Planning to build a quadruple indicator for automotive (lambda) oxygen sensors outputted voltage with four LM3914 in dot mode in 0.1 to 0.9 V scale.
Wondering what is the typical load these sensors work happily with ?
I believe the LM3914 is over 20K input resistance, but cannot tell for sure. Do you know that too ?
I've messed with these, the impedance is quite low for a standard zirconia sensor, a titania sensor on the other hand has a sensing element in series with a resisitor and is a higher impedance.
Are you using a standard hego sensor or something else?
You can buffer the o/p with a non inverting op amp if you like.
Problems are more likely to occur if your tapping into a lambda sensor allready used by an existing engine control system.
If I remember rightly your aiming for an o/p of 0.6v which corresponds to a stoichometric ratio of 14.7 to 1, unless your burning alky or soemthing exotic.
Thanks, gentlemen.
That data sheet helps a lot, good find.
Yes, plan is to tap onto existing standard operating sensors wiring for an on-board permanent monitor display. Will see what happens. So far a 1 MΩ oscilloscope probe does not seem to load the signal, sensors appear to be low enough source resistance.
After about 7 minutes watching 4 LM3914's bounce up and down, you'll get bored. The only notable observation I saw was when the engine was at WOT where you should see a rich condition. If it is lean, pistons will be consumed.
I have a 2 channel unit that I made, never used it. You are welcome to it just for the cost of postage. Prior to making that, I would Duck Tape my Fluke to windshield for readings.
I built one way back that used the same circuit for displaying injector pulse width or lambda, impressed my mates at the time.
You can diode or the lower leds to a buzzer to warn of lean out.
You will get some fluctuation up and down due to cross mapping, but thats a good thing when the sensor fouls up you'll see this slow down.