How do I build a bracelet that vibrates once every n minutes?
See end for possibly suitable vibrator motor new from Digikey.

In 2000/2001 I built something that did essentially this as a "disability aid". A small number were built and put in use 


"RIBBET"        Personal Timer

Repeating Intermittent Beeping/Buzzing Electronic Timer

This had a young person / teenager focus and the name was intended to be 'fun'.
Place it on a table and it matched its "frog" image nicely.  


Swallowing as a means of saliva control is a natural reflex for most people - so much so that the vast majority of people would not realise that they do it - or what would happen if they don't occasionally swallow. Many people with Cerebral Palsy can have a lack of awareness of "drool control" and salivation is a common side effect of cerebral palsy - and a major bar to "normal" social interaction. 
Suitably committed CP sufferers may be able to control salivation if reminded of the need to swallow at regular intervals. 

My device addressed this need by providing a vibrating alert with user variable inter-alert period, vibrate pattern and vibration amplitude. A user programmable  timed reminder with discreet user-notification obviously has many other uses. A tone alert was also an option. In some applications tone only was used.

I used a low pin count PIC processor driving a cellphone vibrator motor and/or a "beeper". The battery was a pack of 3 NiCd (Nimh?) button cells.  Housing was a very small potting box with the unit worn under clothing (usually) as an around the neck pendant.

Basic operation was as simple as user on/off disable with a switch press and vibrate and/or audible signal confirmation BUT functionality was user or care-giver programmable as desired. Interface was 3 x spst push buttons which allowed repeat rate, length of vibrate pulse and number of pulses to be varied. Vibrate amplitude was also  programmable to allow "enthusiasm" of alert and audibility to others to be traded off. At full amplitude, if placed on a table the unit would happily walk across the table under vibration and fall off. The optional beeper used a self oscilating DC powered sounder using a wound electromagnetic element rather than a piezo as these allowed easier compact consistent output at low voltage with good volume.

The program was written in (don't tell Olin) ME Labs compiling BASIC - making the logic easily transferable to other languages or processors.

Assuming the documentation is still available in my records (which it certainly should be) the program is available to anyone interested for free for non commercial use. Even if wiring in another language for another processor family this should allow quicker implementation - but the task is a simple one. See my user page for email address. 



Alerters:

DIY A customer alerter using either electomechanical vibration or piezo actuation should be "easy enough".

Shock:  Minor "electric shock (T.E.N.S. style) may be usable. 

"Tick" In many contexts a very subtle audio cue may be acceptable. eg a short sharp low amplitude "tick" noise (fricatives with no apparent tonal information)(eg click tongue, snap fingers)(but QUIETER) may suffice. Even if audible to others they may well not be able to locate or identify it :-)

Vibrator  

Small electric motor with offset centred "bob weight to cause vibration.

Surplus Surplus but new vibrator motors are available at modest cost. 

New: Digikey sells this NEW vibrator motor ex stock for $4.70/1 in stock.
 Minebea vibrator motor with bob weight
 From 1V at 40 mA, start at 0.5 V,
 5mm X 5mm X 10mm - Too large?





Manual for my Ribbet implementation here  (2001) . 

You can buy recycling settable alarms/timers - usually with a piezo beeper output. These could be easily converted to drive a vibrator motor. 

A microcontroller would be most flexible, but if you wanted to "roll your own" then a dual 555 or CMOS Schmitt inverter or counter solution would be easier if you have no experience of microcontrollers.