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   The Natural Philosopher  wrote:   
   > On 19/01/2024 16:15, Chris Green wrote:   
   > > When you power down a Pi is there any simple way to protect inputs   
   > > which are being driven by externally powered equipment?   
   > >   
   > > I have A2D devices on the I2C bus which are powered from the Pi, if   
   > > the Pi has power removed the A2D's will be unhappy I think as their   
   > > inputs will still have the voltages they are measuring applied to   
   > > them.   
   >   
   > ??? If they are powered from the pi, how can they still have voltage?   
   > ?? if they are on the I2C bus, how are they connected to the A2D inputs   
   > on the Pi?   
      
   They are ADs1116 I2C devices on the I2C bus.  Their VDD suppy comes   
   from the Pi, their inputs come from whataver they are measuring which   
   doesn't get turned off whe n the Pi is turned off.   
      
      
   > >   
   > > Similarly I may have one or two logic inputs which are driven by   
   > > external signals (to see if things are turned on for example) and   
   > > these inputs will still be there (at 3.3v logic levels) when the Pi is   
   > > powered down.   
   > >   
   > > Would diode clamps to the Pi's 3.3v supply be OK or are there better   
   > > ways?   
   > >   
   >   
   > I suspect those already exist internally.   
   > It is more relevant to prevent those getting smacked with high current.   
   >   
   > a small resistor would limit any current   
   >   
   Yes, the ADS1115 has internal diode clamps but it does say in the   
   datasheet that external Schottky diode clamps are recommended.   
      
   --   
   Chris Green   
   ·   
      
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