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

[xamboldt]

Hi Tim,

Thanks for the suggestions - very helpful. It's hooked up like this:

http://www.ele4music.com/pdfs/lfo5a.pdf

The only difference is I'm powering it from a regulated 5V supply, not the
zener. And I've got a diode parallel to the 2k2 resistor in the
differentiator that clocks pin 14 (cathode to pin 14).

Pin 1 is clocked from pin 12 (LSB) like they say to do in the '93 datasheet
(your suggestion of of clocking from pin 14 and connecting 11 to 14 should
work, too).

No bypass cap, yet...

I hooked up some LEDs like you said, and there is something screwy
happening. Pin 12 (bit 0) is always on. Well, not quite always. I have it
normally clocked from a 555 that's also clocking a sequencer. When that is
clocking it, bit 0 is always on.

I then clocked it from the pulse out of an MOTM 300 VCO (about 50% duty
cycle), and when the VCO was reallllly slow, for maybe 1/2 of a clock pulse
at the beginning of the staircase, bit 0 would be off, then it would come on
and stay on for the rest of the sequence. At higher clocking rates, bit 0
would always stay on.

All the other bits appear to be working properly, except they're acting as a
3-bit counter, since bit 0 is staying on.

Seems like it is a clocking issue. Maybe try a different differentiator on
the front end? Any ideas?

-Chris


On 9/6/05 5:44 PM, "Tim Ressel" <madhun2001 at yahoo.com> wrote:

> 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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