Hi all,
I'm brand new here, but I figured maybe I could learn a bit from you guys.
I've been trying to figure out how the voltage monitor system from my 1987 Volkwagen Westfalia Camper Van works. Here is the circuit board:
And this is the schematic that I've drawn out for it:
So, first things first. I assume that the blue cylindrical object between the red LED and the potentiometer is a diode (labeled D3 in schematic/picture), would I be correct? I show a .7V drop with my Fluke 113 multimeter, but there is no single beep as I get with the other 2 diodes on the board. I show 0L when I test it reverse biased.
OK, The point of the circuit is to take the voltage from the camper battery (12V nominal), and illuminate either the Green, Yellow, or Red LED's corresponding to the charge state (voltage).
So here's how I *think* this is supposed to work. The voltage drop across diode "D2" is a constant 0.578 volts (measured w/ Fluke 113). So theoretically the non-inverting voltage of the top op amp should be 0.578 volts higher than the non-inverting voltage at the bottom op amp.
Here's where I get confused: Because of the reverse biased diode, "D3", there should be no current running across this part of the circuit, and therefore the voltage at top op amp should be the same as the voltage after D1. But this would insure that the top op amp is always outputting V, and thus the Green LED would never illuminate. What am I missing?
Jumping to the inverting (-) inputs, based on the measured potentiometer values, I calculated a voltage drop of 17% of V, or Vp = 0.83*V.
For the system as a whole, this is what I gather: The difference between the inverting (-) inputs of the op amps is scaled linearly with any change in V, whereas the difference between the non-inverting (+) inputs stays constant. It's this difference that causes the circuit to change characteristic when the absolute voltage V increases/decreases.
Any help on this would be greatly appreciated regarding what D3 actually is, and what voltages are to be expected at the non-inverting (+) inputs to the op amps.
Thanks
I'm brand new here, but I figured maybe I could learn a bit from you guys.
I've been trying to figure out how the voltage monitor system from my 1987 Volkwagen Westfalia Camper Van works. Here is the circuit board:
And this is the schematic that I've drawn out for it:
So, first things first. I assume that the blue cylindrical object between the red LED and the potentiometer is a diode (labeled D3 in schematic/picture), would I be correct? I show a .7V drop with my Fluke 113 multimeter, but there is no single beep as I get with the other 2 diodes on the board. I show 0L when I test it reverse biased.
OK, The point of the circuit is to take the voltage from the camper battery (12V nominal), and illuminate either the Green, Yellow, or Red LED's corresponding to the charge state (voltage).
So here's how I *think* this is supposed to work. The voltage drop across diode "D2" is a constant 0.578 volts (measured w/ Fluke 113). So theoretically the non-inverting voltage of the top op amp should be 0.578 volts higher than the non-inverting voltage at the bottom op amp.
Here's where I get confused: Because of the reverse biased diode, "D3", there should be no current running across this part of the circuit, and therefore the voltage at top op amp should be the same as the voltage after D1. But this would insure that the top op amp is always outputting V, and thus the Green LED would never illuminate. What am I missing?
Jumping to the inverting (-) inputs, based on the measured potentiometer values, I calculated a voltage drop of 17% of V, or Vp = 0.83*V.
For the system as a whole, this is what I gather: The difference between the inverting (-) inputs of the op amps is scaled linearly with any change in V, whereas the difference between the non-inverting (+) inputs stays constant. It's this difference that causes the circuit to change characteristic when the absolute voltage V increases/decreases.
Any help on this would be greatly appreciated regarding what D3 actually is, and what voltages are to be expected at the non-inverting (+) inputs to the op amps.
Thanks