[sdiy] 4042 latch question

[Scott Gravenhorst]

I don't have the 4042 data sheet, but I looked at a few others, the input
voltage for a guaranteed high for a 4001 is 13 volts when powered by 15.  It
looked like most gates obey a rough rule of 80 to 87 percent of Vdd for a
high.  So no, 5 volts won't make a high on a 12v supply system.  The low will
be a corresponding, but reverse margin.  In fact, with a 4069UB, the output
begins to switch at 1/2 ( Vdd - Vss ) which turned out very useful for a
waveshaper I built.  I think you're going to need to amplify that 5 volt
input signal so that it's much closer to 12 volts while maintaining a signal
as close to zero as possible for a low.


Peter Grenader <petergrenader at mksound.com> wrote:
>
>aaaAAAAAAAAAAAHHHHHH!!
>
>sorry...had to get that out of the way.
>
>OK, a 4042 latch (told you the easy stuff always gets me).
>
>if it's running off of +12, is there any reason the latches will not respond
>to an input where the high state of the D inputs only goes to 5 volts?
>
>If this is the case, then I will have to boost input signal with a tranny of
>something because the device that's generating them cannot go higher than 5.
>
>the problem i'm having is I've got a latch set up, it's polairity is set
>low, the clock input is happening correctly, the d states are doing there
>thing, and all of the outputs are held at low. So, it's not latching at all
>as it should be latching the high or low states at the inputs when it sees
>the strobe.
>
>So the only possible explanation I can think of is the 4042 needs a higher
>high true state than 5 volts to do it's thing.
>
>Honestly, this is a bit of the stretch, but it's the ony thing that's coming
>to mind.
>
>any info/epxerience anyone has with this, i'd be very interested.
>
>thanks,
>
>Peter
>
>

=========================================================  
- What good are laws that only lawyers understand?
- Government: The other religion.
- The media's credibility should always be questioned.
- Thankfully, insects are rather small.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.GTE.NET/res0658s/FatMan/
-- NonFatMan: home1.GTE.NET/res0658s/electronics/