john banks

I gather that the engine speed output from the ECU is a battery voltage square wave whose frequency shows the RPM.

I want to get this into my microcontroller. How best to reduce this to less than 5V? How about a high impedance proportional divider into a comparator input? I could use say a 750K and a 250K resistor in series between the output and ground and tap off the middle to divide by 4 and then set my comparator voltage so say 3V?

StephenDone

Hi John,

Use a resistor in series with the signal, and then a low voltage drop diode from the resistor to your 5v supply, and another to your 0v. Also connect yout uC input to this point.

The diodes prevent the voltage at the uController input from going more than the diode voltage drop above/below 5v/0v. If you use a low voltage drop diode like a BAT-85, this should do the trick.

E.g.

O +5v Supply
|
|
___
^
/_\
10k |
-------- |
Square Wave O-----| |---O-O--O uController input
-------- |
|
___
^
/_\
|
|
O Gnd

Cheers

Steve


Oh dear. The html ate my diagram. View source and put carriage returns after the <br>'s and it'll make sense. Anyone know how you use <pre></pre> tags on this bbs ?

[Edited by StephenDone - 1/25/2002 12:25:22 AM]

John Stevenson

Pesky kids.... JB, shouldn't you be trying to cure cancer or something usefull

john banks

Thanks Stephen I follow it OK.

MorayMackenzie

John,

I assume you are adding an RPM input to your boost controller board... wouldn't that allow RPM dependant boost control?

Now all you need is to add in the TPS feed and you will have a board that is more functional than certain commercial offerings (alledgedly)

Moray

john banks

Thanks Moray! I already have TPS. This will be the icing.

David_Wallis

but when are you going to make it put more fuel in so I can use it... as I dont have a prodrive ecu??

David

john banks

There is plenty of fuel on MY99/00 UK with standard ECU up to the fuel cut on most cars unless you are one of the big turbo boys. More like too much.

On the 01 PPP see the other thread - but they up the boost and rely on the original ECU's fuelling and ignition "allegedly".

[Edited by john banks - 1/25/2002 1:42:56 PM]

David_Wallis

I've got a 94uk 5dr turbo.. I presume that does have the bigger turbo..

David

john banks

Yes, although there is probably still a lot more to be had without messing with fuelling. Need an air fuel ratio meter to know along with other safety monitoring.

Cosie Convert

Dave

My 95 WRX was maintaining the fueling up to 18.5 psi then the EGT started to creep up so I've called it a day there for the moment.

You need to beware that as far as fueling is concerned it is the mass air flow meter output that is the primary (perhaps only) reference for the ECU's fuel calculation during open loop.

That means that using a MBC/EBC and controlling to a manifold pressure of 18 psi may be safe one day and not another ! This is due to the actual air flow changing due to the ambient conditions and charge temperature.

I prefer to monitor EGT rather than lamda as it gives me a better indication of engine conditions.

john banks

I shy away from EGT as it is all a bit hot and greasy! I prefer splicing wires neatly

But yes, EGT is better. Or both if you want the starship enterprise.