It depends how robust you want the inputs to be. Personally I normally optoisolate 24V inputs - avoids the risk of a wrong value resistor damaging the Pico!I'm looking to design inputs capable of reading up to 24 VDC Looking at some other designs It seems a common one is to use 20K resistors and a 3.3V Zener.
The SkyWorks/Silicon Labs Si838x family of devices are interesting - 8 isolated inputs which are 24V tolerant, parallel or SPI interface.
If you go for the low-cost option, I'd start with a 3V0 zener - typically 5-10% tolerance which will limit the voltage at the Pico to 2.7-3.3V (not that it'll be that accurate, due to the characteristics of the zener).
Dependent on your applications, I'd also aim to support 28-30V everywhere, rather than just 24V (i.e. a nominal 24V lead-acid battery).
I don't normally do 'get away with', so won't comment on the series diode.I'm also Looking at the power side of things and typically I have 4 AA battery or 6VDC power available This is too much for the Pico W to take but is it worth designing/coping a power supply or can I get away with a Diode inline the input power 1N1007 I have a bunch of these left over. If the input power is beyond that I would use a dedicated power supply.
You can get dc-dc converters with wide input range; both as isolated and non-isolated, and as packaged units and chip-based solutions. The chip-based ones tend to be lowest cost, and nowadays its just a matter of plugging requirements into a few formulae to get the necessary component values. PCB layout is a bit fussy, though.
See comments on isolation above.I think I can get away with using a ULN2003A to drive outputs at up to 24 VDC.
Also note that the ULN2003A/ULN2803 has quite a high voltage drop across the output transistors. There are pin-compatible options which use a MOSFET. And there are some isolated options as well.
Statistics: Posted by stevend — Wed Jan 31, 2024 2:12 pm