Hi, I need to create a completely analog circuit that uses the MQ-3 alcohol gas sensor to determine the BAC of the user (I can use timers like the 555 too). The circuit has to operate between 7 - 9v and should minimise noise and be operationally stable. The output should provide at least a 3 step 'resolution' e.g. sober, tipsy, drunk.

I would like to increase the output resolution and use a led bar graph with 10 steps. The MQ-3 requires +5v DC (or AC), so I think that it would make sense to use a 5v regulator to power the sensor, op-amps, LEDs... I would also like to implement some function that would be able to let the user calibrate the sensor, and provide a warm-up timer (since it takes ~20 sec for the heater to warm up).

If you could provide some ideas about how to implement these functions and filter the signal that would be appreciated (i.e what 'stages' are needed to get a useful output from the sensor).

Thanks

 

(I can use timers like the 555 too). The circuit should minimize noise and be operationally stable. The output should provide at least a 3 step 'resolution' e.g. sober, tipsy, drunk. Thanks

Is this a school assignment? We have a section just for those.

 

Yep, should it be under the "Homework Help" section?

 

I'll tell the boss.

 

Meanwhile...https://www.sparkfun.com/products/8880
I wonder if an LM3914 is the chip I'm thinking about.

 

Not the boss, more like one of the head grunts.

 

It just sounds so much better to call you the boss instead of a "grunt"