I'm still struggling to apply my limited knowledge of op amps... so I've created a problem to solve... but need your help.

I can follow along other peoples projects but it quickly becomes apparent that I do not fully grasp the fundamentals when I try and solve a problem of my own.

So here is my own problem I'm trying to solve, as shown below:

I have two scenarios. I think the first one is fairly easy, but it is knowing how to achieve the 2nd that is more challenging, especially if you wish to say use the same op amp and even the same circuit the 1st.

How does one go about this?

As per usual, I very quickly try and over-complicate matters... like when spotting these types... Transresistance amplifiers... and wondering whether I should/could use these...

Anyway, no doubt this is a very straightforward problem for the experts.

I look forwards to getting some tips.

Thanks.

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0 dougw over 3 years ago

Good references. Figure 7 can be modified to use a pot to adjust the offset:

R1 adjusts the voltage swing, R3 adjusts the offset.
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0 BigG over 3 years ago in reply to dougw

Brilliant. Thanks dougw

I provided some detail of me working through that document. Kinda got stuck, but I appreciate your answer.

I was hoping that my two options could be selected through software using same circuit, so not sure a resistor pot will work in this case.
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0 shabaz over 3 years ago in reply to BigG

The op-amp guides are super-useful, but they address op-amps only, whereas your solution could involve other techniques in combination. But, more information is needed (e.g. what is the load, and is your stimulus AC (e.g. square wave or PWM) or will you want the output to work for DC too, and also do you wish the input to take values between 0V and 3.3V (e.g. DAC inside MCU) or is it a digital logic output? (this can affect the design, depends on if you wish to have a linear response, or not).
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0 BigG over 3 years ago in reply to shabaz

shabaz said:
But, more information is needed (e.g. what is the load, and is your stimulus AC (e.g. square wave or PWM) or will you want the output to work for DC too, and also do you wish the input to take values between 0V and 3.3V (e.g. DAC inside MCU) or is it a digital logic output? (this can affect the design, depends on if you wish to have a linear response, or not).

A very valid point. For background, I had spotted the other day a rather unusual signalling design, which is used in electrical vehicle charging controller's control pilot signal wire. This looks to be a PWM generated signal. It is used to communicate charging states between a vehicle and the charging station. I'm not here trying to change the design. I was merely trying to simulate this and learn about op amps at the same time.

Of course, if it could be done another way using an MCU to generate these different signals, I would be keen to know too. For example, I did wonder if RS232 could be used instead.

source: https://www.jsae.or.jp/en/publications/yearbook_e/2014/docu/28_industry_standards.pdf
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0 dougw over 3 years ago in reply to BigG

To control the offset digitally might require another op-amp:

Would you consider using transistors?
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0 dougw over 3 years ago in reply to BigG

To control the offset digitally might require another op-amp:

Would you consider using transistors?
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