Michael Ross wrote:
I will probably be implementing a DC battery system for lighting and so on so I can get op amp power from there.
I don't know about your lighting system, but in an EV, the pack is isolated from ground. The voltages you want to measure are "floating" and not ground referenced. You can't power the comparators from a grounded 12v system. You either needed a 12v DC/DC converter with isolated output, or a HVDC-to-low voltage power supply to power the comparators.
Or there is already a converter to 12V on it. I would not use TTL if I can get around it - because it is noise vulnerable. I would likely resort to some optos if noise gets difficult.
From a "do this task" POV, an op amp comparator is exactly the right function.
Technically, the function needed is a window comparator. This uses two comparators. One detects a voltage above the reference, and the other detects a voltage below the reference. But you can get two (or more) comparators inside a single chip (LM393 for example).
However, IC comparators are intended for voltages under 30 volts. It takes a lot of parts to use them to compare higher voltages.
If the difference between the two halves is too great then it warns. if the difference is intermittent then the indication stops. I think I may like this better than a slowly increasing brightness
If you want a hard "digital" on/off indication, use the LED in an optocoupler in place of the red LED in the Batt-Bridge. Use the output of the optocoupler to switch some "digital" device, like logic gate or relay. Or, there are optocoupler with built-in hard-switching digital outputs that could directly switch something on/off.
But in any case... start by precisely defining the problem you wish to solve *without* assuming a solution. Exactly what must the output do? Work backwards from there.
-- If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve. -- Jeff Bezos -- Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
