How exact must the duplicate be? Form, Fit or Function? Or just simlilar.
5mm White LEDs have a forward forvate of 2.8V at low current and the internalm series resistance varies with current but is approx 12-24 Ohms at typ. Rating of 20mA
Thus the forward voltage increases with current caused a variation in range in devices for the typical device, which varies but has a Vf of 3.2 @20mA. This fact results of the rise in Vf always rated at 20mA for this type.
Thus when calculating the current for a battery which drops voltage during life discharge, you would use the minimum Vf + Rs or internal "effective series resistance" (ESR) which rises for dropping current, but we can use a fixed value for,determining how much extra R is required for a simple current limiter.
Thus since 3AA cells works well for the 3V white LED, we should use this.
The 9V cell composed of 6 smaller 1.5V cells, or twice the voltage, so if that was selected you could only choose 2LEDs in series with two series strings in parallel. Being a smaller battery, it will have a somewhat smaller capacity than 3AA's and a shorter LED run time, with 2x20mA for 4 LED's@9V than 3AA cells @4.5V supplying 4x20mA.
There are many simple latches.
1. a
counter using the least significant bit or last 2 bits, 00,01,10,11, repeating.
2. An RS flip flop(FF) , a D FF,
3.. A pair of inverting gates to make an RS flip flop.
Let's Consider the 3rd.
But how much extra current can we expect from a Gate?
Depends of the Logic family and internal,resistance.
How do you estimate the internal resistance?
From the data-sheet for Vol/I for selected Vcc for V output Low and (Vcc-Voh)/I for output high.
View attachment 110281
View attachment 110280
Can you calculate the ESR of the 'LVC2G02?
I get a diff. value for High and low.
For Vol , ESR=17 Ohms and for Voh, ESR=22.
But these are more than the 5mm LED, but remembering both values will be useful in choosing serial or parallel strings of LEDs and deciding if you want to drive from the low side or high side.
It doesn't matter much in these parts, does in others. 'LVC2G series are pretty low in the whole CMOS family.
Choosing the current 20mA, we can get away with LEDs from the same batch in parallel wIth either driving two with 1 resistor and the other two LEDs with another 1 series resistor.
Thus for fresh battery voltages, 4x1.65=6.6V
We get using the the high side, Voh ESR=22 and two LEDs in parallel, Vf ESR=16 Ohms average /2 = 8 Ohms +- 50% (12-24) . You can verify with your LED choice if different but this is close enough.
Thus using the White LED threshold Vth of 2.8V, ( take my word for now) we calc as follows;
What happens if we drive the 4 LEDs direct off the NOR Gate?
At nominal Vbat= 4.5V, Vth=2.8V and the high side 22 ESR , we expect the current would be ;
(Vcc max - Vth)/{ESR total} = (6.6-2.8)/{22+8}= 127mA , which woud exceed the chip 50mA max for Vo. This neglects that batteries also have ESR and could be considered, which may be ~1 ohm per fresh battery.
For Vbat nom , (4.5-2.8)/30=90mA
For Vbat dead , (3-2.8)/30=6.7mA or 1.5mA per LED and very dim.
But,we need to limit the NOR gate current to 50mA for reliability reasons and thermal effects.
SO you have a choice to,add,a simple MOSFET driver or use a Quad NOR gate and share the load.
CAPS are not needed wiche the RS FF is not glitch sensitive as repeated sets do not alter the output.
The original schematic shows two single,complementary LED's but only asked for,.4x with On Off control.