Hi All,

I am new to the PC interfacing world so please go easy on my if I get something completely wrong..

Basic idea is to get a few bits of data into the computer, at a reasonably fast interval. ECU in the car is too old for on board diagnostics, so making software and hardware for my laptop..

Data to retreive will be RPM, Speedo (pulses from gearbox pulse generator), oil temp, oil pressure, boost level and fuel level.

Need to know the best way to get this into the computer, at a reasonable update speed (say 100-250ms), and can't be too expensive.

Suggestions are always welcome.

Thanks guys,

Tim.

 

I would use the parallel port for data acquisition. Easy to interface, program, and is fast enough for your needs.

RPM and speed sensor should give a digital output that only needs to be sampled against a time base to calculate the result. Just need to damp the signals to a level acceptable to the printer port. I would trigger them tru an opto-isolator just to be safe.

Oil Temp & pressure, fuel level and boost signals are probably analog so you would need A/D converters to read values into printer port. Suggest 8 bit resolution A/D so it matches data width of the port.

To allow you to address each item seperately, you can use something like a 3/8 or 4/16 decoder tied to some of the printer control leads to selectively activate each individual device for input reads.

Dialtone

 

RPM signals are square wave. Speedo? Mose likely.
Oil Temp, Oil Pressure.. Boost Pressure and Fuel Level

For starters, will you be using your own sensors?

Not knowing what make/model of car and sensor configuration, I can say that you will need a digital pressure sensor. Motorola makes a whole line, I have the MPX2200DP in front of me which is a dual port sensor, takes either boost/vacuum readings.

As for the interface, from my last few days of reading, I would suggest you interface all sensors with a PIC, then collect datalogging from there. It's definitely not a day's work for this..

http://www.mystrobl.de/ws/pic/tacho/bikecurrent.htm
http://homepages.picknowl.com.au/pkl...cproject1.html

these sites might give you some idea of a general direction for your project. You could simply build the PIC to take in data from the sensors, leave them in ASCII and send them via serial to the PC. From there you could use hyperterminal for raw data and then build a program to retrieve and then quantify (ie all the mathematical calculations, wheel rotation, cylinder count...) the resulting data.

 

Ok well I have to purchase my parts through Jaycar electronics in australia, so I have to make sure all the components in the diagram are available through them.

I have access to the ADC0804 A/D converter, the MAX232 RS232 driver and the 4060 CMOS 14 stage count divider oscillator.

If someone could provide a basic circuit that I could put together to read a voltage anywhere between 0 to 13.8 volt, (which I think needs a voltage divider circuit??) it would be very helpful.

Also can someone recommend any free software which I can simulate these circuits with.. I'm using crocodile clips at the moment but it doesn't have any special IC's only very basic ones.

I am only new to the A/D area and I am starting to learn more and more about various IC's as I go.

Thanks for your help so far,

Tim.

 

Well will those components work together to make a circuit??

If not I'll have to order something in through a group in Sydney.. more $$$ than its worth.

Thanks all,

Tim.

 

The obvious solution is a micro-controller, a PIC or similar, this would provide internal A2D and be capable of doing everything you need, and transfer the data to your PC via a simple serial RS232 link.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

It's just that I haven't ever used a PIC before, and I need to get this circuit working.. How hard would the programming be for something like this?

I'm also looking at getting temperatures into the computer, I suppose the PIC could do that as well??

Any ideas for a circuit??

Cheers,

Tim.

 

For a start you need to decide EXACTLY what the signals to be measured consist of - for analogue voltages you need to scale them to give a range of zero to the positive reference (which might be the 5V rail), so 0-5V. For a 0-12V voltage a simple potential divider is all that's required. If you have pulses you need to measure the width or frequency off, again you need to know what range they vary over, and process them externally (with simple potential dividers or opamps) as required.

I would suggest you start off by building designs to measure each individual reading you want, then join them all together in a single PIC.

Much of the required programing, reading analogue voltages and displaying them, or sending them via RS232, are covered in my tutorials.

Circuits for the PIC part are also covered in my tutorials, also an opamp buffer for analogue inputs is covered - using a precision 2.5V voltage reference instead of the less accurate 5V supply.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Well at this stage i'd like to get a fuel reading into the computer, I was thinking about using the joystick port somehow but I have to do a bit more research into how accurate that would be.. the axis on a joystick just varies resistance so I should be able to integrate a fuel sender uint somehow..

Any other suggestions other than PIC?? I'm trying to do this as simple as possible and I have no programming expertise at all with PICs..

Thanks all,

Tim.

 

The problem with that is the relative values, joysticks are high resistance (100's of kohms), fuel sensors are generally a great deal lower - you would need to measure yours to find out what range it covers. You could always build your own 'resistance measuring' device, using the same capacitor charging/discharging technique that the joystick port uses, and connect it to the parallel port.

Any hardware solution would be prohibitively complex and expensive, so it's really down to either the processor in your PC, or an external processor of some kind?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

If your car has an on-board computer like all newer ones, then it already has the sensors, etc. What does the ECU in your car do if it doesn't do diagnosics? Is it more than 20 years old?
You need a circuit that is able to read the computer's memory and make changes to it if you wish like car "tuners" do. I can buy a gadget at my local tire store called an OBD-2 reader that does those things.
Car fanatics' chat forums are full of circuits and programs for an interface like a Palm Pilot or laptop computer to do what you want.

 

Nah that's basically what I'm trying to implement, doing an EFI conversion on my car, ECU is not OBD-II compliant.

If it was I'd love it cause I'd be able to read all sorts of engine stats.

I'm gonna try attaching a 100k pot to the arm of the fuel gauge and see what I can accomplish.. any recommendations to stop it sparking at all? :wink: :wink:

Thanks,

Tim.