hi, today i tried to construct the above circuit. I wanted a simple latch circuit to provide a digital input to a second board. I couldn't get it to work ive got a 4001 quad nor gate, what can i do next?

do i need an alternative circuit design? i am operating at 6v

thanks for reading...

 

You need to make some changes to the inputs. Use 20K resistors, and arrange then as pullups - they connect to the +6 rail and to both inputs.

Use a single switch, but SPDT (single pole double pole) instead of SP NO. The idea is to have one input pulled to ground through the switch, while the other input is pulled up with a resistor.

 

Your circuit should work fine the way you show it. When the input is high then the output of a NOR gate is low. The switches should be momentary.

But the ordinary Cmos gates have a very low output current when the supply is only 6V. The LEDs will be dim and might prevent the output voltage from being a valid logic high.
Use the other two gates in the package or two transistors to buffer the outputs of the gates from the LEDs.

 

As has been said, CMOS doesn't drive even light loads well. Use this to buffer the LEDs and the gates...

 

thanks for everyones replys

i wont be needing the led's i just need a single output to connect to my digital input on my i/o board

would i need to use a buffer or should i increase the resistors to 20k, i will try later this morning and post the results. Essentially i just need the circuit to latch. I am using a reed switch (normally closed) for the alarm, and a microswitch (can be normally open or closed) for the reset

thanks again!

 

Like Audioguru said, the 10k resistors are fine.

Tell us more about the reed switch being normally closed.
Is it opened momentarily when the alarm sounds?
Or is it held open when the alarm sounds?
Or is it held open until the alarm sounds, then closed momentarily?
Or is it held open until the alarm sounds, then closed until the alarm is turned off?

It's going to take some different wiring to hook it up, depending upon how the reed switch is used.

You'll need to use the same voltage level for your board as the I/O board requires.

 

Like Audioguru said, the 10k resistors are fine.

Tell us more about the reed switch being normally closed.
Is it opened momentarily when the alarm sounds?
Or is it held open when the alarm sounds?
Or is it held open until the alarm sounds, then closed momentarily?
Or is it held open until the alarm sounds, then closed until the alarm is turned off?

It's going to take some different wiring to hook it up, depending upon how the reed switch is used.

You'll need to use the same voltage level for your board as the I/O board requires.

The read switch is normally closed and breaks (goes normally open) monentarily on alarm. The reset switch is a micro siwtch with normally open and closed contact and can be arranged to suit.

Both the latch and third party interface operate at 6v