A timer question

Hi,

I need help to get a one-shot pulse generator with
both positive and negative trigger input. 555 timer
only takes negative trigger input. 74LS123 can take
either positive or negative but not both.

Thanks a lot for help!

Tom

 

[John Fields]

On 8 Jul 2005 13:57:34 -0700, songtao32@gmail.com wrote:

Hi,

I need help to get a one-shot pulse generator with
both positive and negative trigger input. 555 timer
only takes negative trigger input. 74LS123 can take
either positive or negative but not both.

---
You could wire up one of the one-shots in a '123 to trigger on a
low-going edge, the other to trigger on a high-going edge and then OR
their outputs.

--
John Fields
Professional Circuit Designer