[sdiy] Re: reset circuit for LFO

[Danjel van Tijn]

someone on another forum suggested using a discrete JFET (maybe an
mpf102?) instead of the switch in order to minimize the on resistance.

In this application case (given short input pulse) could I simply
connect D to the LFO timing cap, S to gnd and G to the jack input?

Do I need any resistors at all?

cheers,
    Danjel



On Mon, Oct 19, 2009 at 12:10 PM, Cynthia Webster
<cynthia.webster at gte.net> wrote:
> Danjel van Tijn wrote:
>>
>> oops not a diode to ground, a diode inline!
>>
>>
>
> Right!
>
>>> Is it as simple as putting a small cap between signal and ground of my
>>> reset jack?
>>>
>
> Yes, play with the values a little maybe the MIDI wants a bigger cap lie
> 100pf ?
>
> Best Wishes!
>
> Cynthia
>>>
>>> Should I also be putting a diode to ground to protect the CMOS chip
>>> from any negative voltage?
>>>
>>> cheers,
>>>  Danjel
>>>
>>>
>>>>
>>>> You might try a "pulse stretcher" circuit essentially adding a small
>>>> something picofarad cap
>>>> to lag the incoming clock a bit... (would be simpler than adding a
>>>> comparator and pulse
>>>> conditioning circuit with debouncing etc?
>>>>
>>>> Best Wishes!
>>>>
>>>>
>>>> Cynthia
>>>>
>>>>
>>>>
>>>> Danjel van Tijn wrote:
>>>>
>>>>>
>>>>> Someone suggested using the circuit that Ken Stone used on the clock
>>>>> input here:
>>>>> http://www.cgs.synth.net/modules/cgs13v2_gated_comparator.html
>>>>>
>>>>> A comparator with a diode like this might help me out.
>>>>>
>>>>>
>>>>>
>>>>> On Mon, Oct 19, 2009 at 8:16 AM, Danjel van Tijn <danjel at gmail.com>
>>>>> wrote:
>>>>>
>>>>>
>>>>>>
>>>>>> A while ago I posted asking for advice on modding a Livewire Vulcan
>>>>>> lfo so that it could be reset.
>>>>>> Amos suggested using a CD4053 switch to control the timing cap being
>>>>>> shorted to ground temporarily to cause a reset.
>>>>>>
>>>>>> As first experiment I had two wires: one to the timing cap and one to
>>>>>> ground. Whenever I connected these together temporarily it
>>>>>> successfully reset the LFO.
>>>>>>
>>>>>> Next step was  wiring up a little board with the switch circuit. The
>>>>>> reset jack was connected to one of the control inputs of the cd4053 so
>>>>>> that a short pulse would temporarily connect the LFO timing cap to
>>>>>> ground.
>>>>>>
>>>>>> So far it kind of works but not well:  If I feed at an LFO squarewave
>>>>>> from a Plan B ELF LFO  it holds the Vulcan in reset while it is high
>>>>>> and then allows it to cycle when it is low. However when I switch to
>>>>>> the alternative narrow pulse square waveform the pulses seem to be too
>>>>>> short to cause a reset.
>>>>>> Also when I connect a midi2cv converter and generate clock pulses or
>>>>>> gate signals they are unable to cause a trigger.
>>>>>>
>>>>>> Right now the 4053 is being powered by the 12V rail... should I be
>>>>>> using a lower voltage so that the logic signals from other devices
>>>>>> like my midi2cv can actually drive the 40530 controls? i.e. Should I
>>>>>> run it at 5V instead?
>>>>>>
>>>>>> Do I need any kind of trigger conditioning off of the reset jack?
>>>>>> e.g. filter? schmitt trigger?
>>>>>>
>>>>>> cheers,
>>>>>> Danjel
>>>>>>
>>>>>>
>>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>
>>
>
>