Pages: [1]   Go Down
Author Topic: Auto Reset of JK FF  (Read 980 times)
0 Members and 1 Guest are viewing this topic.
0
Offline Offline
Full Member
***
Karma: 0
Posts: 235
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Is it possible for doing a Auto reset of JK FF. like putting JK FF to output 0 wen I switch on the power supply and maintaining it till next clock pulse comes(ie) without me manually clearing it ). I am using a 7473 JK FF IC. It has a CLR pin. which is active low.
Hoping for fast reply... smiley
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17301
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

It's been several decades, but I recall seeing and using "auto-reset" on flip flops when desired. The method used was a series resistor and capacitor. The resistor was wired to Vcc > cap >ground. The junction of the cap and resistor wired to the direct reset pin on the FF. The time constant used was such that the FF would be held in reset mode until the cap's voltage raised to higher then a legal TTL high state.

Lefty
Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 634
Posts: 34519
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Depending on the type of JK FF you can have preset and clear inputs. You can use these along with an R & C to set the FF state to what you want.
Logged

0
Offline Offline
Full Member
***
Karma: 0
Posts: 235
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanks lefty  smiley
It worked played around with time constant and made it work. But actually how should i design the time const? currently i am using 47k and 1uF cap. It is working though.
I gave it as Vcc(5V) -> resistor -> cap -> gnd. and voltage across cap was given to reset pin.
« Last Edit: June 02, 2010, 11:25:47 pm by dev_000 » Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17301
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
It is working though.

Well thats what counts (a little flip-flop joke).  smiley-wink

Actually the time constant really depends on the whole circuit application requirements. If you need it just to ensure starting in a know state then what you have is fine. If you needed to slow it down for other circuit considerations then maybe 10ufd might be required, which was a common value used if I recall correctly.

Lefty
Logged

0
Offline Offline
Full Member
***
Karma: 0
Posts: 235
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanx guys  smiley
Logged

Pages: [1]   Go Up
Jump to: