Protecting Microcontrollers (was Re:[sdiy] converting a 10v p to p to a 0-5 volt signal)

[Tom Wiltshire]

I've also used the rail limit of op-amps as a solution:

http://www.electricdruid.com/PICCVMixer.png

This has one mixer op-amp, which can't produce an output larger than  
+/-15V whatever it does (lightning strikes and ESD spikes excluded, I  
suppose).
This is followed by a precision half-wave rectifier which deals with  
the -ve voltage, and the gain resistors are set for 1/3rd gain, so  
the +15V in becomes +5V out.

I don't know whether I think this is the best solution or not. Let's  
just say that it's not a problem I've stopped working on.

T.


On 20 May 2009, at 19:16, Jason Proctor wrote:

> my amateurish solution was to power the opamps suitably. the  
> scaling opamp is powered from +/-5v. i put trimmers in appropriate  
> places and tested it with input voltages from +15 to -15. seemed to  
> work ok.
>
> although i did forget about the opamp output DC offset Ray includes  
> in his scale/bias page.
>
> (i've not blown the micro yet!)
>
>
>> 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
>>>  >
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