Quote:
Originally Posted by goldfinder
If you are relying on the 555 to stay on frequency then you are operating without exact frequencies.
The 555 use capacitors and a resitor to control the frequency. The capacitors change values slightly in different temperatures which results in frequency drift. You need to periodically check the frequency as the tuning will drift all over for the original setting. This is especially true in warmer weather. So if your electronic dowsing is dependent on an accurate stable frequency 555s are NOT the answer. 
I have done hundreds of tests in the field and quit using 555s for and kind of stable frequency generator. I use a PIC microcontroller to generate frequencies and they are extremely stable. 
Goldfinder |
This is the reason that i have Test Points at the 555 output