[sdiy] gates and clock inputs to a microprocessor

[Chris Muir]

I don't know the LM338, was this a typo for 339?.

One nice thing about the LM339 is that you can power it on +15, but  
have the pullup resistor on the output going to +5 for level shifting.  
You probably will want to add an R for hysteresis to help ensure clean  
transitions. I bet you don't need the Schmitt trigger with the right  
hysteresis R.

- C

On Oct 25, 2009, at 1:09 PM, Danjel van Tijn wrote:

> Hi Chris,
>
> I was thinking about LM338 comparator with threshold set to 2V... this
> way 5V pulses/gates from a midi2cv converter will work but also the
> larger voltages (up to 12V since I am on a euro system) would also
> trigger. The output would be always be a 0/12V pulse which I could
> then divide with resistors or use a opamp with attenuation (to provide
> further buffering).
>
> On Ray Wilsons site he even put a schmitt trigger after the comparator
> (I guess to clean up even more?)
>
> Also I think for my other question about inverse logic at pins it
> looks like on other circuits they are using pull down resistors
> instead of pullups.
>
> cheers,
> Danjel
>
>
>
>
>
> On Sun, Oct 25, 2009 at 12:57 PM, Chris Muir <cbm at well.com> wrote:
>>
>> I went with the conservative approach on a recent module:
>> - comparator on input (339)
>> - voltage follower with gain on output. I needed 10 V gates  
>> (optionally 15
>> V), you could get away with just a voltage follower if you only  
>> need 5 V
>> gates.
>>
>> - C
>>
>> On Oct 25, 2009, at 11:36 AM, Danjel van Tijn wrote:
>>
>>> I am working on module where I have a microprocessor receive gate/ 
>>> trig
>>> inputs for clock and reset controls.
>>>
>>> what do I need in terms of analog circuits to condition those  
>>> inputs?
>>> e.g.
>>> -for input over voltage protection would I use a resistor plus 5V  
>>> zener?
>>> -comparator to allow low voltage signals trigger?
>>> -series diode to protect from negative voltage?
>>>
>>> Also the uP will be outputting gate signals. Should these be  
>>> buffered
>>> or can I just drive straight from the output pins?  (it is an
>>> atmega168)
>>>
>>> Also if the input pins of the microprocess are using pullups, how
>>> would I have an incoming pulse trigger on rising edge? would I  
>>> need to
>>> put it through an inverter?
>>>
>>> I am sure all this stuff has been covered and well documented in
>>> schematics. I am going to head over to MFOS to get some ideas but
>>> thought it would be good to check some other resources.
>>>
>>>
>>> cheers,
>>> Danjel
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>
>> Chris Muir
>> cbm at well.com
>> http://www.xfade.com
>>
>>
>>
>>
>>
>>
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Chris Muir
cbm at well.com	
http://www.xfade.com