Pressure and gas sensor, voltage problem

[mirzam]

I am planning on making a gas and pressure sensor for use in my lab.

So I got the following:
- Raspberry Pi B+
- Lots of jumper wires
- A breadboard
- Figaro TGS2600-B00 Gas Sensor: http://uk.rs-online.com/web/p/gas-detection/5389960/
- MCP3008 microchip http://www.adafruit.com/product/856
- MPXA6400A pressure sensor (20-400 kPa range): http://cache.freescale.com/files/sensor ... H6400A.pdf

So I got the microchip and gas sensor working with the 3.3 dcV supply and some Java programming, picture: http://imgur.com/DWI5N8W

I haven't been able to find a pressure sensor that was compatible with 3.3V, so I found one with 5 dcV supply requirement. The MCP3008 works fine with 5.0V supply. But I guess GPIO/MISO isn't so happy about that. Also I'm not sure if any voltage will jump into the RasPi through MOSI?

I'm planning on using a simple voltage divider: http://www.raltron.com/cust/tools/voltage_divider.asp
But I'm not sure where to put it. I guess it must be before GPIO/MISO?

The pressure sensor is very small, so I need to do some careful soldering to fit them into a stripped jumper. Any tips on the way before my clumsy fingers makes a ravage?

[mikronauts]

If you run the mcp3008 on 3.3v, the voltage divider has to go to between the analog output of the sensor, and one of the analog inputs of the mcp3008

alternately, you could run the mcp3008 at 5V, then put the voltage divider on MISO - in this case, all of the analog inputs would be 0-5V (to be more accurate, 0-X, where X is whatever the Pi's 5V is when the value is sampled)