hello! this is my first post here, hope i'm doing it right.
this is my first "true" project using precision analog, and thus don't really know the best solution to my problems.
i'm designing a current meter (based on the uCurrent but different). the uCurrent uses a slide switch to change between ranges (uA,mA,nA). A similar project to my own,the current ranger, uses p-channel mosfets. however i don't want either of those solutions. my idea would be to use a pair of relays to control the ranging.
here is a picture of the uCurrent range switch:
since this device will be optically isolated (thus battery powered) (the microcontroller is usb powered), mosfets would be ideal. however the relays coil legs cross the isolation barrier nicely, so could be powered with usb 5v.
here is my sad excuse for a block diagram:
simply explained, the window comparator has two outputs, so those pass through the optocoupler to the micro. the micro then decides to range up, down, or stay the same. the relay is powered on the USB side, thus no extra battery drain (usb should have enough power)
relay will be this: tx2-5v
my questions are:
-is this a good solution (relays)
-will i have noise issues?
-will the relay ranging be fast enough to not blow the ADC?
this is my first "true" project using precision analog, and thus don't really know the best solution to my problems.
i'm designing a current meter (based on the uCurrent but different). the uCurrent uses a slide switch to change between ranges (uA,mA,nA). A similar project to my own,the current ranger, uses p-channel mosfets. however i don't want either of those solutions. my idea would be to use a pair of relays to control the ranging.
here is a picture of the uCurrent range switch:
since this device will be optically isolated (thus battery powered) (the microcontroller is usb powered), mosfets would be ideal. however the relays coil legs cross the isolation barrier nicely, so could be powered with usb 5v.
here is my sad excuse for a block diagram:
simply explained, the window comparator has two outputs, so those pass through the optocoupler to the micro. the micro then decides to range up, down, or stay the same. the relay is powered on the USB side, thus no extra battery drain (usb should have enough power)
relay will be this: tx2-5v
my questions are:
-is this a good solution (relays)
-will i have noise issues?
-will the relay ranging be fast enough to not blow the ADC?