Here is a very low power, sharp edges transistors schmitt trigger I designed because i have no IC handy. Though I would share this to anyone that interested. This has been built and tested

 

Seems to work well, but it's a lot of parts just to avoid using one comparator IC.

 

The classic two-transistor circuit is also very effective.

 

The classic two-transistor circuit is also very effective.

That classic circuit really does not have a Low and High Threshold, noisy signal could cause lots of problem.

 

That classic circuit really does not have a Low and High Threshold, noisy signal could cause lots of problem.

Not so - the thresholds are set by the ratio of R2:R3.

 

Seems to work well, but it's a lot of parts just to avoid using one comparator IC.

1Meg reference voltage divider vs 10k for an IC like the LM393 is the trade off though

 

1Meg reference voltage divider vs 10k for an IC like the LM393 is the trade off though

No-one else mentioned the LM393. It could be a TLC3702, which has 5pA input bias currents and push-pull outputs so it doesn't need a pull-up.