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Double number of pulses per cycle

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engineergc

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Hi,

I will built a circuit to show direction of rotation as CW or CCW.Hall sensors have 120 degree shift.I want to double number of pulses per cycle like below example.In this example hall sensors have 90 degree shift. Therefore by using XOR gates double number of pulses are obtained easily. But in my design, hall sensor have 120 degree shift. How I can obtain double number of pulses? I attached hall signal outputs below.
 

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ericgibbs

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hi,
You can easily double the frequency of a square pulse train, but you not get 120 a degree offset.
What is the range of the rpm you are wishing to measure.?
E
 

engineergc

New Member
I don't want to get 120 degree offset. .There is electrically 120 degrees between hall transitions. How I can double the frequency of a square pulse train without change rpm?
 

AnalogKid

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As with your examples in post #1, you can differentiate both edges of both input waveforms and combine them to get one signal with 4 output pulses per cycle. However, with two input waveforms that are symmetrical (50/50) squarewaves and 120 degrees apart in phase, the pulses in the resulting 4x combined output waveform will not be evenly spaced.

ak
 

engineergc

New Member
Hi Ericgibbs,
I tried to built example in post #4 in LT Spice but I think it can not be useful for me. Because, for example if hall sensor low, because of frequency doubler I will obtain high and low pulses respectively. Therefore with same manner hall2 and hall3 I can not determine direction of rotation.
I will try example in post #6 but I can understood how this circuit is working? Could you explain me working principle of this circuit?
 

ericgibbs

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hi,
I would use 4049B inverter/buffers between the Hall output, so that the pulse signal is High going.
E
 

spec

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Hi,

I will built a circuit to show direction of rotation as CW or CCW.Hall sensors have 120 degree shift.I want to double number of pulses per cycle like below example.In this example hall sensors have 90 degree shift. Therefore by using XOR gates double number of pulses are obtained easily. But in my design, hall sensor have 120 degree shift. How I can obtain double number of pulses? I attached hall signal outputs below.
Hi engineergc,

You can get the 2x signal by simply connecting the A aignal to one input of an exclusive or gate and the B signal to the other input of the exclusive or gate. http://www.ti.com/lit/ds/symlink/sn74ahct86.pdf

spec
 

engineergc

New Member
What are the A and B signals? If A is Hall1 and B is Hall2, when I connect them directly to XOR gate, I can not determine direction of rotation. At the output signal of XOR gate is not useful to determine direction of rotation.
 

ericgibbs

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I will try example in post #6 but I can understood how this circuit is working? Could you explain me working principle of this circuit?
hi,
It is assumed that Hall device hrpm is placed in between Hall h1 and Hall h2 on the rotating body.

If hi goes High first then U1 FF is Set high on the high going leading edge of h1.
This means that the AND gate U6 will allow h1 pulses thru to Set U2 FF High, so that is Forward rotation.
hrpm also Sets U3 FF High, indicating rotation.
As long as hrpm keeps triggering U3 and switching the Gate of U5 N MOSFET the R1/C1 will not be able to Reset U3.

If hrpm pulses stop [ no rotation] U3 will reset,due R1/C1

If the direction of rotation is reversed then U4 will be enabled and U2 will reset to 'rev'.
The hrpm will still trigger U3 High for rotation.

Do you follow that OK.

E
 

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alec_t

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If all you want to do is detect CW or CCW rotation direction then a single D-latch will do the job and you don't need to double the pulse frequency.
CW-CCW-sense.JPG

Edit: a, b and c represent the Hall signals.
 
Last edited:

spec

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What are the A and B signals? If A is Hall1 and B is Hall2, when I connect them directly to XOR gate, I can not determine direction of rotation. At the output signal of XOR gate is not useful to determine direction of rotation.
OK
 

ericgibbs

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hi eng,
This sim plot shows the rpm/fwd/rev/rot signals.
Set the values of R1 and C1 to suit the slowest RPM.
E
 

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engineergc

New Member
Hi ericgibbs;

Thank you for your helps. I tried the circuits that you suggested. But I have a problem. As early mentioned I have three outputs as CW, CCW and rotation. When motor turns to CW, CW ouput must be high and CCW output must be low, vice versa. In simulation I circled signals that they are low at the CW output when motor turns to CW. I want to remove this unwanted signals. I think I can provide onyl high signals at the CW output, by using double number of high pulses per cycle. My purpose like below example except low pulses part. This example is an example of frequecy doubler. Actually frequency doubler could be useful, but frequency doubler gives high pulses both low and high pulses. There is electrically 120 degrees between hall transitions therefore when I used frequency doubler hall 2 and hall3 will give high pulses at 0 ms and I can not determine direction of rotation. How I can solve thsş problem?
Regards
 

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ericgibbs

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When motor turns to CW, CW ouput must be high and CCW output must be low, vice versa.
They are, FWD=CW & REV=CCW
When FWD= high then REV = low and vice versa.

EDIT:

Have you run my posted asc file in simulation.??? POST #13 asc's
Please post the plot.
 

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Les Jones

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I think you need a phase sequence detector. BobW came up with a solution post #5 of this thread. I would add to his idea by using pulse C to clock the state of the first flipflop into a second flipflop. the state of the second flipflop would indicate the direction.

Les.
 

ericgibbs

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hi eng,
I have identified two more signal points on this sim ccg and ccwg, you can see that they are gated to suit the Rev/Fwd signals, no change to the circuit.

As far as I can understand your project description, this circuit is doing what you are asking.?

E
 

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