frequency divider

[ngogketrao]

  hi!
 
  can you give me a hint on how to make the display switch more periodically for the first circuit?

  concerning the second,it is supposed to be a frequency divider circuit but when i connect the oscilloscope to check the frequencies, i don't get the results expected,it should divide the initial frequence by 16.
 
   thank you!

[Lodin]

hello ngogketrao ,

1 : the 7490 is an asynchron counter. Your circuit is right, but the simulation shows the "steps betweeen" the counting steps.

2 : 1mOhm or 1MOhm for R1 ? I dont know what you are doing with J1 & J2, but they use the same key (Space).

regards, Lodin

[lacy]

I am responding to the first circuit in you posted about the counter jitter. This can't be totally eliminated but can be diminished some. What you have to do is to is goto SIMULATE>INTERACTIVE SIMULATION SETTINGS>ANAYSIS OPTION. Click the circle next to USE CUSTOM SETTINGS Then click CUSTOMIZE.  In this page click TRANSIENT Tab.  Look down to the last option called INTEGRATION METHOD (METHOD). Click the little white box next to this to put a check mark into it. Now in the white box beside this where it now says TRAPEZOIDAL you need to use the little down arrow to see more options. Once these option appear select GEAR. Then click all the O.K. buttons to close all the boxes.

This will smooth it out somewhat, but like I said it won't totally eliminate this. At least the diplay will look more like it should when it is counting.

I hope this helps some.

I am looking at you second circuit, but I am not really clear on what your trying to accomplish with it. Maybe you could give me a little more detail on what your expecting it to do. What is confusing me is the switches. J1 doesn't seem to affect the circut in any manner. J2, on the other hand, will enable or disable the output. Also, what frequency are you looking for from the 555 Timer? If you could just address this then maybe I came come up with a solution for that one also.

[kittmaster]

wrong thread......sorry

Message Edited by kittmaster on 11-24-2007 08:59 PM

[ngogketrao]

In  the second circuit,as you mentioned the switch J1 seems to have no effect on the circuit while it should.

       the switch J2 is supposed to select the output either from the single-step circuit or from the continuous-clock circuit output and switch it through to the frequency divider circuit ,this signal will serve as input to the frequency divider circuit where it will be divided by 2 at each stage( by 16 for all the four stages).

      the switch J1 should generate a LOW or HIGH for the single-step circuit. 

     I attached a slightly modified version of the circuit with comments and more specifications. I hope it is enough to understand the behaviour of the circuit.
    thank you

[lacy]

Your circuit is working as you want it to with the exception of the timer. You have R1's value listed as 1mOhm. This is too low a value for R1. The minimum value of R1 can be is 1KOhm. You are going to have to refigure your components to the timer otherwise it will not work.

Keep this in mind when designing .with the 555. A rule of thumb is that if the resistors are less than 1K or greater than 10Mohm then you need to adjust the capacitor value either higher or lower to get these resistors in that range. This is from my studies and reference material on the 555 timer and is just a general guideline to follow and they vary depending on which reference material you read, but the datasheet urges against any values less than 1K or greater than 10M.

[lacy]

I forgot to mention one other thing. You have J1 and J2 assigned to the same key. Unless you are using the mouse pointer to actuate the switch then these need to be on separate keys. You can double click the component and assign a different key for each one. This is just one of those helpful suggestions that you can use if you want.