While rebuilding my engine I thought about what additional instrumentation I wanted. I needed a few more instruments to aid in the engine system development and to insure that it's operation remained within reasonable parameters. We spend a lot of time extolling the virtues of the 928, and we know that adequate and accurate instrumentation is not one of the car's strong points. I wanted something that wouldn't intrude too much on the stock look of the interior. I wasn't too taken with the idea of adding a separate instrument panel, or a row of gauges on the "A" pillar. I wanted to keep the stock A/C control and outlets in the center console as well as the radio. I could do without the ash tray and clock.

This really limited the options, plus I was having a hard time determining exactly what parameters I wanted to measure and what type of instruments to get. I realized that some measurements would be important during development, or possibly for troubleshooting a problem, but wouldn't be necessary later. Frustration and indecision set in.

One day, I had a rare phenomenon happen. I had an idea! That idea was, "don't bother with discrete instruments". Use virtual instruments on a small computer screen. I could have all the instruments I wanted, in whatever format I wanted. I did some research and found that it was feasible to do. It ended up being not inexpensive though. Example of virtual instrument panel.

I found a 7" touch screen monitor on eBay and snagged it. It is a Lilliput brand with 800 x 480 resolution. It appears adequate for the job, but may not be bright enough in sunlight. The touch screen reduces the brightness a bit. Experience will tell on that possible shortcoming. It is about 7.5" wide, 5" tall, and 1.5" thick and it will fit in the ash tray/clock area without extreme hacking of the console. It should not be in direct sunlight often there. It would be nice to have the instruments in a more line of sight location for normal driving, but since these are an addition to the normal instruments that is probably a low priority. The 800 x 480 resolution is not common and some video adapter cards do not support it. I found a hacked version of the BIOS for my car computer which would support 800 x 480, but then found that the monitor won't accept that resolution. The closest I could get is 720 x 480. That causes about 10% horizontal non linearity. It's not noticable with DVD video and otherwise acceptable.

I needed an analog to digital converter (DAQ) to get the sensor voltage into the computer. I decided on one made by Measurement Computing, www.mccdaq.com. I chose their PMD-1208FS for about $150. It has 8 analog input channels with11 bit resolution, two analog output channels, and 16 digital in/out channels. It also has a 32 bit event counter. It will scan at a rate of 50,000 samples per second in continuous scan mode with normal software paced scan of 250 scans per second. A less expensive model (PMD-1208LS) is available for $110 with the same features except a slower maximum scan rate. In experimenting with the analog to digital converter for instrumentation use, I find that 3 scans per second is very adequate so either of these units would work fine. These DAQ's are configurable for different uses. I chose +/- 10 volt single ended input. The PMD-1208 DAQ's use the USB to interface with the computer, and two can be daisy chained together to give more I/O channels.

Next, I researched temperature sensors. The normal Bosch NTC resistive sensors we already have on the car seemed a good place to start. I found that these sensors are not at all linear. The resistance vs. temperature relationship is more logarithmic than linear and posed problems with accurately obtaining a linear temperature vs. voltage output. Also, these sensors are not very consistent and have more variation between sensors than I wanted to deal with. See a temperature vs. resistance graph I plotted for Bosch type NTC sensors.

Thermocouples are good temperature sensors which give accurate output over a wide range of temperatures. The are mechanically rugged, relatively inexpensive, and are built for a variety of applications. I found some (Type K) at MSC Industrial Supply, http://www1.mscdirect.com/CGI/NNSRBR. Look around page 4540 of their on line catalog.

The problem with thermocouples is that the output is only a few microvolts per degree and they measure the relative temperature difference between the two ends of the wire. By themselves, that isn't sufficient to drive an instrument. Amplification is required to get the output up to the voltage range needed by the DAQ, and something called cold junction compensation is needed to make the output voltage relate to absolute temperature rather than the temperature difference between the wire ends. Fortunately, Analog Devices makes a chip that does all this. It is their AD595 chip. It comes in several flavors. One is the "A" model which is accurate within +/- 3 degrees C, and the "C" model which is good to +/- 1 deg C. Naturally, I chose the more accurate AD595C. These chips are not cheap at $15 to $18 each depending on vendor and whether it is the "A" or "C" style. The benevolent Analog Devices company, http://www.analog.com/en/index.html, gives out free samples. Only two at a time though. One external resistor is all that is required to increase the gain of the chip so the thermocouple will output enough voltage to drive the DAQ. I chose 65mv per degree C along with a 10 volt supply for the AD595 to give me approximately 8 volts output to the DAQ at 125 deg C (257F). The AD595 will output a voltage to within 2 volts of it's supply so with a +10 volt supply, it's output is limited to about 8 volts max. The conversion to degrees F is done in software. I'll use 5 channels for temperature and the remaining 3 channels for pressure measurement. Any pressure transducer that will output in the range of 0 to 5 volts will work. Voltage can be fed from the 928 oil pressure sensor if desired.

I also used Measurement Computing's USB-TC DAQ unit. It has inputs for 8 thermocouples which you can connect directly without need for the Analog Devices AD595's (one per temp probe), and a separate +10V regulator. The USB-TC costs $299. The benefit of this unit is no external circuit boards to build for the AD 595's and the 10V power supply. I'll use the USB-TC for thermocouple inputs from each cylinder for exhaust gas temperature. The USB-TC also has 8 digital in/out channels in addition to the 8 thermocouple inputs.

The digital in/out channels can be used to either control external circuits or to accept a high/low input for use by the software. I have over/under limits set up to trigger software alerts or to control external circuits. These are on engine oil pressure and temp, engine coolant temp, fuel pressure and transmission oil temp. I will monitor transmission oil temp and when it exceeds a set temperature, I'll have the digital output automatically turn on the transaxle oil cooler pump. The alerts could cause an indicator on the screen to flash, or play a .wav file. Imagine a .wav file of your wife yelling, "you are going too fast, idiot", when you exceed a certain speed. The digital outputs could be used to sound a loud alarm, flash a light right in your line of sight, or even shut down the engine if you lose oil pressure. Anything is possible. The digital outputs won't source much current so an external interface is required to control anything over a few ma.

Next, I needed to decide what application development tool to use to write the software. The Measurement Computing DAQ's come with a function library to use with several software development tools. There is a function library for VB, C++, Delphi, Labview, and Softwire. Softwire only works with VB.net. I tried Softwire, but found not enough properties available for the instruments to make them look the way I wanted and there were no functions available to use the counter which I needed so I could have a tach or otherwise measure a frequency (speed). VB.net is a bloated, hard to use, pig of a development tool too although the Softwire shell is interesting. I had the same results with Labview; not enough instrument properties and no counter available. I settled on using an old version of Borland Delphi I had. Version 3. Delphi is fairly easy to use and the application compiles into a nice small .exe file. I used an Active X instrumentation component library I had from Global Majic Software, http://www.globalmajic.com/products.asp?PTID=3. I primarily used their Angular Gauge active X component since I wanted analog appearing gauges. Other display formats are available. The instruments have enough properties to make them look any way you want.

Data logging is possible with the scanned parameters from the DAQ saved to a disk file. I did not implement that since my ECU (DTA P8Pro) does data logging already.

I was intending to use a simple laptop to drive the small screen and accept the input from the DAQ. I discovered that dedicated car computers are becoming readily available and these seemed to be better suited. The main reason I chose the car computer is because they have 12 volt powered power supplies that are configured to operate with the ignition switch on the car. The computer never really shuts down. With the engine shut off, the computer goes into hibernation mode and uses very little power from the vehicle battery. When you start the engine, the computer comes out of hibernation and is operational within a few seconds. You do not need to go through a shutdown/boot up process. Win XP, or 2k could be used for an OS. Win 98 isn't recommended. Some version of Linux could be used as well except that my instrumentation application is written for 32 bit Windows, and Win XP seems more prevalent. Some sources for the car computers and related items can be found at: http://www.logicsupply.com/default.php/cPath/50, http://www.carbotpc.com/, http://www.opussolutions.com/, http://www.mini-box.com/site/index.html, http://www.epiacenter.com/. Once you have the computer in the car, all sorts of other things are relatively easy. GPS receivers are getting really cheap now, and of course music storage is only limited by hard drive space. DVD's can be played as well. The car computers can be fitted with nearly all the external devices usually used with laptops or desktops. They usually have a 120 vac power supply available for use in the house, and internet connection can be accomplished through wireless links to your home LAN and ISP. Wireless connections for mice, keyboards, and a host of other things can be fitted too.

I have the car computer built and it has all the features I need for present and future needs I can think of. It has a CD/DVD reader, wireless connection to my home LAN/ISP for file transfer, Bluetooth communications, wireless mouse and keyboard for easier programming of my DTA ECU (normally, the touch screen precludes the need for a mouse and a virtual keyboard can be called up if required), 4 USB ports, 2 comm ports, Compact Flash, and other memory card formats. It's not in the car. I plan on the computer fitting in the space that is now occupied by the rear seats. Those will be removed and the space converted to storage and component mounting - car computer, stereo, electric power steering pump, electric vacuum pump. I'm still working on final software development and my car isn't ready to go yet.