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But in order for the button to light up, it needs to float at 16V and draws about 40mA. The light draws power from the button contacts when the button is open.
Protecting the logic from 16V is easy, a zener and a resistor.
It's pulling the line up to 16V and letting the button draw 40mA in such a way that the button can be pressed without damaging the 16V supply that is stumping me. Also, I'd like to be able to light 8 buttons off the same 16V supply.
A 100ohm pull up resistor would have to dissipate 2.5W while the button is closed and would cause a 4V drop when the button is opened. Neither is practical. Any ideas on how I could do this?
[...] they don't believe they are kid resistant enough.
But thinking about the design does bring up another puzzler. Same idea, but the button has a Red/Green bi-directional LED across the NO contacts. I would want to be able to control what color the button is (red or green) but still be able to read it, but only need it to be read while it is green. I'm going to think about it tomorrow, but figured I'd ask as well.
Reading the two-way LED is pretty easy, in that one of the pins will either be high or low depending on which way the current is flowing.
Won't tying the button to Q2's base mean the highest the PB_OUT will float is 0.7V? Not easily read by the controller.
The only thing I don't like is that it requires two lines per station and a common vcc and GND rail. So one cat-5 cable could only carry 3 stations. If you tie color and PB_OUT together and remove Q2, then you could use one line to read the button and set color, with the obvious effect that when the controller pulls all button lines low to make the LEDs red, the button could no longer be read, but that is ok. Button presses when audio is playing will be ignored anyway. But I'd still like to also keep the ability for turning the LED off (also don't need the read the button during this time), the original function of Q2. If the controller's logic was tri-state, could you use the High-z state to turn the LED off? Hmm, what about the third state being the controller pulling the button line past the VCC voltage at the controllers, like to 5V.
I think this just turning into a mental challenge if anything. The more i think about it, the more it makes more sense in simplicity just using green LEDS at the stations parallel with the buttons, with switchable pull-ups on the controller to turn them on or off. One custom board to make instead of one for each station.
While I don't see any need for the light to go out while the button is held down(?)
Quote from: Admin on November 28, 2011, 12:23:46 AMReading the two-way LED is pretty easy, in that one of the pins will either be high or low depending on which way the current is flowing.There will always be a voltage drop depending on direction, but the "other end" won't be ground, so how would you read it "pretty easy"?Even worse if the button have to physically short the LED.I don't say it's hard, but "pretty easy" sounds to me like something you can do while on the phone or such