Sound sensitive vibrating motor

Thread Starter

nickrolfe

Joined Sep 22, 2020
5
Hi,

I'm very new to electronics, so excuse my basic questions and circuit.

I'm trying to create a circuit that will cause a vibration motor to vibrate Proportional to the volume of sound entering the microphone. I've used the attached circuit using an lm386. The circuit works, however the vibration is very weak and only vibrates for loud sounds. The gain of the opamp is 200 (the max) so how do I basically increase the gain more.

Nick IMG_20200921_185108.jpg

Any help would be appreciated.

Thank you.

Nick

Moderators note : rotated and resized image
 

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Alec_t

Joined Sep 17, 2013
11,640
Welcome to AAC!
The only vibration motors I'm familiar with are DC and rotate a shaft with an off-centre weight. They won't do much if fed with AC (via that 1000uF cap).
 

Audioguru again

Joined Oct 21, 2019
1,910
I also think of a little brushed DC motor swinging around a weight.
The "vibration motor" needs to have its sales sheet and datasheet posted here.

I think it is the coil and magnet of an AC speaker without a cone but it vibrates a plate or wall it is mounted on.
Its impedance is important, the LM386 works best with an 8 ohm speaker. Powered from a brand new 9V alkaline battery the output power is only 0.56W at high distortion or is 0.45W at low distortion. Maybe the "vibration motor" needs much more power.

The circuit will not work with a "condenser mic" that must be powered from 48V. Instead it uses an electret mic. The value of 1k for the resistor powering the Jfet inside an electret mic is much too low and makes an attenuator. It should be 10k for much more mic output level.
 

kaindub

Joined Oct 28, 2019
24
Most vibration motors (hepatic feedback) are design to be on or off via the application of a DC voltage. They are designed so at the applied voltage the motors spins at the resonant frequency and hence a large vibration is sensed. At other voltages the resonant frequency is not reached and the vibrations felt are weak.
 
Another output device is the Linear Resonant Actuator (LRA) which behaves exactly like a speaker - it has a 'voice' coil and moving mass in a vertical direction. Google will direct you to sources of LRAs. In my experience they are easy to use and can be driven by TI devises eg. DRV2605 et al. Info on these devices is scarce, but both Sparkfun and Adafruit make driver boards. Your audio circuit needs some work, but you're on the right track! Good luck.
 

Thread Starter

nickrolfe

Joined Sep 22, 2020
5
Welcome to AAC!
The only vibration motors I'm familiar with are DC and rotate a shaft with an off-centre weight. They won't do much if fed with AC (via that 1000uF cap).
The motor i'm using is this one: https://www.ebay.co.uk/itm/Button-Type-Cell-Phone-Micro-Vibration-Motor-Coin-Flat-Pager-Mobile-Vibro/263848868771?hash=item3d6e9e3ba3:g:sRsAAOSwkaxbYByz

Unfortunately it doesn't have much of a datasheet that i could find. I increased the capacitor to 2200uF and there was a marginal increase in the motors vibration, however i didn't notice a difference increasing it past 2200uF. I tried putting a silicon diode in at the end to try and make it more like the motor was recieving pulse width modulated DC, however the motor didn't vibrate at all, leading me to conclude that the voltage coming out must be less than 0.7V. So my thinking is i need to increase the voltage out more.
 

Thread Starter

nickrolfe

Joined Sep 22, 2020
5
I also think of a little brushed DC motor swinging around a weight.
The "vibration motor" needs to have its sales sheet and datasheet posted here.

I think it is the coil and magnet of an AC speaker without a cone but it vibrates a plate or wall it is mounted on.
Its impedance is important, the LM386 works best with an 8 ohm speaker. Powered from a brand new 9V alkaline battery the output power is only 0.56W at high distortion or is 0.45W at low distortion. Maybe the "vibration motor" needs much more power.

The circuit will not work with a "condenser mic" that must be powered from 48V. Instead it uses an electret mic. The value of 1k for the resistor powering the Jfet inside an electret mic is much too low and makes an attenuator. It should be 10k for much more mic output level.
The Vibration motor was bought from here: https://www.ebay.co.uk/itm/Button-Type-Cell-Phone-Micro-Vibration-Motor-Coin-Flat-Pager-Mobile-Vibro/263848868771?hash=item3d6e9e3ba3:g:sRsAAOSwkaxbYByz

There's not much in terms of a datasheet though. I did some tests on the motor though and i calculated the resistance to be 45 Ohms, which is obviously a lot higher than the 8 Ohms of a speaker. And sorry i meant to write electret microphone and 10kOhm resistor on my circuit diagram. I tried putting a silicon diode in at the end to try and make it more like the motor was recieving pulse width modulated DC, however the motor didn't vibrate at all, leading me to conclude that the voltage coming out must be less than 0.7V. So my thinking is i need to increase the voltage out more. Also sorry for the late reply, i was waiting for some more components to arrive and they only just did as i thought the diode would solve the problem.
 

Thread Starter

nickrolfe

Joined Sep 22, 2020
5
Most vibration motors (hepatic feedback) are design to be on or off via the application of a DC voltage. They are designed so at the applied voltage the motors spins at the resonant frequency and hence a large vibration is sensed. At other voltages the resonant frequency is not reached and the vibrations felt are weak.
Yes, this motor is designed for 2.5V to 5.5V and obviously vibrates more with more voltage. However i have tested it at low voltages and it still vibrates just obviously less. The aim is to make it vibrate very small amounts for quiet sounds (so maybe an output of 0.5V for example) and alot for the loudest sounds (for example 5.5V).
 

Thread Starter

nickrolfe

Joined Sep 22, 2020
5
Another output device is the Linear Resonant Actuator (LRA) which behaves exactly like a speaker - it has a 'voice' coil and moving mass in a vertical direction. Google will direct you to sources of LRAs. In my experience they are easy to use and can be driven by TI devises eg. DRV2605 et al. Info on these devices is scarce, but both Sparkfun and Adafruit make driver boards. Your audio circuit needs some work, but you're on the right track! Good luck.
Thank you. Would an LRA be able to work in my analogue circuit though? As it looks like it needs to work with a microcrontroller. Forgive me if i'm being stupid.
 

Alec_t

Joined Sep 17, 2013
11,640
Yes, this motor is designed for 2.5V to 5.5V
It requires a DC supply, not AC (which is what it would get if supplied in your circuit with audio directly or via a capacitor). You will need to rectify the driving signal, and probably also need to use a leaky integrator of the resulting DC so that the motor responds to the envelope of low frequency components of the audio.
 
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