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
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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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