I want to use this little device http://www.dataq.com/products/startkit/di194rs.htm to plot wide band O2 vs RPM but I need to convert the rpm signal to volts so the dataq can plot it.Im no electric wiz so it has to be a simple circuit or I was thinking of just buying a aftermarket digital tach and hoping the display runs off of a voltage of 0-10v.If any body knows how to I could work this out let me know.

 

Can somebody that is good with circuits looks at this and tell me what circuit would be easyest to make to change the tach out put to volts. http://www.national.com/ds/LM/LM2907.pdf

 

Some info on h/w & s/w solutions here:

http://forums.corvetteforum.com/zerothread?id=374249

 

The very first tachometer circuit, or the circuit showing an 8 cylinder example would work for you, although it may not give you a full scale 10V output. I don't know if that is really necessary, since the data aq. unit has 10 bit resolution. If you need to rescale the output of the freq-volt converter, use an op-amp in a non-inverting config, with a gain based on the output voltage. for instance, if the full scale out is 6v, and you want 10 v, the gain would be 10/6, or 1.6. You probably wouldn't need that to chart data, because you can alway assume that 6 volts = some freq. determined by the circuit you build, which correlates to max rpm. If you use 6500 rpm, and the application example, 6v=~406Hz, or 67Hz/V. Hope that helps. the application circuits are pretty straightforward, if you're good with following the schematic and a soldering iron, you should have no trouble.

 

OK say I make the first circuit and I get more than 10V could I just put a trimpot on the output to get it lower?

 

With the first circuit, and a v-8, you wouln't hit 10 v until well over 10,000 rpm, so you wouldn't have to worry about it, and a smaller cylinder engine is even higher rpm. You could use a trimpot to scale the voltage, if you needed to.

 

jwscab thanks for your help when Im done Ill let know how it works out.