Greetings all and Happy New Year!
I've been working on a logic circuit to control the main entrance gate at our ranch for some time now. I've been testing using Falstad's Circuit Simulator.
However, I've run into a problem: In the control head, I need to implement some simple logic to turn on the "STOPPED" indicator when the main entrance gate is not at the open limit (open limit = NOT grounded) AND not at the closed limit (closed limit = NOT grounded), OR when the "STOP" button is pressed (sending 12V to the latch interrupt relay).
I'm going to admit right up front that I have very little electronics knowledge compared to most people out here, but that hasn't stopped me from trying - smiles.
Let me post what I have first, and then I will explain the dilemma:
In the above schematic, I can see the Q3 transistor is forward biased even when all inputs are zero, and I fail to understand why.
I'm also not sure if I have the saturation points set correctly.
And lastly, not matter what I do, I cannot make the current draw of the LED equal to exactly 10 mA in all scenarios - it's close, but I'd like to know if there is a solution where it is always exactly 10 mA.
It DOES work....just not perfectly. Q1, Q2, and Q3 are all 100 hFE transistors, and power consumption is a factor since this is all solar powered.
Appreciate any help on this.
I'm really interested in other's thoughts and ideas as I am sure there is more than a couple of solutions to this problem.
AnalogKid nailed it. Can't thank you enough.