time pulse

Posted on Feb 5, 2014

The idea was to show time passing, but instead of a traditional clock face or digits or lights representing binary, to use some kind of tactile feedback. A simple vibrate motor was an obvious choice - used as `force feedback` actuators in video-game console controllers and as indicators in cell phones and pagers, these devices should be well known

time pulse
Click here to download the full size of the above Circuit.

and easy to obtain. Surprisingly, Digikey doesn`t carry anything like what I was looking for. Sparkfun has one for five bucks each. All Electronics has a couple options available now for about as cheap as I`ve seen. Of course paying shipping on a one buck motor is questionable; see if you can find an old cell phone or pager to salvage parts from first. I briefly considered using a 555 timer chip to drive down the cost, but a microcontroller made counting minutes/hours/days a lot easier and I didn`t need to fiddle with much analog stuff. A 555-based circuit would very viable for somebody who only wanted a heartbeat pulse without the extra timing. The crystal frequency is an odd value because I prototyped the project on a development board I had left over from a project that was doing a lot of serial communication at 9600bps: 9600 * 1024 = 9, 830, 400, or 9. 8304 million. I had to fiddle with the fuses on the microcontroller to get it to use the crystal - unfortunately I don`t recall the exact settings. The diode in parallel with the motor is there to catch back-EMF. The motor coil acts as an inductor and I do this trick with much larger motors - figured it couldn`t hurt here. Similar idea with the 100uF capacitor on the power nets - that`ll smooth out any noise from the motor and will provide quick power for the motor. The `SELECT` jumper is there because I was originally planning on putting an LED on the board as well and...

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