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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoPlainText>I hope you won't mind me exhuming my old question again.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>My friend Tim suggested using a BC557 to actively clamp the input to the supply rail:<o:p></o:p></p><p class=MsoPlainText><img width=345 height=183 style='width:3.5937in;height:1.9062in' id="Picture_x0020_1" src="cid:image001.png@01D762D7.54490040"><o:p></o:p></p><p class=MsoPlainText><a href="https://shedsynth.files.wordpress.com/2021/06/adsr-a-schematic-gate-to-d2-2-2.png">https://shedsynth.files.wordpress.com/2021/06/adsr-a-schematic-gate-to-d2-2-2.png</a><o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Thanks,<o:p></o:p></p><p class=MsoPlainText>Al<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>-----Original Message-----<o:p></o:p></p><p class=MsoPlainText>From: ShedSynth <mailto:shedsynth@gmail.com> <o:p></o:p></p><p class=MsoPlainText>Sent: 30 May 2021 09:16<o:p></o:p></p><p class=MsoPlainText>To: mailto:synth-diy@synth-diy.org<o:p></o:p></p><p class=MsoPlainText>Subject: RE: [sdiy] Will clamping diode work when power is off?<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Thank you to everybody for the replies.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>I hadn't understood the reason for the diodes across voltage regulators.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText>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=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>I want to mitigate against likely mistakes in the expected range -12V to +12V.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Spotting the issue, and your replies, has helped me understand some fundamentals.<o:p></o:p></p><p class=MsoPlainText>Thank you all again,<o:p></o:p></p><p class=MsoPlainText>Al<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>-----Original Message-----<o:p></o:p></p><p class=MsoPlainText>From: Synth-diy <mailto:synth-diy-bounces@synth-diy.org> On Behalf Of MTG<o:p></o:p></p><p class=MsoPlainText>Sent: 29 May 2021 17:46<o:p></o:p></p><p class=MsoPlainText>To: mailto:synth-diy@synth-diy.org<o:p></o:p></p><p class=MsoPlainText>Subject: Re: [sdiy] Will clamping diode work when power is off?<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>On 5/29/2021 5:10 AM, S Ridley via Synth-diy wrote:<o:p></o:p></p><p class=MsoPlainText>> <o:p></o:p></p><p class=MsoPlainText>> Another option is to invert the gate in the software, use the pin's <o:p></o:p></p><p class=MsoPlainText>> internal input pull-up and use an npn transistor to switch it to 0v.<o:p></o:p></p><p class=MsoPlainText>> I suppose current might flow through the BC junction if the power is <o:p></o:p></p><p class=MsoPlainText>> off, but you'd be using a much higher base resistor on the input so <o:p></o:p></p><p class=MsoPlainText>> current through that route can be minimised.<o:p></o:p></p><p class=MsoPlainText>> <o:p></o:p></p><p class=MsoPlainText>> Steve<o:p></o:p></p><p class=MsoPlainText>> <o:p></o:p></p><p class=MsoPlainText>_______________________________________________<o:p></o:p></p><p class=MsoPlainText>Synth-diy mailing list<o:p></o:p></p><p class=MsoPlainText>mailto:Synth-diy@synth-diy.org<o:p></o:p></p><p class=MsoPlainText>http://synth-diy.org/mailman/listinfo/synth-diy<o:p></o:p></p><p class=MsoPlainText>Selling or trading? Use mailto:marketplace@synth-diy.org<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p></div></body></html>