Oh I see, I didn't tie the grounds together... rookie mistake!Here is a typical application where the output of a 555-timer circuit is used to switch on an NPN transistor.
+VLOAD can be different from +VCC. The load can be an LED, opto-coupler, relay, etc.
View attachment 194383
SW1 is much weirder:Next up is determining what is happening at SW1, so we know which end is being switched in which direction. Same two questions as in #17 for SW1.
- When the TTL level is high (the system is running), open terminal a has 4.92V and terminal b has -0.07V
- When the TTL level is low (the system is shut off), open terminal a has -11.08V (!?) and terminal b has -16.06V (which would change with whatever potential the batteries are storing at the time).
- When closed with the TTL level high (turning system power ON), both have -0.68V
- When closed with the TTL level low (turning system power OFF, both have -15.65V
I hope that doesn't confuse things.
I can take power directly off the system batteries (which are controlled by uC1), which is 12-16V depending on the charge state. I imagine I could wire it in separate from the MOSFET switch so that it's always on.Also, what power is available to run the timer circuit?