[sdiy] Staircase Generator: 4 bits but 8 steps?

[Tim Ressel]

Hey Chris,

Um, are you getting 0V at some point as well?  A quick
sanity check would be to put LEDs on the outputs of
the LS93 and clock it slow enough to see the count.

How is the '93 hooked up? Are you clocking pin 14? If
you are clocking pin 1, pin 11 should go to pin 14. If
you tied pin 8 to pin 14, you would get funky output.

What you clocking with? A messy clock could mess
things up. Also it doesn't hurt to put a bypass cap
across that counter.

--TimR


--- xamboldt <xamboldt at earthlink.net> wrote:

> I sent this message yesterday, but so far it hasn't
> shown up on the list -
> apologies if you get it twice...
> 
> 
> Hi Everyone,
> 
> I breadboarded an EFM staircase generator. It uses a
> 74LS93 to generate the
> 4 binary digits, but I'm only hearing 8 steps on the
> staircase. It's a 4-bit
> device, and 4 bits is 16 steps, right? Shouldn't
> there be 16 steps on the
> staircase? From what I understand, the D/A section
> is pretty standard - see
> the asciimatic below:
> 
> 
>          20K
> Bit 3 /\/\/\/\------------to opamp buffer
>               /
>               \10K
>               /
>          20K  \
> Bit 2 /\/\/\/\-
>               /
>               \10K
>               /
>          20K  \
> Bit 1 /\/\/\/\-
>               /
>               \10K
>               /
>          20K  \
> Bit 0 /\/\/\/\-
>               /
>               \20K
>               /
>               \
>               |
>              GND
> 
> 
> At first I thought maybe that Bit 3 wasn't getting
> through, but according to
> my continuity tester, it's hooked up. Yes, pins 12
> and 1 are connected to
> utilize the 74LS93 as a full 4-bit counter.
> 
> Should there only be 8 steps on the staircase even
> though it's a 4-bit
> counter? Or is something not right?
> 
> BTW, I'm getting the following voltages from the
> output:
> .2943
> .622
> .935
> 1.306
> 1.594
> 1.980
> 2.351
> 2.811
> 
> Thanks,
> Chris
> 
> 



	
		
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