Hi friends: I got a serious problem with 74LS123. 74LS123 has been configured as following: 1CLR-----VCC 1A-------GND 1CEXT----100PF( one pin is conected to GND ) 1REXT----120K 1B-------INPUT 1Q-------OUPUT Input keeps changing from 1V to 3.5V repeatedly. Why this chip can not be triggered? Beg for you help....
Hi friends: I got a serious problem with 74LS123. 74LS123 has been configured as following: 1CLR-----VCC 1A-------GND 1CEXT----100PF( one pin is conected to GND ) 1REXT----120K 1B-------INPUT 1Q-------OUPUT Input keeps changing from 1V to 3.5V repeatedly ( 25HZ ). Why this chip can not be triggered? Beg for you help....
A VERY personal opinion I call these devices one shot in the foot. I will, if needed, use 5 chips to avoid using a one shot in the foot. The one shot in the foot chips are the most noise sensitive chips you can find. The mixture of analog and digital circuitry makes for a device that acts different from all other chips of the same family. My opinion Erik
Your circuit description does not line up with the data sheet I have for the 74ls123 - The capacitor is connected between pins 14 and 15, the resistor between pin 16 and VCC (pin 16). Try this configuration and it might have a better chance of working. How do you mean the input is changing from 1v to 3.5v?? Why are you using a 74ls123 to generate a 100mS pulse? If you're using a micro, it is normally more than capable for generating pulses. Methinks a good read of the datasheet is in order. How does this hardware question relate to Keil's C compiler??? I suggest using a different forum.
Thank you for your generous helps... The input to pin 4 is a slowly rising since wave, what I want to do is to use 74LS123 as a interface between analogy input and MCU for producing impluse.
Sounds like you need a Schmitt Trigger, rather than a monostable? Anyhow, what has any of this got to do with Keil software tools...?
so sorry friends... I am using keil c51 to development my project and here is the only place which can appear in my mind right now... Thank you and have a good weekend...