[Help] DC Electric motor Frequency controller circuit.

[Sephtor]

Hello Everyone

I am currently building a vibrational component for a project of mine. Here is what im trying to do and hopefully you guys will be able to help me out.

I am trying to build a circuit in which a small DC electric motor is being powered by 2 AA batteries.

I want this motor to vibrate at 3 different frequencies and i would like a sensor to test if the frequency of the motor dropped to a certain point as the batteries deplete. If the frequency drops to a certain point then a red LED would turn on indicating that the frequency is below the threshhold frequency.

My first thought is using a microcontroller however i have not done any programming on a microcontroller before and would like to know which ones would be a best fit?

The microcontroller would only need 2 output pins (1 driving the motor at a certain frequency and 1 turning the red LED light on when it drops below threshold frequency) and 3 input pins (1 for the power supply which would be 3V..or i can attach a boost converter if i need to have it at 5V, 1 for recieving data to check if the compact electric motor dropped below a certain frequency and 1 for sensing the offset at how much the frequency dropped so that it could drive more current through it to make up for that offset when the batteries deplete)

Yes the device is going to be handheld and no its not a vibrator haha

If there are other circuit elements that can do the job the microcontroller can then please suggest them.

I would greatly appreciate your help. I am new at this and would like to know where to start.:?:

Thank You in Advance.

Best Regards

 

[kender]

Here are a few thoughts:

- Vibration can be sensed directly with an accelerometer.

- Vibration frequency will be the same as the revolution rate of the motor. So, you could add a tachometer to the motor. Are you using a pager vibrator motor with eccentric weight? If so, the weight is probably made of steel, and you could detect it's revolutions with hall-effect sensor. Of course, there are other types of tachometers too (e.g. optical).

BTW, here's another good place to ask sensor-related questions: **broken link removed**

 

[Sephtor]

Thank you kender i will look into that.

The motor i am powering is a Brushless DC motor (the kind you find in toothbrushes)

I have the following goals

Goal:
1) Operate at 3 user set values of constant RPM
2) If the rpm drops due to the batteries weakening, either boost the voltage to keep it constant through a feedback loop or turn on red led indicating that a change in batteries is required.

it is very important that the motors rpm does not drop from the user specified values

Attached are my designs... I have 2 AA batteries powering a microprocessor unit which controls the rpm value which can be set using pushbuttons.... the microcontoller powers either a crystal oscillator or a BJT which provides current to a frequency to voltage converter( in case a) or a resistor (in case B)...if the current/voltage drops below a certain level then the microcontroller either supplies more or turns the red LED on.

Is my design Viable? Is there a more efficient design which i could implement which can be more cost effective and require less components? Any help will be greatly appreciated