Hi, I joined this forum with the hopes of someone being able to help with a project of mine.

I'm working for a client building a racecar, my speciality being suspension not electronics or engines, and in discussion we decided we wanted to put a digital display to show a readout on the dashboard, from a sensor on the engine (lambda sensor). While I am relatively confident, with a bit of time and work I could make a glorified Voltmeter that simply showed the Voltage of the sensor I'd really like to take that voltage and display the actual value but I am not entirely sure how you do this? Is it possible without the use of a micro-controller or is that the best way forward?

 

yes you can use an op amp to amplify it to your desired voltage and use a moving coil meter or digital display.

 

yes you can use an op amp to amplify it to your desired voltage and use a moving coil meter or digital display.

That's a start. I take it I'll need to match the new voltage to the value I'm trying to display? My plan was to use an analogue to bcd converter that then fed into 7 segment displays.

Here's the tricky part though. The way the sensor works at 0.5V the reading should be 1.00 but when the voyage increases to say 0.6V the reading should say 0.8 not 1.2 as would be expected. Is there a way of inverting the voltage around a datum point. So a 0.1V increase on the input sensor would result in a 0.1V decrease on the display?

 

An op-amp can do that as long as your relationship between input and output is linear. You need to adjust slope and intercept, but that't what op-amps circuits are good at. If you have some nonlinear relationship, it would be easier to use a microcontroller and program in the calibration curve.

 

So a 0.1V increase on the input sensor would result in a 0.1V decrease on the display?

You would want an inverting amplifier with a gain of 1 (Rf = Rin) to accomplish what you describe. See wiki link for description: http://en.wikipedia.org/wiki/Operational_amplifier_applications

 

Wideband or narrow band O2 sensor?
No point in a display for a narrow band as its going to just bounce all over constantly. Unless you just need to know when you are (if you are) running in closed or open loop fuel maps and even then. Plus there are plenty of "blinky light gauges" as I call them out there for that or even just volt meter displays but its useless information mostly.. no point in building your own when you can get them for cheap already in a gauge pod or whatever..

widebands will give more accurate/usable information and again there are displays out there for that already.. ones with logging functions,etc...
check here and more http://www.innovatemotorsports.com/

 

Excellent. Thanks for your help. Op Amps are not on tomorrow nights reading list.

I'm aware of these types of gauges. I've learnt a few things working in motorsport, you can always do it yourself better, for less (if you're a good engineer that is). Not only are you pretty much stuck with there design of lovely "fast and furious" type gauge design but you have no real understanding of what it's doing to trust what it says or why. At least if my design is wrong I'll be able to determine why and adjust accordingly.

 

so wideband or narrow?
and its the sensor/heater already being powered/used by an ECU?

 

Well as you said Narrow band isn't really about precision. Your either Rich/Lean or Stoich. It should be a Wideband fitted atm as it feeds into a ignition ecu. Forgot to mention I think that this car is on carbs so no real ecu.