Hi Michael,
I’m sorry to disappoint you but I’m not “Old fellow from Darmstadt and Birmingham”

I’m a not that old guy from Sweden……. ;-)

I really would appreciate if you could help me on this one, I’ve been banging my head against the wall for some time now ……..
You have understood my circuit exactly!!
I’m using port 0.4 with an extra external pullup (10k) on the base of the BC547 and feeding the BTS441 (also tried BTS650P without an luck) with a 4,7k pullup on C of the BC547, the E goes to ground and I have placed a 0,1uF cer cap from the B to ground with some luck, the interference was lowered but still exist.

I have understood my self that maybe I should place a ferrite in series with my MCU port to filter the spikes. But is this enough? What should I do more? In your text you have a cap between the MCU and the highside switch but how should I connect it and what values and so on.
I’m really not that experienced with this kind of problems, I work as a computer technician so if you ask me why your Novell server don’t mount the disks I can probably tell you why……8-)

I was thinking of placing an optocoupler in-between the MCU and my high-side switch but left it out after my first testing that were successful without the optocoupler. I also think that an opto is useless if you get heavy interference so I haven’t tried it, yet…….

If you need to know anything else you can mail me on roger(at)handmade.nu
Of course replace the (at) for a @

Thanks in advance,
/Roger Johansson