Well, thanks for using the schematic view of F**ing. That is much better than the usual breadboard view. Is it possible to use ground symbols for all the ground connections?
You’re welcome; sure; and inlined:
I understand the “involate” area but can you be sure that there’s no other connections there? I would hate to see +12V on S1 because it’s still connected to (and controlling) some other device.
For that specific switch, there are no other connections. (Not 100% sure of the other two switches, but will triple-check all external connections before finalizing this project’s design.)
What’s the input voltage tolerance on the LM2575? Can it handle the +36 -24V range? It is definitely worth considering a fuse between the input power and your stuff - make sure the fuse rating is low enough to blow before D0 blows. I like to use a P-type MOSFET on the input power, wired so that reverse polarity switches the MOSFET off, protecting the circuit. Then I don’t need diodes at all.
Personally, I use the Pololu switching regulators to replace the entire blue area of your diagram. They are simple 3-terminal devices (or 4-terminal for the ones with a shutdown input, but you don’t have to connect to that pin.) They are pretty reliable within the automotive voltage range, although I haven’t tested them to the limits.
I appreciate your comments on this. I’ve seen mention of Pololu. I’ve redesigned the power supply section to use one of these (again, Fritzing doesn’t have one of those, but the LM2931 is a reasonable way to represent one). What I’m not sure of at the moment is what to use for the protection MOSFET. I chose the IRF9Z34N because I have a few of them, but would be happy to sub in something that eliminates the need for D0c and R0…
The high-side drive to the output load (yellow area) is not going to work like that.
I’m aware of this. For me (perhaps less so for others) this is a trickier area and will be addressed later on (likely in a separate topic).
I don’t understand the switch logic. Two switches, either of which supplies power but only one is connected to an Arduino input. Normally you would power the Arduino from the car’s “ignition” or “Acc” circuit which is on when the key is on. Then the switches are only control inputs and don’t carry the power supply current.
You’re absolutely right. A few points:
- there will be a 1A fuse added before Q0b, as well as a 7.5A fuse after each of JP6 and JP7
- the +V switch (S7; was S2) is indeed IGN (+12V when ignition is on)
- I got the other +V switch (S6; was S3) wrong; it’s actually switched to ground like S1 (now S2)
- I need S6 to provide “parallel” power to that provided via S7 (not to worry; there is a method to this apparent logical madness ). So, I did a little digging and came up with the green area. Unfortunately, this doesn’t work; as soon as I close S2, the Uno’s main power LED goes dim - I’m pretty sure this was a prelude to the potential release of some magic smoke and likely curtailed longevity of the Uno.
- My intent is to provide the “power up” info for S6 and S7 to the Arduino so I know which is powering things. (Didn’t think the previous iteration needed the extra clutter seeing as I thought those switches were identical.) I’m not sure either of these are needed; they may be dropped (depends on programming).
Thank you for your ongoing comments, suggestions, et al, Morgan.