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

Dan Snazelle subjectivity at hotmail.com
Wed May 20 23:22:22 CEST 2009



looks good but my first question is whether or not (before i build it)
you have had luck with it working with other voltage ranges? (sure would be nice if this would work for 0-5 or +/- 5 or +/-10)


highly appreciate this!





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----------------------------------------
> From: tom at electricdruid.net
> Subject: Protecting Microcontrollers (was Re:[sdiy] converting a 10v p to p to a 0-5 volt signal)
> Date: Wed, 20 May 2009 22:06:06 +0100
> To: jason at redfish.net
> CC: synth-diy at dropmix.xs4all.nl
>
> 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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