On Sunday 10 Mar 2013 19:50:40 James Courtier-Dutton wrote: > As I will be doing ADC on Mains input voltage, I will be adding a > digital isolation on the SPI bus. > E.g. ti iso7241 Yep, that looks fine.
> So the ADC will be on the 240V AC side, but then the raspberry PI will > be protected by the digital isolation by having the isolation on the > link between the ADC and the PI. ADC -> Isolation -> SPI Bus of > PI. Don't forget you'll have to feed the ADC 3.3 Volts somehow. > > This also improves the accuracy and simplicity of the ADC side, no > isolation transformers, and uses less power to measure it. You could use a potential divider (two resistors) as an input stage, feeding an optocoupler (low-voltage AC side), which then switches 3 volts to the ADC. Add suitable protection diodes and filter capacitors as required. This will give an on/off sense, but no effective voltage measurement. If you want voltage measurement, you'll need a potential divider and a summing amplifier to get a 0-3v signal which you can then sample. For current measurement, look at current transformers, followed by a suitable amplifer stage. Hope this helps, Tim B. -- Hampshire Linux User Group Chairman -- Please post to: Hampshire@mailman.lug.org.uk Web Interface: https://mailman.lug.org.uk/mailman/listinfo/hampshire LUG URL: http://www.hantslug.org.uk --------------------------------------------------------------
