DS1302 giving odd values

Im building a qlocktwo myself as a project, now for that i needed to control 27 leds. I also wanted to be able to change the brightness with an ldr since the clock will be hanging in my room so that when to room goes dark the clock's brightness goes down.

But since you do not have enough pwm pins i did this with 3 daisy chained 74hc595.

What i don't understand is if i set my brigthness all the way than it's working fine. if i bring the brightness only slightly down than my DS1302 suddenly starts giving times like 0:0:0, 38:38:38 or 64:05:64 and eventually the arduino stops running the program. I don't really know why since the RTC has no connection with the pwm port of the 74HC595 IC...

Set the brightness at 255 and everything works fine with no problems at all, anybody knows what's going on?

I understand what you are asking (I think) bit there is not enough information to begin formulating a guess as to what is happening. It is most likely hardware gut that is a guess. If you upload a drawing that would help, the software guys would probably want to see your code. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

Where's your project schematic & code?

Hawkie001:
the RTC has no connection with the pwm port of the 74HC595 IC...

A shift register doesn't have a PWM port. Are you trying to apply PWM its enable port by chance?

Duplicate topic deleted