I am looking for a simple positive logic RS latch that runs around 3 volts since it will interface with an ISD 1820 voice module. It seems like most IC’s run from 5 to 18 volts and I don’t want two power sources. Kind of a newbie as far as finding things.

 

The old CD4000 CMOS series logic will operate from a single supply of 3V to over 15V.

 

An SR latch can be made from two inverting gates. 74HC00 and 74HC02 will run from 3V and do the job.
There are lots of 74series families that work down to much lower voltages (1.8V for instance)

 

The 74LVC1G family of parts will work on power supplies from 1.65V to 5.5V

 

One possible advantage of the CD4000 series is that they are relatively slow, so are less sensitive to high frequency noise, if that's a consideration.

 

 

Or (no pun intended) with a single OR gate, this one:



Using a CD4071B, it was quite happy at 2.4V switching one of my Superbright green LED's with a 22k series resistor to ground on the output, and a 10k for RX.

 

If having the two inputs be different logic polarities is ok, a 555 will do this in only 8 pins. And - you get the extra-beefy output stage in case the circuit is driving something that needs more than a few mA.

Here is a 555 version with identical input logic polarities.



http://www.seekic.com/circuit_diagram/555_Circuit/555_TIMER_AS_FLIP_FLOP.html

ak

 

Here is a 555 Set-Reset flipflop with differing input logic polarities.

SW1 and SW2 can be combined into a single SPDT switch, either standard or momentary, with or without a center-off position.

ak

 

I didn't see it written anywhere, but the timers need to be a CMOS type 555 to operate at 3V.

 

An LMC555 is guaranteed to work with a 1.5V supply. It can be a set (trigger input goes low) then a reset ( threshold pin goes high) latch.

 

An LMC555 is guaranteed to work with a 1.5V supply. It can be a set (trigger input goes low) then a reset ( threshold pin goes high) latch.

There are two variations of that. One of them is in post #9.

ak