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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Thank you to everybody who replied.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>I want to use both GATE inputs and CV inputs to Arduino analog inputs, I apologise for my previous misleading diagram.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>I have also thought of a likely use-case: using a drum machine as GATE input or an external controller as CV input, and switching those on before the modular rack.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>I have now decided to go with this plan rather than the transistor idea:<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><img width=215 height=143 style='width:2.2395in;height:1.4895in' id="Picture_x0020_3" src="cid:image001.png@01D76431.8BB3A3E0"></span><span style='mso-fareast-language:EN-US'><o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><a href="https://shedsynth.files.wordpress.com/2021/06/input-protection-schematic-clampzener.png">https://shedsynth.files.wordpress.com/2021/06/input-protection-schematic-clampzener.png</a><o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>I’ve been testing this, risking life and limb and a £3 Arduino Nano.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>When the module is powered: the Schottky diodes clamp neatly to the 0V and +5V rails and the Zener stays quiet.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>When the module is not powered: if -ve voltage the lower diode clamps and if +ve the Zener catches it.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>In this case the Nano (& other components) might flicker into life as the input gets above 3V, but mine seems to have survived so far.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>The transistor circuit had 3 disadvantages:<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>1: When the module is not powered: the Arduino input could be +0.7V, greater than the Vcc + 0.5V limit.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>2: Analog inputs were compressed as the transistor turned on.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>3: The trimmer adjustment would be risky.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Thanks yet again,<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Al<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US>From:</span></b><span lang=EN-US> John Luciani <jluciani@gmail.com> <br><b>Sent:</b> 16 June 2021 19:14<br><b>To:</b> ShedSynth <shedsynth@gmail.com><br><b>Cc:</b> *SYNTH DIY <synth-diy@synth-diy.org><br><b>Subject:</b> Re: [sdiy] Will clamping diode work when power is off?<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><p class=MsoNormal>Rather than a transistor + resistor I would use a diode connected<o:p></o:p></p></div><div><p class=MsoNormal>between +5V (cathode) and Arduino input (anode). I also like to <o:p></o:p></p></div><div><p class=MsoNormal>split the series resistance so that one resistor will limit the<o:p></o:p></p></div><div><p class=MsoNormal>current from the input through the diodes and the second limits the current from<o:p></o:p></p></div><div><p class=MsoNormal>a clamped condition into the Arduino input.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>John L<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Wed, Jun 16, 2021 at 12:53 PM ShedSynth via Synth-diy <<a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a>> wrote:<o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><div><p class=gmail-m-7100488788987173473msoplaintext>I hope you won't mind me exhuming my old question again.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>My friend Tim suggested using a BC557 to actively clamp the input to the supply rail:<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext><img border=0 width=345 height=183 style='width:3.5937in;height:1.9062in' id="gmail-m_-7100488788987173473Picture_x0020_1" src="cid:image002.png@01D76431.8BB3A3E0"><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext><a href="https://shedsynth.files.wordpress.com/2021/06/adsr-a-schematic-gate-to-d2-2-2.png" target="_blank">https://shedsynth.files.wordpress.com/2021/06/adsr-a-schematic-gate-to-d2-2-2.png</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>If the voltage on the emitter goes above the voltage on the base (+5V when the module is powered, 0V when not powered) the transistor will conduct to ground, clamping the input.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I believe it will clamp to Vbe (about 0.7V) above the base voltage, so I planned to use a preset resistor P1 to set the clamp within the safety limit of the Arduino inputs (VDD + 0.5V).<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I’d be interested in comments, particularly about behaviour when the circuit isn’t powered – the original question.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Thanks,<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Al<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>-----Original Message-----<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>From: ShedSynth <mailto:<a href="mailto:shedsynth@gmail.com" target="_blank">shedsynth@gmail.com</a>> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Sent: 30 May 2021 09:16<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>To: mailto:<a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Subject: RE: [sdiy] Will clamping diode work when power is off?<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Thank you to everybody for the replies.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I have previously experimented with a 5.1V Zener across Arduino inputs: GATE inputs triggered successfully but CVs appeared not to be read linearly by the analog inputs.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I'll experiment with clamping each input through diodes to a Zener to 0V, if I understood that suggestion correctly.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I'll experiment to measure current through a Zener across 0V and +5V when the module is powered normally.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I hadn't understood the reason for the diodes across voltage regulators.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>The use-case is that I have two boxes which share the same 19V DC supply and are normally switched on and off together as a single unit.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I noticed the issue when I switched off the second box to fiddle with a module under test, while it was still connected to the CV from an LFO module in the first box.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>To me this seems like a common risk when fiddling, less so when actually playing any music (and for me that ratio is about 90/10%).<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>I want to mitigate against likely mistakes in the expected range -12V to +12V.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>So far I seem to have got away with it, although I'm now trying to remember when and how I broke the voltage regulator in the only Arduino that has failed on me so far - that still works on USB power, not on +12V.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Spotting the issue, and your replies, has helped me understand some fundamentals.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Thank you all again,<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Al<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>-----Original Message-----<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>From: Synth-diy <mailto:<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank">synth-diy-bounces@synth-diy.org</a>> On Behalf Of MTG<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Sent: 29 May 2021 17:46<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>To: mailto:<a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Subject: Re: [sdiy] Will clamping diode work when power is off?<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>This is a cool idea, but I'm curious about the OP's problem. What's the use-case here where part of the rig is powered? Is this just power-on-off timing situation or is powering part of the system a normal part of using it?<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>On 5/29/2021 5:10 AM, S Ridley via Synth-diy wrote:<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> Another option is to invert the gate in the software, use the pin's <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> internal input pull-up and use an npn transistor to switch it to 0v.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> I suppose current might flow through the BC junction if the power is <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> off, but you'd be using a much higher base resistor on the input so <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> current through that route can be minimised.<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> Steve<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>> <o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>_______________________________________________<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Synth-diy mailing list<o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>mailto:<a href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank">http://synth-diy.org/mailman/listinfo/synth-diy</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext>Selling or trading? Use mailto:<a href="mailto:marketplace@synth-diy.org" target="_blank">marketplace@synth-diy.org</a><o:p></o:p></p><p class=gmail-m-7100488788987173473msoplaintext> <o:p></o:p></p></div></div><p class=MsoNormal>_______________________________________________<br>Synth-diy mailing list<br><a href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a><br><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank">http://synth-diy.org/mailman/listinfo/synth-diy</a><br>Selling or trading? Use <a href="mailto:marketplace@synth-diy.org" target="_blank">marketplace@synth-diy.org</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><br clear=all><o:p></o:p></p></div></div></body></html>