POV HDD Clock Sketch Help

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi Guys,

So, I've gone through the instructable for building a POV HDD Clock, and I'm having a problem I hope one of you can help me with.

Here is a link to the Instructable. Maybe the author of this instructable is on this forum?

http://www.instructables.com/id/Hard_Drive_Persistence_of_Vision_HDPOV/

If you look through the instructable, the code can be found at the end.

The only thing I did differently from the author was I used an optical interrupt package rather than building one out of discreet components like the one detailed in his instructable. Here is the interrupt I used:

I looked at the output of the optical interrupt on my o'scope, and the output is reading the speed of the Hard drive correctly, and is outputting 5V on every revolution. I can upload a couple of screenshots of the scope readings when I get home if you guys think it will help.

I have also verified that the LED strip is working by putting 12V across each of the signal lines and the common line and it works.

I suspect that the sketch provided was taylored specifically for the discreet component interrupt switch solution that the author designed, and that the sketch needs to be changed in some way to understand the optical interrupt package I used. I have looked at the sketch so many times that I'm running around in circles in my head and can't seem to isolate what might need to be changed to get the system to work.

Specifically, the problem I'm having is that the LED strip will not light up when it is placed in the system, but it will light up when I power it up directly with 12V.

Any help anyone can offer would be greatly appreciated. I can provide more details too when I get home and look over my notes.

2

There is one thing that might be a bit of a hitch... but it's an idea... so I could be wrong. Logic inversion...

Instructable used a transistor with a PULL-UP so it goes LOW when LIGHT HITS IT though the gap and HIGH when the disc is blocking light.

The Sensor you have says:

Schmitt trigger and an NPN output transistor with 10 k (nominal) pull-up resistor. The buffer logic provides a high output when the optical path is clear, and a low output when the path is blocked.

So... in addition to having slight hysteresis from the use of a schmitt trigger in the design... the trigger inverts the logic so it becomes the opposite logic when it reaches the NPN... so you need to do a an extra logic "invert" to UNDO what the added trigger did. That way you get the same results... You can do it in code... luckily.

3

Thanks for the insight. I will try to undo the inversion in the code.

The only thing is...Wouldn't the inversion still allow the LEDs to light, just not correctly?

In any case, I will try to find the inversion point and correct it in the code. If I can't find it, I'll build an inverting op-amp and try that.