I would like to build a circuit to perform a timed shutdown, based on logic inputs from headlamp wires and ignition wires.
I have decided on PIC10F200 (datasheet) to perform the logic.
I also have many spare 7805 linear regulators, so thought I'd use those to perform 12V->5V regulation before connecting directly to PIC pins configured as inputs. Is this a terrible idea? I have added pulldown resistors so that the PIC input pins can read defined values.
Using Fritzing, i've created a circuit:
I'm still tinkering at the moment, and this being my first PIC circuit, I want to make sure I can avoid all the possible traps when working in an environment like this.
So basically, is the circuit okay, or have I overlooked things?
All and any help appreciated, please go easy on me. I'm new!
Update:
Following advice from Olin and Wouter, I now have this:
Is this ok?
Olin says making use of the weak pullups on the PIC could save on component count, yhis is how i've interpreted him: This works in the simulator, but I've no idea if my pile of BC547 are suitable!
I also don't know which to choose, or why?
Thanks again guys.
Answer
You can use 7805's this way, but as they only replace one resistor (and require 2 additional decoupling capacitors each!) I would never do it this way. My suggestions:
- replace the two 'sensor' 7805's by resistor / zener-diode combinations. Use 4v7 zeners.
- add two 100nF capacitors at the input and utput of the remaining 7805
- add a suppressor diode over the relays coil!!
- I am not sure a jellybean 7805 is a good idea in an automotive environment, there can be nasty spikes on the power line.
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