Zener current goes right from +6V through bridge diodes.
Sense nothing:
View attachment 207293

I am trying to solve this problem.

Darn! ... thanks for enlightening me ... I'll keep thinking about this too. Many thanks!

EDIT: But wait ... why would any current flow through the upper left pFet when it's actually turned off? Also ... I've just noticed that the circuit doesn't work when it's powered by the upper right and lower left Fets

 

This circuit works both ways, but the comparator's power is constantly on. I'd like to come up with something that consumes zero power until the motor is switched on:

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This is your first circuit, in a format that's easier for me to read:

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It works perfectly both ways. It's only drawback is the power being consumed through R2, D1, D3 and L2 even when it's switched off.

 

Darn! ... thanks for enlightening me ... I'll keep thinking about this too. Many thanks!

EDIT: But wait ... why would any current flow through the upper left pFet when it's actually turned off? Also ... I've just noticed that the circuit doesn't work when it's powered by the upper right and lower left Fets

I think I understand now what you meant by "sense nothing" ... it means that the zener current interferes with the circuit's sensing purpose. Right?

 

There you go, I believe I have solved it.

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The following diagram is exactly what I have already built, with the added components for motor rotation (or rather brush commutation) sensing. I managed to import the spice model for the exact nFets and pFets that my circuit uses, so I'm pretty confident it should work in real life. Also, the circuit should consume zero power when the motor is not energized. This because it only rotates when either the CW or the CCW outputs from the MCU are high. And there is no current flow anywhere in the circuit when they're low.

Any comments?

 

Nope ... the previous circuit does not really work. The nFet remains high even when the transients source is removed. It's much easier to use a bipolar transistor instead of an nFet, because the former must be driven by current instead of voltage.

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Anyway, I also solved the power drain problem when the circuit's turned off, simply eliminating the 3.3V source and using the H-bridge driving signals instead. I have thorough tested it and it works fine. The way to test it is by simply removing both S1 and V3, which are the sources of the transients produced by the motor's brushes' commutations in the simulation. And when that is done, the "to_MCU" output remains low when the sim is ran.

 

Variant with motor current monitoring.
No current consumption when motor off or MCU sleep.

 

Variant with motor current monitoring.
No current consumption when motor off or MCU sleep.
View attachment 207411

Nice ... so basically, instead of monitoring if the motor is rotating, this circuit senses an over current condition. Right?

 

Nice ... so basically, instead of monitoring if the motor is rotating, this circuit senses an over current condition. Right?

Yes, when motor is stall it is always over current.
And pay attention to comparator feeding - from MCU logic signal (OUT).

 

Variant with motor current monitoring.
No current consumption when motor off or MCU sleep.
View attachment 207411

Danko, can you post the file of this circuit so I can play around with it a bit? Thanks!

 

Danko, can you post the file of this circuit so I can play around with it a bit? Thanks!

Here it is.
Play without capacitor C1, because of possible deviation in trigger current value
(only in simulation).

 

Here it is.
Play without capacitor C1, because of possible deviation in trigger current value
(only in simulation).

Thanks! ... are you saying that I shouldn't use C1 in the real circuit?

 

Thanks! ... are you saying that I shouldn't use C1 in the real circuit?

In real circuit you should use C1 for eliminating pulse noise from motor.
But in simulation motor current depends on time, so R3,C1 delay will affect
on trigger current value.

 

There you go, I've adapted your new idea to the old circuit, and it works.

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But I think I'll maybe stick with the previous one. Why? Well, maybe I failed to mention this, but the device runs on batteries. So what happens when the batteries go low and the motor stalls without ever drawing over current? ... wouldn't the noise detecting circuit be better for this purpose?

 

But I think I'll maybe stick with the previous one. Why? Well, maybe I failed to mention this, but the device runs on batteries. So what happens when the batteries go low and the motor stalls without ever drawing over current? ... wouldn't the noise detecting circuit be better for this purpose?

You are right, but we do not know so far, are these REAL PULSES
powerful enough to open transistor Q1 in THIS CIRCUIT or not.
So, this part of circuit needs to be prototyped:

 

You are right, but we do not know so far, are these REAL PULSES
powerful enough to open transistor Q1 in THIS CIRCUIT or not.
So, this part of circuit needs to be prototyped:
View attachment 207464

Yes, there is only one way to find out... thank you so much, my friend. You've been of enormous help.

I'll do some experimenting and I promise to be back next week with the results.

 

A brief note: I just ran the simulation using a 4.5V source instead of 6V. That is, I simulated it being powered by three batteries instead of four.... it ran with perfect results.

 

How did this become so complicated?

The H-bridge is already a full bridge rectifier of sorts and the 200mA motor can handle a smallish current sense resistor (0.5ohm to 1 ohm) without losing much drive voltage. If you really want to protect your circuit from reverse current, add two forward biased diodes in series next to the current sense resistor (as shown) to protect from overvoltage into the op amp and one reverse biased resistor in parallel with the current sense resistor to protect from reverse voltage (Below negative power rail). Then amplify so your microcontroller can see a High level input. Power the op amp with microcontroller level voltage to level shift From the 6volt motor.

 

How did this become so complicated?

The H-bridge is already a full bridge rectifier of sorts and the 200mA motor can handle a smallish current sense resistor (0.5ohm to 1 ohm) without losing much drive voltage. If you really want to protect your circuit from reverse current, add two forward biased diodes in series next to the current sense resistor (as shown) to protect from overvoltage into the op amp and one reverse biased resistor in parallel with the current sense resistor to protect from reverse voltage (Below negative power rail). Then amplify so your microcontroller can see a High level input. Power the op amp with microcontroller level voltage to level shift From the 6volt motor.

View attachment 207878

Interesting, I'll give some consideration to your suggestion. Although this sort of circuit is good for detecting an over current condition, and not to check if the motor is rotating or not. Of course, over current implies motor stall, but not always. Also, there's the fact that the motor's coils resistivity changes when they heat up, and so the "calibrated" maximum allowed current changes too.

 

You are right, but we do not know so far, are these REAL PULSES
powerful enough to open transistor Q1 in THIS CIRCUIT or not.
So, this part of circuit needs to be prototyped:
View attachment 207464

I built it ... and tested it ... and it DID NOT WORK...

And then I found an error in my code ... so I corrected it, and tested it again ... and it STILL DID NOT WORK! ...

And then I changed R2 to 330k (because I don't have 300k resistors with me) ... and sure enough, this time IT WORKED!!!!

Thank you oh so very much, my friend. Thanks to you, and every one else who's helped me in this little project, I'm well on my way to a finished prototype.