On Fri, 11 Mar 2005 17:52:58 GMT, "Peter Barbella"
wrote:

Hello Gang,

I've got a crystal (7.155 mhz) that I need to use at half frequency. I
decided to pump it into a flip flop, but I'm having an awful time using
2n3904 transistors. The triggering seems to be a very challenging design
issue.

Anybody have any thoughts, (or other ideas for halving frequency)?


Lack of info. What kind of OSC? What kind of FF? Is there an
amp/buffer between the OSC and FF?

Generally this is usually a non problem as at 7mhz most flops are easy
to drive. Typical line up I use for this is a 2n3904 osc (any type),
a capactor coupled 2n3904 common emitter amp with a 1k collector load
and about 100 to 300K resistor between the collector and base to bias
it and couple that into the clock input of a 74LS74/74HC74 wired as
/2 or other config as needed. I also try to bias the flops clock
input to about half the VCC for better results. I've never had this
fail and it works fine to about 30-50mhz depending on FF used.


Allison
KB1GMX