Maker Pro
Maker Pro

Vibrating Metronome Project

raehunt12

Nov 10, 2016
2
Joined
Nov 10, 2016
Messages
2
New to the forum here. Hope Im posting to the right area. I am a runner and try to follow a 180 SPM run cadence. I want to design a vibrating metronome that will fit into the casing of a watch to be worn while running and not disturb other runners with an annoying beep. I have been doing some research and am not sure if this project will be possible. I am thinking if it is possible I would use a 555 IC. I would also like to keep a small battery (possibly 3v) that will fit inside the case of a watch. Im not sure if this will be possible due to the current requirements of a vibrating motor.

If anyone could guide me in the right direction of how to figure this circuit out or if its even possible that would be great!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
Sure, 180 per minute is 3 per second. A 555 can easily operate at that frequency.

If you can get hold of a small vibrator motor, you could set up a 555 that is on for 200 to 300ms and off for maybe 50 to 100 ms. Turn the motor on when the 555 is off (output low).

You will probably want to be able to adjust the frequency somewhat.

Then you'll have something which briefly vibrates about 3 times per second.
 

raehunt12

Nov 10, 2016
2
Joined
Nov 10, 2016
Messages
2
I am fairly new to electronics. What exactly do you mean by turn the motor on when the output is low? I guess I assumed I would need to run the motor by the output of the 555. Would the frequency be adjustable by a potentiometer?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
If you go to this page you'll notice that for a conventional 555 circuit the time the output spends low is less than the time it spends high.

You need to calculate values so that your low time is about 0.1 seconds and the high time is in some suitable range. Yes, you can have a potentiometer to change this. There are numerous 555 calculators on the net which will allow you to calculate the values of the components you require. If you calculate the resistor values for the minimum and maximum time you want between pulses, you can simply use a resistor of the minimum value and a potentiometer equal to the difference between the values.

To switch the motor on while the output is low you connect it between the 555's output and the +ve supply. This assumes the motor runs of a voltage similar to that required for the 555, and that the current demanded by the motor is not too high (100mA would be the max I'd use),

In addition you need a diode across the motor so it doesn't fry the 555. You'll see this in circuits that use a 555 to switch a relay.

If any of this fails to make sense, let me know the min and maximum repetition rate and I'll walk you through the calculations.

Once you've done this, you need to find a suitable vibration motor. You're in the US, so I'd look at places like electronic goldmine, but others who do not reside at your antipode probably have better advice in this area.

here is an example of a vibration motor.
 

AnalogKid

Jun 10, 2015
2,884
Joined
Jun 10, 2015
Messages
2,884
A motor-vibrator is a small motor with an offset weight. Between the mass of the motor armature and the mas of the weight, there are definite speed up and slow down times. At 0.33 s per vibration burst, is there enough time between bursts to make feeling them separately possible?

ak
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
The diode across the motor will stop it quite quickly, Aside from that, I think you need to try it to see how it goes.

I've had devices that pulsate the vibration quite quickly, so it's not beyond the realms of possibility.
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
You might be able to make it smaller, lighter, and more energy efficient by giving a small electrical shock instead of using a vibrator motor. I'm not joking here, I think you could come up with enough to feel it without it being too unpleasant.

You would do that by having the 555 pulse an inductor, essentially what is called a boost converter. You would want to keep the current in the low single digit milliamp region.

Bob
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
An ordinary 555 has plenty of output current to drive a vibration motor but its minimum supply is 4.5V.
A vibration motor uses a current that is too high for a small battery. A small motor with a weight is listed at using 200mA (!) and a tiny "coin" vibration motor uses 100mA.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,878
Joined
Jun 21, 2012
Messages
4,878
I like Bob's electrical stimulus idea, but instead of a single pulse I would try a gated series of higher frequency pulses, perhaps a few thousand hertz gated on for a few milliseconds. Play around with the frequency, gate width, repetition rate and voltage to obtain a mild tingly sensation about three times per second that is not too distracting. The electrodes for stimulation could either be placed on the bottom of the watch case or incorporated into the wrist band. Some experimentation required!
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
Although a pulse frequency of ~3Hz is doable, do you really need it that fast? For example, would a pulse every three or four paces be sufficient?
As for the vibration, perhaps the piezo transducer used in most watches for the beep sound could be simply driven with a single voltage pulse each time to generate a 'click', which would be unlikely to bother other runners and could probably be felt through the watch case.
 
Top