Set/reset discrete flip flop with always the same start state needed.

[neazoi]

Hello, I need a schematic for a discrete (transistors) flip flop with set and reset in the same pin.
The flip flop should always begin in the same state i.e the right hand side to begin always with a set etc.

 

[FvM]

A sequential switching bistable multivirator as shown in this tutorial. https://www.electronics-tutorials.ws/waveforms/bistable.html

Add a capacitor or select asymmetrical resistor values to achieve defined start-up.

 

[neazoi]

A sequential switching bistable multivirator as shown in this tutorial. https://www.electronics-tutorials.ws/waveforms/bistable.html

Add a capacitor or select asymmetrical resistor values to achieve defined start-up.

You mean the 4.7k or the 100k ones? Any proposition for the resistor values?

Also, do you know if the trigget pulse can be a pulse from 5v to zero and back to 5v? Or does it have to be a negative voltage pulse?

 

[BradtheRad]

Here is a toggle input bistable multivibrator.

The input must be a brief positive pulse.

If you want to ensure it will always start up with one output high, you must introduce non-symmetry. This can be done by altering one resistor value (see the one at upper left).

This simulation is from a circuit found at the link below (1/4 of the way down). Redrawn with NPN transistors, and a positive supply.

https://www.navymars.org/national/training/nmo_courses/NMO1/module9/14181_ch3.pdf

 

[neazoi]

Here is a toggle input bistable multivibrator.

The input must be a brief positive pulse.

If you want to ensure it will always start up with one output high, you must introduce non-symmetry. This can be done by altering one resistor value (see the one at upper left).

This simulation is from a circuit found at the link below (1/4 of the way down). Redrawn with NPN transistors, and a positive supply.

https://www.navymars.org/national/training/nmo_courses/NMO1/module9/14181_ch3.pdf

Can I replace the mechanical switch with a NPN (emiter connected to the 10k and collector connected to 5v) so that it's base can be driven electronically from a microcontroller?

 

[BradtheRad]

Can I replace the mechanical switch with a NPN (emiter connected to the 10k and collector connected to 5v) so that it's base can be driven electronically from a microcontroller?

Yes, you can use a transistor in place of the switch. Since it is close to the positive supply, you'll find a PNP works better than an NPN.

 

[neazoi]

Yes, you can use a transistor in place of the switch. Since it is close to the positive supply, you'll find a PNP works better than an NPN.

Ok I will use a 2n2907 for this transistor and two 2n2222 for the multivibrator and let you know.
Thanks