Musicmanager
Well-Known Member
Morning Guys
Firstly, please bear in mind I'm a complete novice taken up a new hobby and trying to get my head round some very confusing stuff. I divide my hobby time between building a project I've already thought through and planned with the help of you guys and thinking through, planning and understanding the next project.
My next 'thinking project' is to do with countdown timers. I built a countdown timer based on a PIC 16F628a which counts down from 5 discreet bases 8, 16, 24, 32 & 40 mins using code provided for me by a Picprojects kit which works very well. I now want to understand how to build a countdown kit with 7 segment LED displays which can be preset to the same bases and will display the countdown. I've got a schematic drawn by one of the members on here which uses a 74LS192 IC up/down controller and I decided the best thing to do first was to understand how that chip does what it does ! I downloaded the datasheet which has a narrative of it's operation and also a graphic circuit diagram of the logic gates contained. I've read the chapters on logic gates in my books 47 times and decided I was now ready to try and understand the chip.
Failure !!!! - the diagram shows some of the logic gates with 6 or 7 inputs !! My books show only two in most cases - so some must go to one input and some to the other ? But there is no indication how this is done so how do I work out what will happen when a high or low + or - arrives at an input ?
Since this is more about me learning than the optimum operation of a digital countdown timer, I'm not interested in changing the schematic to another project, I just simply want to understand how this one works by developing my own analysis skills.
A suggestion of where I'm going wrong would be much appreciated
Thanks
S
Firstly, please bear in mind I'm a complete novice taken up a new hobby and trying to get my head round some very confusing stuff. I divide my hobby time between building a project I've already thought through and planned with the help of you guys and thinking through, planning and understanding the next project.
My next 'thinking project' is to do with countdown timers. I built a countdown timer based on a PIC 16F628a which counts down from 5 discreet bases 8, 16, 24, 32 & 40 mins using code provided for me by a Picprojects kit which works very well. I now want to understand how to build a countdown kit with 7 segment LED displays which can be preset to the same bases and will display the countdown. I've got a schematic drawn by one of the members on here which uses a 74LS192 IC up/down controller and I decided the best thing to do first was to understand how that chip does what it does ! I downloaded the datasheet which has a narrative of it's operation and also a graphic circuit diagram of the logic gates contained. I've read the chapters on logic gates in my books 47 times and decided I was now ready to try and understand the chip.
Failure !!!! - the diagram shows some of the logic gates with 6 or 7 inputs !! My books show only two in most cases - so some must go to one input and some to the other ? But there is no indication how this is done so how do I work out what will happen when a high or low + or - arrives at an input ?
Since this is more about me learning than the optimum operation of a digital countdown timer, I'm not interested in changing the schematic to another project, I just simply want to understand how this one works by developing my own analysis skills.
A suggestion of where I'm going wrong would be much appreciated
Thanks
S