Electronics HDD activity dependant "555 timer"

I'm looking to build the led chaser that's features on Metku here However I'm not quite satisfied with the way it works currently. What I'd like to do is to have a 555 act as a times (as on Metku) but have the 555's speed vary depending on HDD activity. So the more activity, the more pulses, the faster the chaser. Ideally I'd like to make it so that it's chasing even when there's no activity, if possible. As usual, many thanks in advance.

 

You're probably looking at finding a way to modify the control voltage pin of a 555...

 

My knowledge of the 555 is rather nonexistent but if that's what controls its oscillation frequency, then yes.

 

Well, after spending most of the afternoon reading about the 555, I've managed to find that pin 5 allows one to change the frequence according to voltage, problem is it works in reverse to my needs, ie. higher control voltage, slower pulses.
Then there's of course also the problem of converting HDD pulses to a variable voltage. But this can be done with an LM4558N as used on macro's HDD Activity Meter. Still I'd need to adjust the output voltage of the 4558 to be in the range of around 1.7 - 5V. Any ideas anyone?

 

100+ views and not even a nudge in the right direction

 

well as much as id love to help you

 

hi!
first post here...

@on topic:
Have you tried any DAC's?
Guess not.
May-be you could wire a resistor(~10k) and a capacitor(~47uF) in series with the output(activity led) and then send it to a LM3914 based level meter?

should work, but not that sure.
ddes3

ps! really cool smilies!

 

I see your problem. The problem is that the HD led signal has a higher frequency than the 555. Let's say the 555's output has turned HIGH and the hard drive accesses a few times before the 555's output has time to turn LOW. If you look at the 4017's datasheet, a falling edge on pin 13 while pin 14 (555 output) is HIGH increases the counter value. In order to get the effect you want, you'll have to add a latch between the 555 and the 4017. Give me a little time and I'll cook up a diagram for you.

Here you go: http://pages.videotron.com/zwox/pictures/555mod.png

You can also use a 7475 instead of the 7477 but the pinout might be different.

 

Could you try a 555 in astable mode, with an opto-isolator's resistor across one of the timing resistors? (The input for the opto isolator being fed off the HDD activity light)

 

After further reflexion, it might also work well enough if you simply connect the opto to the 555's reset pin like so:
http://pages.videotron.com/zwox/pictures/555mod2.png

 

Thank you very much Zwox, I shall give that second circuit a try, looks promising to me.