P.O.V. toy - direction sensing

[justDIY]

I've built a simple 8-led "POV Toy Wand" using a 12f683 and a shift register ... it displays messages just fine now that I've got the timing worked out.

the problem remains however of direction sensing. when waving the toy back and forth, the words are rendered front and backwards, on top of each other. I'd like to figure out a simple way to 'direction sense' so the processor blanks the display for the return sweep (and possibly in the future reverses the data or something else entirely)

mercury switches would have worked last century, but toxins are a no-no now, so what is left? I remember seeing some sort of 'switch' that had little pads and a steel ball trapped inside it - but that was in a movie I think.

do such switches exist, and if so, what are they called, and more importantly, where can an avg Joe get a few on the cheap?

 

[Torben]

I think most folks use an accelerometer for this. I haven't tried it, but at **broken link removed** there is a list of different types. The second type mentions wand message devices as an application.


Torben

 

[ericgibbs]

hi diy,
You can still get the mercury type 'tilt' switches, but as you say they are potentially toxic.
More user friendly types of 'tilt' switches are available.

In the past I have used a small 'ball bearing' about 4mm dia to make a shake switch switch.

Perhaps something like a light weight miniature microswitch with a small/heavy weight at the end of the operating lever
could be used as direction sense switch.
It would be possible to make your own intertial switch with a small weight and a piece of pcb or phosphor bronze strip???

I have used the type that have a stiff wire operating lever, with a small 'paddle' at the end, so sensitive,
it was used to detect air flow from a fan.

Any help?

 

[justDIY]

Eric,

your weighted switch idea sounds promising ... I'll have a look through my catalog and see if I can find an inexpensive tact switch with a low threshold force (the one i'm using now is 260grams, feels like a lot). put a small fishing weight on the button for the switch, and mount it sideways to the PCB. wand swings fast enough one way, g-force pushes the button in, swing the other way, no push.

Torben,

thanks for the suggestion but an accelerometer or other MEMS type device is way outside the budget for this project. Cheapest I could find was an old Analog Devices XL202 for $8 each.

update, here are some pictures to share:

**broken link removed**

this is the pov toy itself, the circuit board is about 2.25" by 1.1". the wires attached are ICSP for the pic chip. The pic is driving a 74hc595 shift register. The button turns the pic on and off via interrupts and low-power sleep mode. there are pads on the pcb for a low-cost SOT23 hall sensor, in case I wanted to place the gizmo in something rotating (like Ada's spoke-pov project)

**broken link removed**

 

[justDIY]

any other ideas?

 

[ericgibbs]

hi diy,
>>
this is the pov toy itself, the circuit board is about 2.25" by 1.1". the wires attached are ICSP for the pic chip. The pic is driving a 74hc595 shift register. The button turns the pic on and off via interrupts and low-power sleep mode. there are pads on the pcb for a low-cost SOT23 hall sensor, in case I wanted to place the gizmo in something rotating (like Ada's spoke-pov project)

What if, you enclosed a small bar magnet, inside a plastic tube, [the type of bar magnet used with a miniature reed switch], close to the hall sensor, so that when the wand motion is left or right it could be detected.
The magnet would slide to one end of the tube.

If you dont want to fit your hall sensor at this time, can you mount a minature glass reed switch next to the magnet tube.
If you have the space you could have a reed switch at either end of the tube??
Left/right blank off the display reversal and/or power the led's.

 

[Norlin]

dunno if something like this would work https://www.mouser.com/search/ProductDetail.aspx?R=D6B-2(P)virtualkey65300000virtualkey653-D6B-2
Maybe, the movement would be fast enough that the sensor would "feel" like it's being tilted?

You spoke of those plastic boxes with the metal ball inside. I have a few of those at home in clear plastic cases, maybe about 1" cube with a large metal ball inside and some contacts on 3 axis. They're really old and I "inherited" them from a friend of my dad so unfortunately I have no idea where they come from. I'd take a picture for you, but am at work.