My new Boost/EGT Gauge - PeachParts Mercedes-Benz Forum

300SD81 · #1 07-20-2008, 11:36 PM

I've posted bits and pieces of this elsewhere, but here it is all together...

Presenting the homemade digital boost/exhaust/EGT gauge!

(Note Mercedes Star etched into circuit board)

Total cost was $10 with generous use of free samples available from almost every semiconductor company. The large chip on there is a PIC microcontroller programmed with Microchip's USB serial port library and about 300 lines of my own C code. It uses a MAX6675 0-1024C thermocouple to digital converter for EGT and 2 MPX4250GP 0-36psi pressure sensors for boost/exhaust.

The display,

(oil/transmission sensors are in the works, temperature sensor chip outputs full scale when no thermocouple is conneted)

written in C#, simply reads the serial port (raw binary ADC input from microcontroller), converts the data to PSI/degF and outputs it on the gauge.

I haven't installed it in the car yet, but will be installing the boost gauge function only first. Don't have the money for new manifold/turbo gaskets at the moment, or a tap to thread the manifold. For now its going to be read on a laptop in the passenger seat, but this is going to be mounted under the glovebox as soon as I can find a old flatscreen that can be taken apart and mounted in the drivers sun visor.

I also have parts on order for an accelerometer, which I should be able to program to give me 0-60 times fairly easily (velocity is the integral of acceleration, should be easy to calculate). I can't get the gauge design for it to look good, which is why its not shown.