AVR-Chat

>I am trying to modifying a PIC program to get a shift register to work

> properly, toggle the clear pin on the shift register to force all outputs 

> to

> "0" to prevent it from holding the data for too long and burning out an

> expensive solenoid.

> 

> The shift register is a 74HC595 and will occasionally lock an output on 

> for

> a long enough period to destroy a solenoid.

> 

> These solenoids are $350-00 each and they burn out around 40 to 50 a year 

> on

> the system.

> 

> Have tried a PIC group but have not received any replies.

> 

> I normally use AVR's with a C compiler the more that I see of the PIC the

> more I dislike them!

 

Sounds like a problem with a transient on the supply. Something like an AVX 

TransGuard will cure the problem.

 

Leon 

 

These units are in the field on 12 volt battery supply with solar panel
charging system (no mains supply) the 12 volt solenoid's are driven by
VNP5N07 Fully protected power mosfets     (ST Microelectronics devices)
switching one end of the solenoid to V- the other end of the solenoid is
connected the battery V+ .

The 1N4004 protection diodes are across the mosfets "not the solenoids" (no
diodes across the solenoids).

I had not noticed this before but perhaps the internal resistance of the
batteries may be high enough that the ringing of the solenoid coil could be
causing a spike on the supply??? 

Sorry for the HTML!

Thanking You,

Owen.



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