the low side. They are connected to ground via mosfets than switch them on and off. The sense connections go through mosfets practically to ground

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