Re: How to measure 0-30V with ADC that has 5V maximum input
Hi Giftbox, can you test the LM358 separate to see if is working properly?
It is probably blown by ESD or short circuit or the power polarity connected
reverse. Your circuit is correct. Another thing to keep in mind is that LM324 and LM358
will never output 5Volts with a 5Volt supply due to their output design that subtracts aprox. 1Volt from the max. VCC voltage.
It should be okay up to 4 volts. In this case you have to change the 2K res to around 1k54 I let you do the calculation.
So when your input voltage is 30Volts the divider should output 4Volts. then you have to scale your ADC accordingly.
The simplest is to use a rail to rail single supply opamp, check with National Semiconductors.
Tornado