If i have understood this, you using the 7805 as a Constant Current generator and the 555 to provide detection of upper and lower limits (from its internal divider and comparator)
Correct, to the standard 555 astable multivibrator: All I'm doing is replacing the charging resistor with a CC(78L05), then buffering the linear ramp produced - in the more complex (slightly) circuit.
Shouldn't diode D1 be in series with the 12.5V source? The way it is, if someone hooked up power in reverse, D1 would be forward biased with no current limitation. D1 would probably blow and end up not protecting the circuit at all.
Thank you for making that point. You are absolutely correct: If a circuit expects a certain supply Voltage and the supply can provide a Volt spare - a series, reverse protection, diode is by far the best way to go. The 0.7VDC drop (silicon) and its power dissipation will be no problem, however, if a battery is used and the circuit supply requirements are critically close to the supply, then a parallel supply diode with a supply fuse (most important!) can be used - zero Voltage drop. As I mentioned in the video, "I always use a Poly-fuse in the supply" and I used a 12VDC battery. In practice, there's usually a small Voltage drop across any fuse. If the supply is reversed - D1 will go into conduction, Poly-fuse will quickly open up (heat up) and the circuit is protected. Today, there are many options to solve this issue: Power MOSFET, Schottky diode and crowbar to name but a few. That Poly-fuse has saved my bacon on many occasions :)
If i have understood this, you using the 7805 as a Constant Current generator and the 555 to provide detection of upper and lower limits (from its internal divider and comparator)
Correct, to the standard 555 astable multivibrator: All I'm doing is replacing the charging resistor with a CC(78L05), then buffering the linear ramp produced - in the more complex (slightly) circuit.
@@beamer.electronics i have been in electronics from the age of 12 or so... made I it my profession now in IT
Shouldn't diode D1 be in series with the 12.5V source? The way it is, if someone hooked up power in reverse, D1 would be forward biased with no current limitation. D1 would probably blow and end up not protecting the circuit at all.
Thank you for making that point. You are absolutely correct: If a circuit expects a certain supply Voltage and the supply can provide a Volt spare - a series, reverse protection, diode is by far the best way to go. The 0.7VDC drop (silicon) and its power dissipation will be no problem, however, if a battery is used and the circuit supply requirements are critically close to the supply, then a parallel supply diode with a supply fuse (most important!) can be used - zero Voltage drop. As I mentioned in the video, "I always use a Poly-fuse in the supply" and I used a 12VDC battery. In practice, there's usually a small Voltage drop across any fuse. If the supply is reversed - D1 will go into conduction, Poly-fuse will quickly open up (heat up) and the circuit is protected. Today, there are many options to solve this issue: Power MOSFET, Schottky diode and crowbar to name but a few. That Poly-fuse has saved my bacon on many occasions :)