[sdiy] best way to convert bipolar to Cmos compatible square/gate?

[nicolas]

Yes, there are two separate issues with analogue -> cmos.
 - you need to clean up the signal with a comparator or schmitt trigger.
 - you need to get the voltage levels in the right range.
These can happen in either order and often people seem to adapt their approach depending on what spare gates, op-amps, etc they have already have available on the board.

But I think the best approach which is the most robust is this:

Use a comparator with an open collector output with separate output ground (eg LM311 or LM319).  Power this from your +/-12 or 15V analogue rails and set the comparator level at 0V or whatever is appropriate.  Use a large +ve feedback resistor to get just a little bit of hysterisis.  Tie the output ground to your digital ground and pullup the comparator output to your digital +3.3 or 5V rail and you will get reliable results every time.

Regards,
Nicolas


----- Original Message -----
From: Tom Wiltshire <tom at electricdruid.net>
To: dan snazelle <subjectivity at hotmail.com>
Cc: *SYNTH DIY <synth-diy at dropmix.xs4all.nl>
Sent: Friday, 21 September 2012 10:10 AM
Subject: Re: [sdiy] best way to convert bipolar to Cmos compatible square/gate?

Can't you find some CMOS gate with a schmitt trigger input that could act as your comparator? Then you'd get the output level you're after. The gate could be anything - 4093 NAND with both inputs wired together?

HTH,
Tom


On 20 Sep 2012, at 22:47, dan snazelle wrote:

> I have been trying all day to find a way to do this without too many parts.
> 
> gone through the cmos cookbook, still no luck.
> 
> 
> basically I am trying to get square pulses from a bipolar waveform.
> 
> my first thought was, Oh, just feed it into a comparator with a threshold pot.
> but that was putting out a square that went from -12v to +12v
> 
> so then i thought, ok I will use one opamp to change the gain, and one opamp to offset it.
> 
> 
> but that made me think.....there must be a better way.
> 
> 
> 
> maybe diodes to a 5v supply?
> 
> or is there a CMOS compatible comparator that reads a bipolar input and puts out cmos compatible pulses?
> 
> 
> 
> 
> THANKS FOR ANY HELP
> 
> 
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy