Another tale in the category of stupid mistakes:

I had a design with a walwart power supply followed by 7805 volt regulator to 
use in PIC projects. The regulator has small value caps on each end as 
suggested by 7805 datasheet, enough for transients, but not good for filtering 
AC after rectifier (1 diode, used as polarity reversal protection).  I ordered 
bunch of 9VAC, 1A wallwarts and plugged them into regulator.  

Result: strange behavior of the PIC, cannot program it.  Tried ICD2, Tait-style 
homebrew and ICD-U40 from CCS.  Nothing works.  Then noticed that power 
indicator LED is not too bright and flickers when load is applied to the 
regulator.  Figured there must be something wrong with the regulator.  Hooked 
up a scope and saw nice rectified pulses on the input of the 7805!

Conclusion: It helps to order parts not in a hurry, and read label carefully.  
Next time I ordered 9V<b>DC</b>, 1A wallwart and everything is fine.

So if anybody needs 9VAC,1A wallwarts, let me know.

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist