Using Ne556 dual timer as a bistable multivibrator

Submitted by Dikraji on Thu, 04/13/2023 - 06:17

Hi Since i require two separate Bistable timers that can be set and reset independantly i am using the Ne556 timer. 


I have connected the pins in the following manner.

Pin1 or pin 13- Disch pin:- Not connected  ( floating)

Pin 2 or pin 12 - Thresh :- connected to Ground directly

Pin 3 or pin 11 :- Control :-  connected to ground via 10nF capacitor

Pin 4 or pin 10 :- Reset :- Connected to VCC via a 1.8 Kilo ohm resistor. 

pin 5 or pin 9 :- output :- connected to optocoupler that is used to turn on a relay. 

Pin 6 or pin 8 :- Trigger:- Connected to VCC via a 1.8 Kilo ohm resistor.

Pin 7 :- Ground:- Connected to ground pin.  

Pin 14:- VCC:- Connected to +12V supply 


That is i have connected each of the timers independantly to function as a bistable multivibrator. Now when i trigger and reset the individual timers they set and reset without any issue.  I.e if i make pin 6 low then pin 5 goes high and if i make pin 4 low  pin 5 goes low. Simillarly with the second timer pin 9 goes high when pin 8 is low and is reset when pin 10 is low. Now the problem i am facing is that i cannot make both pin 5 and 9 high simultaneously. If i make pin 5 high first by making pin 6 low then the moment in make pin 8 low pin 9 goes high and pin 5 goes low. 

Can anyone tell me why this is and if i can solve this so that i can have both Pin 5 and 9 high simultaneously. 

Please note that to make pins 4,6,8 and 10 low i am using a push button .Hence they are low only for a few milli sec. as i press and release the push button.

Thank you