[sdiy] converting a 10v p to p to a 0-5 volt signal

[Tom Wiltshire]

Do these techniques work on inputs being fed to an analogue-to- 
digital convertor?

Adam didn't mention it, but he's thinking of the ADC inputs on these  
microcontrollers principally. Protecting logic inputs is pretty easy.
For the ADC inputs (CV inputs into the microcontroller) you want to  
be able to mix in external CVs and so forth, and you have no idea  
what might get stuck in the socket. So any solution has to protect  
the micro, but also can't affect the operation of the ADC. Current  
limiting resistors will increase the time for the ADC to sample the  
voltage, I'd have thought. But perhaps not enough to matter - Does  
anyone have any practical experience trying this resistor+diodes  
technique on microcontroller ADC inputs?

T.


On 20 May 2009, at 21:37, Jerry Gray-Eskue wrote:

>
> <<such as the lower limit
> actually being one diode-voltage-drop below zero rather than zero.>>
>
> A good protection technique uses a current limit resistor followed  
> by two
> diodes one the + voltage the other to the - voltage Followed by a  
> Second
> current limit resistor. The voltage at the Diodes can run from ~ .6  
> volts
> above and below the power rails but the second resistor limits the  
> current
> so that the on chip input protection can clamp the .6 volts at very  
> low
> current without being damaged.
>
>
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Adam  
> Schabtach
> Sent: Wednesday, May 20, 2009 12:57 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] converting a 10v p to p to a 0-5 volt signal
>
>
> Aside from range scaling, I'm still looking for a good protection  
> circuit
> for microcontroller inputs. I want hard clipping at 0V and 5V to  
> protect the
> micro. I've seen various solutions described on this list, but when  
> I put
> them into SPICE I have always found some flaw, such as the lower limit
> actually being one diode-voltage-drop below zero rather than zero.  
> I'd be
> very happy if I could find some nice solution to this problem so  
> that my
> micro-based modules can protect themselves rather than having to  
> depend upon
> my poor memory to avoid being subjected to unacceptable voltage  
> ranges. :-)
>
> Or, putting it another way: converting 10Vp-p to 0-5V with op-amps  
> is a fine
> solution, but as soon as you add two 10Vp-p signals together (e.g.  
> mixing
> two LFOs) the input range can easily exceed 10Vp-p and hence the  
> output
> range will also exceed 0-5V.
>
> --Adam
>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
>> Jason Proctor
>> Sent: Tuesday, May 19, 2009 6:50 PM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] converting a 10v p to p to a 0-5 volt signal
>>
>> i did exactly this for my Arduino module. it bidirectionally
>> interfaces a +/-5v signal to the micro's 0-5v range.
>>
>> turned out to be pretty easy - on the way in, chop the signal
>> in half, and bias with +2.5v. then reinvert. on the way out,
>> do the opposite. 1 dual opamp each way.
>>
>> lmk if you want the details.
>>
>> (i should also thank Tom Wiltshire here for his help getting
>> me off the ground with this stuff.)
>>
>>
>>> tonight i was looking at my scope
>>>
>>> Checking the input into a circuit that was only able to take
>> 0-5 volts
>>>
>>> Sure enough, the signal was between 0 and 5 but the sawtooth
>> was clipped.
>>>
>>> So i am looking for a input block that can take either
>>> 5vp to p or 10v p to p (or any synth signal)
>>> and spit it out as a 0-5 signal without squaring the top.
>>>
>>>
>>> anyone know of a good circuit for this?
>>>
>>> thanks
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
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