pwm & variable amplitude i/p getting analog average I drawn readout

Thread Starter

Poor old sod

Joined Jul 25, 2017
78
Still on this old Gopher problem. Now have op amp NE5532NP, 8 pin DIL chip.
0-80mV PWM input and 220 Ohm 1mA fsd meter.

Will set gain at -2.5. Have 0-12V and 0-24V power avail.

have IC socket and small prefab cct board from Altronics.

8 or so 5K 1/8W resistors.

running out of data quota-pls advise chip pinout, do I need to provide center tapped Earth from power supply, which ps to use and a schematic--I've forgotten all this stuff. Zero error correction not required.
 

ebeowulf17

Joined Aug 12, 2014
2,945
Still on this old Gopher problem. Now have op amp NE5532NP, 8 pin DIL chip.
0-80mV PWM input and 220 Ohm 1mA fsd meter.

Will set gain at -2.5. Have 0-12V and 0-24V power avail.

have IC socket and small prefab cct board from Altronics.

8 or so 5K 1/8W resistors.

running out of data quota-pls advise chip pinout, do I need to provide center tapped Earth from power supply, which ps to use and a schematic--I've forgotten all this stuff. Zero error correction not required.
Is this a continuation of this thread?
https://forum.allaboutcircuits.com/threads/how-to-digitally-measure-avg-current-drawn-by-gopher.145102/#post-1235978

Assuming yes, what have you done since the last discussion there? Have you tried the basic RC filter approach? If so, what sort of results did you get? What's making you want an op amp solution, and what exactly are you wanting the op amp to do?

Also, have you changed the meter and/or burden resistor that you're planning to use?

I'm a little lost here. Maybe I'm misreading something or referring back to the wrong thread... or maybe I'm just too sleepy to think straight!
 

Thread Starter

Poor old sod

Joined Jul 25, 2017
78
yes, same thread. tried 1uF and 15K resistor--better, but still very erratic readings. Could use longer T. Just think that analog meters read average, and if I use the op amp to increase the i/p voltage to something easily readable, will get a fair result, no synch required Altho' the pwm proportion is usually infrequently adjusted, the actual instantaneous current drawn varies with load. I want to display a real time average of the instantaneous currents.

NB I've just replaced the wig wag pot with a non sealed unit [$16-], and I'll increase the maximum available speed from 6.x to 10 kph after I get the meter working. Meter is 45x20mm(?), hope the rough paths don't wreck it too soon.
 

ebeowulf17

Joined Aug 12, 2014
2,945
yes, same thread. tried 1uF and 15K resistor--better, but still very erratic readings. Could use longer T. Just think that analog meters read average, and if I use the op amp to increase the i/p voltage to something easily readable, will get a fair result, no synch required Altho' the pwm proportion is usually infrequently adjusted, the actual instantaneous current drawn varies with load. I want to display a real time average of the instantaneous currents.

NB I've just replaced the wig wag pot with a non sealed unit [$16-], and I'll increase the maximum available speed from 6.x to 10 kph after I get the meter working. Meter is 45x20mm(?), hope the rough paths don't wreck it too soon.
Gotcha - I think I understand what you're going for now, but I'm not sure how well it will work.

As for your original question, here's the pinout:
IMG_4636.PNG

The problem I see with this plan is that you're trying to amplify a very small voltage close to your supply rail. The op amp you mentioned does not appear to be rail-to-rail, which would mean it doesn't stand a chance in this application unless you can provide the negative side of a dual supply to power it. In other words 12V or 24V and ground (circuit DC common, whatever you want to call it) won't do you any good, because with that as your power supply the input range of your op amp starts at 1-2V, way above your 80mV input signal.

With a rail to rail op amp, the basic concept might work, but even R-R models have minimums, and I'm afraid 80mV is gonna be challenging without a dual supply.
 

Thread Starter

Poor old sod

Joined Jul 25, 2017
78
I can center tap the two batteries to get +-12 to 15V, but then I have to place the shunt at an end of the battery chain. I can adjust the zero point by referencing if an input is power rail voltage and the other just below it? which one should be inverted i/p? can I use the opposite rail voltage from the shunt for referencing without a short? I'm thinking a fixed ref voltage might not work well as batts discharge. If I could use an existing terminal voltage for Vref that would help. it is a dual package, I may need to use the other op amp too? the data sheet gives suggestions for buffering and referencing. of course, I could use more gain and damp down on the meter, but I see no immediate advantage.
 
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