Here's a little project that I made that may be a bit laughable for the real experts in this forum, but that came in pretty handy for me when I was trying to measure current with an oscilloscope.
What it is: It's a little circuit that makes it easier to measure current with an oscilloscope.
What it does: It subtracts the voltage offset from the signal being generated by an ampsense AMP25 sensor so as to bring it within range of the oscilloscope.
Why: Because an AMP25 sensor generates an output signal between 0 and 5V depending on the current that passes through it, but it has a 2.5V offset. That means that negative current values will be reported as a voltage between 0 and 2.5V, and positive values will be reported as a voltage between 2.5 and 5V
Why is this an issue?: Because oscilloscopes can adjust for signal offset only within certain limits, and if I want to read a small current signal (like when the AMP25 reports a value of, say 25mV) then I will run into trouble. For example, to more or less accurately read 25mV, the oscilloscope's vertical divisions should be set to 10mV. But since my oscilloscope has only 8 divisions in its complete screen, and the middle of the screen is 0V, then the maximum offset that it will let me adjust at that scale is ±100mV... but the problem is that the AMP25 zero-Amp signal is reported as 2.5V, which is way above the maximum 100mV that the oscilloscope will allow me to offset adjust on the 10mV/division selected scale.
So without much further ado, here's what I did: I built a simple, adjustable voltage subtractor circuit that subtracts 2.5V from any voltage entering it, conditioning the AMP25's output to make 0A = 0V ... and now negative current values fall in the range of -2.5V to 0V, while positive ones are in the range of 0V to +2.5V
The circuit is powered with a standard wall-wart set at 12VDC output. This voltage is then lowered and regulated to 5V with an off-the-shelf 7805. After that, I used an ICL7660S chip configured so that it generates -5V from the 5V being fed into it. This allows us then to power an OpAmp (I used an OPA244) configured as a voltage subtractor. A simple 50K trimpot connected as a voltage divider serves as an adjustable 2.5V reference for the OpAmp.
What it is: It's a little circuit that makes it easier to measure current with an oscilloscope.
What it does: It subtracts the voltage offset from the signal being generated by an ampsense AMP25 sensor so as to bring it within range of the oscilloscope.
Why: Because an AMP25 sensor generates an output signal between 0 and 5V depending on the current that passes through it, but it has a 2.5V offset. That means that negative current values will be reported as a voltage between 0 and 2.5V, and positive values will be reported as a voltage between 2.5 and 5V
Why is this an issue?: Because oscilloscopes can adjust for signal offset only within certain limits, and if I want to read a small current signal (like when the AMP25 reports a value of, say 25mV) then I will run into trouble. For example, to more or less accurately read 25mV, the oscilloscope's vertical divisions should be set to 10mV. But since my oscilloscope has only 8 divisions in its complete screen, and the middle of the screen is 0V, then the maximum offset that it will let me adjust at that scale is ±100mV... but the problem is that the AMP25 zero-Amp signal is reported as 2.5V, which is way above the maximum 100mV that the oscilloscope will allow me to offset adjust on the 10mV/division selected scale.
So without much further ado, here's what I did: I built a simple, adjustable voltage subtractor circuit that subtracts 2.5V from any voltage entering it, conditioning the AMP25's output to make 0A = 0V ... and now negative current values fall in the range of -2.5V to 0V, while positive ones are in the range of 0V to +2.5V
The circuit is powered with a standard wall-wart set at 12VDC output. This voltage is then lowered and regulated to 5V with an off-the-shelf 7805. After that, I used an ICL7660S chip configured so that it generates -5V from the 5V being fed into it. This allows us then to power an OpAmp (I used an OPA244) configured as a voltage subtractor. A simple 50K trimpot connected as a voltage divider serves as an adjustable 2.5V reference for the OpAmp.
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