Circuit monitoring question
Despite beign the noob I am in electronics and circuits, I'm trying to whip up a circuit that lights up a 10 digit LED bar graph from a thermal sensor. That, in of itself, isn't a big deal. A resistor here and there, and off we go.
The problem I've run in to is that the probe in question is already part of another circuit, which is monitored via a third party control unit. I'm trying to find a way to tap into the existing circuit with as little effect on the existing circuit as possible. Right now, maximum variance is +/-4% ohms on the received input at the controller for the current circuit (baseline is 2460 ohms for a 20C reading to 142 ohms at 110C, exponential). I think it runs off a 3V circuit, though I don't have that spec at hand at the moment (just the resistance values).
I could run an entirely new sensor just for my circuit, but that'd triple the cost as I'd have to use kinda pricey rugged sensors. I'd prefer it if I could simply tap the existing sensor feed. I'm thinking of maybe using a volatile digital potentiometer, having its wiper somehow controlled by the voltage of the existing circuit. My circuit will be self powered, so my biggest concern in that case is the wiper causing too much resistance on the existing line (maybe a tiny voltage booster circuit to overcome the natural potentiometer resistance?). That, and I have near zilch experience in EE with ICs and only rudimentary experience with analog circuits. I'm not sure how I'd wire it up.
Another idea I just had was to use some transistors and/or comparator ICs. But I still worry about excessive resistance, even if the components are powered external to the existing circuit.
Finally, I might consider just running my circuit 100% in line with the existing one. Intercept the output from the thermal sensor, use it's value to light my bar graph, then use a voltage booster circuit or IC (or some creative math and component use in my circuit) to ensure that the output back to the control unit is kosher.
Any ideas/opinions/tips? My last option seems the best, though most complex and I dunno how the main controller would react to a PWM voltage booster when it expects nothing but a resistive thermal sensor.
Thanks for the help.