Motor Controlling Circuit

Exactly what are you trying to do? - stepper motors are fed with steps, not sinewaves, and usually are fed from a microcontroller.

You usually need a translator IC, such as the L297, this allows using a simple step and direction command from the controller.
Also it has sensor inputs from the bridge or motor switching devices, this allows ensuring the constant motor rated plate current be applied at all times, in spite of the higher voltage used for the motor control. .
If under 2a motor current, a L298 can be used in conjunction with the L297.
The circuit you show is not going to cut it.

Nigel Goodwin said:

Exactly what are you trying to do? - stepper motors are fed with steps, not sinewaves, and usually are fed from a microcontroller.

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Hello Nigel,

Yes, stepper motors are fed with steps. Hence, the need for the "interface circuit" which converts the sine wave into a readable signal for the stepper motor. The "interface circuit" will then be connected to a motor driver which then connects to the stepper motor.

They are usually fed from a microcontroller too, however, this project is essentially functioning to do all of the above without the bulk and weight of adding a microcontroller into the design.

Hence, the original question as I'm quite stuck on how I can make an "interface circuit" that goes about performing that task.

ejdwin said:

Hello Nigel,

Yes, stepper motors are fed with steps. Hence, the need for the "interface circuit" which converts the sine wave into a readable signal for the stepper motor. The "interface circuit" will then be connected to a motor driver which then connects to the stepper motor.

Click to expand...

But how?, how does the sinewave convert to steps? - you don't give any idea of what you're trying to do.

ejdwin said:

They are usually fed from a microcontroller too, however, this project is essentially functioning to do all of the above without the bulk and weight of adding a microcontroller into the design.

Click to expand...

What 'bulk and weight'?, it would require less parts than your existing sinewave oscillator, and would only need a similar sized 8 pin chip.

ejdwin said:

Hence, the original question as I'm quite stuck on how I can make an "interface circuit" that goes about performing that task.

Click to expand...

As you don't mention what you want to do, how can we answer it?.

Nigel Goodwin said:

But how?, how does the sinewave convert to steps? - you don't give any idea of what you're trying to do.



What 'bulk and weight'?, it would require less parts than your existing sinewave oscillator, and would only need a similar sized 8 pin chip.


As you don't mention what you want to do, how can we answer it?.

Click to expand...

Hello Nigel, sorry for the vague response.

Essentially, I'm planning for this circuit to power a stepper motor inside a blood rheometer. At the moment, a microcontroller is being used to create the sine wave, turn it into a readable signal to power a stepper motor.

The microcontroller has issues associated with lag etc., and it makes the device more bulkier and not that easy to bring around (reduced portability). Essentially why we want to replace the microcontroller with something smaller, i.e., this circuit. Once this circuit is in perfect working order, it will be constructed as a PCB design and will replace the microcontroller inside the device.

This is where I am stuck, as I have a sine wave producing circuit capable of amplitude and frequency modulation. Since the sine wave circuit produced by this circuit would not power a stepper motor, I want to convert this sine wave into a readable signal for the stepper motor. This is where the "interface circuit" comes in, as I would be unable to plug the motor driver directly to the circuit I have now. Essentially, the "interface circuit" will be interfacing the sine wave generating circuit with the motor driver.
i.e., The sine wave circuit I have now will be connected to the interface circuit, then to the motor driver, then to the stepper motor.
This is where I'm stuck, as I'd like everyone's input on a suitable "interface circuit" I can make.

I hope this clears things up

You're still a bit vague?, are you wanting the stepper motor to speed up and down in response to the position on the sinewave?, or are are you wanting it to just rotate, with the speed based on the frequency of the sinewave?. And what's the variable amplitude for?.

However, whatever the requirement, a microcontroller is by far the smallest, cheapest, and easiest solution - if you've got issues with lag, you're doing something seriously wrong somewhere.

Nigel Goodwin said:

You're still a bit vague?, are you wanting the stepper motor to speed up and down in response to the position on the sinewave?, or are are you wanting it to just rotate, with the speed based on the frequency of the sinewave?. And what's the variable amplitude for?.

However, whatever the requirement, a microcontroller is by far the smallest, cheapest, and easiest solution - if you've got issues with lag, you're doing something seriously wrong somewhere.

Click to expand...

The motor should rotate with the speed based on the frequency of the sinewave. Not entirely sure what the variable amplitude is for, but I'm guessing its something to do with measuring blood flow properties.

Yup, I agree. This is just a project we've been given, so I'm not too sure about the minute technicalities lol.

Hence why I'm trying to find out a suitable interface circuit.

Hope this helps!

What issues would a micro have with lag for a relatively slow pulse? What Micro is it?
One way to produce a continuous pulse that operates every interrupt is the compare function as in the PicMicro range, from the 8 pin up.
If you already have a stepper controller, all they usually require is a square wave (step) signal and a DIR 1 or 0.
Turn the sine wave into a varying rate square wave.

A stepper needs phased signals, eg. typically either four sequential for single-ended drive or two quadrature bipolar signals.

They also need PWM drive and current sensing with feedback, to get anything but fairly low RPM.

A single sine wave just does not fit in with the requirements, in any way that I can see??

As others have said, a cheap MCU such as a PIC will produce any signal needed, including quadrature and they are definitely not "slow" - a PIC16F18313 or 18323 will run at 32 MHz internal clock, and they cost peanuts and take no more space than the opamps and all the other components in your sine wave generator.

The stepper motor itself is the slowest part of a typical stepper driven system, due to its inductance and inertia.

Although If the circuit I have shown or an off the shelf stepper drive, all you need is a dir (1or 0) and a output speed variable freq pulse.
The feedback from the output semiconductors is in order to maintain the motor rated current throughout the RPM range.