> Yes, you could. I try to do what I think will work best instead of what will use the fewest parts.
Sure. Tou seem to have very strong feelings against that first design: you said it's like begging for something to go wrong! Do you think things could mess up easier that way?
>> why are the middle boxes connected differently from the low ones?
> Because there's four ranges: below low, below medium, above medium, and above high.
Sure, but the rules to light yellow and red (connected to middle and low boxes) are similar -- i.e., if there is a signal below a certain threshold, the respective light turns on. So, since the middle outputs are connected to gnd via diodes, why shouldn't the red outputs go to gnd through diodes as well? When red is on, all the current flowing from the led is going into the comparator output (at 0V, of course) instead of going directly to gnd? So why don't you do the same with the yellow?
And just to make sure I understand things here:
- the high comparators should give +12 when one signal is above high
- the middle comparator should give 0 when one signal is below medium
- the low comparator should give 0 when one signal is below low
therefore all comparators should be conected with the threshold on the - input and the signal on the +.
>> I'd like to use lights of higher power than a LED (something around a few watts). Could I use relay+diode instead of a LED?
> Depending on the relay, the op-amps may not be able to do it. The datasheet for the TL084 says that the relay will need to have a resistance of at least 1000 ohms. I'm not so sure of that, I wouldn't be surprised if they could go as low as 300, in particular they won't even light those LEDs very well if they can't. (maybe they can't, I didn't test it...) I've seen datasheets that claim that the output current a TTL chip isn't enough to drive one of it's inputs, so I don't take datasheets too seriously. I think they just muck up the numbers in them so that if they sell you a broken chip they can say "we never said it would work that well" or something like that. The datasheet also says that you can short the outputs to ground continuously, so it won't break the chips at least, but what's important I suppose is wether or not the lights come on.
> You could probably swap the LEDs out for transistors (and change those 330 ohm resistors to 10k), then have those transistors switch some other transistors (otherwise the relay current still goes through the op-amps) and then have those transistors switch the relays, which would be the safe way to do it.
Why would just the relay be unsafe? And isn't the whole thing just a matter of searching parameter tables?
Oh, and what happens if the output signal should be above supply? This is the saturation that leads to a output = +Vsupp?
Sure. Tou seem to have very strong feelings against that first design: you said it's like begging for something to go wrong! Do you think things could mess up easier that way?
>> why are the middle boxes connected differently from the low ones?
> Because there's four ranges: below low, below medium, above medium, and above high.
Sure, but the rules to light yellow and red (connected to middle and low boxes) are similar -- i.e., if there is a signal below a certain threshold, the respective light turns on. So, since the middle outputs are connected to gnd via diodes, why shouldn't the red outputs go to gnd through diodes as well? When red is on, all the current flowing from the led is going into the comparator output (at 0V, of course) instead of going directly to gnd? So why don't you do the same with the yellow?
And just to make sure I understand things here:
- the high comparators should give +12 when one signal is above high
- the middle comparator should give 0 when one signal is below medium
- the low comparator should give 0 when one signal is below low
therefore all comparators should be conected with the threshold on the - input and the signal on the +.
>> I'd like to use lights of higher power than a LED (something around a few watts). Could I use relay+diode instead of a LED?
> Depending on the relay, the op-amps may not be able to do it. The datasheet for the TL084 says that the relay will need to have a resistance of at least 1000 ohms. I'm not so sure of that, I wouldn't be surprised if they could go as low as 300, in particular they won't even light those LEDs very well if they can't. (maybe they can't, I didn't test it...) I've seen datasheets that claim that the output current a TTL chip isn't enough to drive one of it's inputs, so I don't take datasheets too seriously. I think they just muck up the numbers in them so that if they sell you a broken chip they can say "we never said it would work that well" or something like that. The datasheet also says that you can short the outputs to ground continuously, so it won't break the chips at least, but what's important I suppose is wether or not the lights come on.
> You could probably swap the LEDs out for transistors (and change those 330 ohm resistors to 10k), then have those transistors switch some other transistors (otherwise the relay current still goes through the op-amps) and then have those transistors switch the relays, which would be the safe way to do it.
Why would just the relay be unsafe? And isn't the whole thing just a matter of searching parameter tables?
Oh, and what happens if the output signal should be above supply? This is the saturation that leads to a output = +Vsupp?