| ??? 02/02/06 14:10 Read: times |
#108974 - Need not to work unreliably Responding to: ???'s previous message |
Erik said:
The monostable is about the bitchiest circuit there is. If someone turns on a light switch in timbuktu it might fire. I do everything I can to avoid using one shots 555/221? or whatever.
A counter and a decoder will perform stable, predicatble operation. With small uCs available for less than $1, why not make a stable circuit. Hmm, monoshots and oscillators are equally susceptible against noise on the trigger line. But there's a simple cure: Shielding and filtering. Maybe you have suffered from miscontructions, where shielding and filtering was omitted? Especially engineers doing in digital (I don't mean you, please) tend to handle monoflops not adequately. This is just a problem with 74221: This chip alone is perfect refering to stability and phase noise, but on a board not bypassed properly, on a noisy ground and without proper individual supply voltage filtering all the great performance is lost. Monoflops I use, get always an RC-filter in the supply line. Additonally, I use monoflops which don't produce much noise by themselves, means I prefer the CMOS-555 instead of bipolar 555 for instance. Kai |
