<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
font-size:11.0pt;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal>I have an Arduino-based module, with a GATE input protected by 1K input resistor then clamping diodes to 0V & +5V.<o:p></o:p></p><p class=MsoNormal><a href="https://shedsynth.files.wordpress.com/2021/05/adsr-a-schematic-gate-to-d2.png">https://shedsynth.files.wordpress.com/2021/05/adsr-a-schematic-gate-to-d2.png</a><o:p></o:p></p><p class=MsoNormal>I find that with power off to that module any GATE or CV to the input can pull up the module's +5V through the diode and even power the whole case's +5V rail.<o:p></o:p></p><p class=MsoNormal>The clue was seeing the case’s +5V LED flashing in time with the GATE input.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>And I think that if the input is more than +5V, the un-powered voltage regulator will not be able to regulate so digital components (and perhaps the voltage regulator itself) might be damaged.<o:p></o:p></p><p class=MsoNormal>Have I understood this correctly?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I'm wondering whether to put a 5.1V zener across the module's 0V and +5V to catch any over-voltage.<o:p></o:p></p><p class=MsoNormal>Have I understood THAT correctly?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks in advance,<o:p></o:p></p><p class=MsoNormal>Al<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='mso-fareast-language:EN-GB'><a href="https://shedsynth.wordpress.com/">SHEDSYNTH</a> – home-knitted eurorack<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>