Braineack

iTrader: (62)

this is simply the find the correct bias resistance number to use in easy therm, nothing else.


car off, MAF unplugged, read the resistance in the harness.

240_to_miata

iTrader: (2)

ok ... ive read through here and it seems like the last problem to solve is the fact that the ECU wont accept a plain old signal that doesnt change.... what we really need is a constantly changing resistor to create some wave on the circuit correct?

is it possible to use a large resistor to keep the voltage low (like weve been doing) but then also add in a circuit like this .... http://www.cappels.org/dproj/simples...r_Circuit.html

im just thinking if a change in voltage is what its looking for, then we can use a capasitor that is constantly reseting. I remember in one of my intro EE (electrical engineering) classes as a freshman here at uconn we used a capasitor to vary voltage like that

Arkmage

iTrader: (3)

OBD2 is fairly nasty and can detect a lot of strange signals and determine if they are bullshit or not. I think that flasher would cause problems due to the voltage jumping rapidly then dropping off equally fast. I think the best way to do this would to build a simple digital to analog conversion circuit. We can use a PWM output that is controlled by MAP (like boost control) and use the PWM to drive an analog converter to output the appropriate voltage. The voltage doesn't have to be anywhere close to the stock MAF, it just needs to move appropriately with RPM/Load so the ecu doesn't get all pissy.

Scott: I'll try to measure that resistance for you tonight. Please PM me so I remember. I'm about to leave work and hit the gym and I tend to forget.

240_to_miata

iTrader: (2)

damn thats a good idea.... now i see why i dropped out of EE and switched to mechanical


some1 get on this.

Arkmage

iTrader: (3)

i changed from ee to me also... but retained a bit from my former life.

i'm going to mess with that sooner or later, but for now i've got other problems to deal with.

Sorry i didn't measure that, i did my taxes and went out to dinner. forgot about it till just now (already commando and in bed).

240_to_miata

iTrader: (2)

ok after some quick research i found out that the circuit i linked is esentially a basic PWM-analog signal converter. All you need to do is use the PWM signal as the input voltage to that circuit.....
http://controls.ame.nd.edu/microcont...in/node40.html

240_to_miata

iTrader: (2)

http://controls.ame.nd.edu/microcont...in/node41.html better link... we do not need a buffer part of the circuit because who cares how clean the signal is

EDIT:

does anyone know what the voltage range is on the PWM signal for boost control? ... we need 0-5 but i have a feeling its gunna be a 0-1v

AlexO35

iTrader: (7)

Anyone still interested in this one? I've got a few ideas I'd like to toss around.
--Alex

Arkmage

iTrader: (3)

share them... I haven't had time to do it yet and I'm thinking of using ebc soon, so i'm back to square one.

AlexO35

iTrader: (7)

Ok, here's the deal....

I was planning on using a PIC, feeding it a MAP and RPM signal and processing it into an imitation MAF signal. Very similar to how Joe Perez used the eManage. I PMed Joe and he recommended an analog circuit. So....

After doing a little homework, we could use a LM2917 frequency to voltage converter to give us a RPM based voltage signal. Roughly based on this schematic, we could have a 0-5v output for 0-9000rpm. Feeding the LM2917 the CKP signal.

http://members.tripod.com/~foz11/DIY...al_speedo.html

The MAP would simply be an MS MAP sensor for the 0-5v signal.

So here is where I'm stuck. I was thinking that if both signals were cut down to 0-2.5v we could simply add them together to have a load based "map" for 0-5v. This should give the ECU an accurate enough signal to keep the CEL off, but not so accurate that its cost prohibitive.

I'm used to dealing with PLCs, so this outright hardware stuff still gets me....
--Alex

Arkmage

iTrader: (3)

the whole concept of this for me is to give an accurate enough signal for all of my emissions **** to work. I think what I'll have to do is hook the MAF into the MS for a while and datalog the results of RPM&MAP vs MAF voltage. I'd prefer a small "black box" solution which has a programmable table. This would allow it to be a multi platform device incase I need it in future vehicles as well.

AlexO35

iTrader: (7)

So a PIC may be the way to go?
--Alex

jnshk

Necro-thread time!

So, from my correspondence with Noah, it seems that the OBD2 MAF uses a digital output that flips between 0-5v. If what I've read so far in this thread is correct, the signal itself doesn't have to correspond to anything, it just has to be of the general type and in the range that the ECU is expecting, right? I wonder if something similar to circuit #2 found here: http://mechdb.com/index.php/O2_sensor_simulator would work? It basically uses a 555 timer to emulate a digital signal.

I'm not familiar enough with these things to be sure, but I would think that simply changing some of the resistor values would be adequate to get a signal from 0-5v instead of 0-1v, right? You could put it on a small board inside a small project box and tuck it away somewhere in the engine bay?

Joe Perez

iTrader: (8)

While there are some sensor types (vortex, coldwire, etc) which use variances in frequency or duty cycle of an on-off signal to represent airflow, I am nearly 100% certain that every '90-'05 Miata used a sensor which outputs a (relatively) linear 5-0v or 0-5v analog signal.

jnshk

:( Well that stinks...

Max

what about 90-93???