Small Engine ECU, EFI Moped Using An Audrino UNO

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01-26-2012
Sean Armstrong

Small Engine ECU, EFI Moped Using An Audrino UNO

After some days of thinking about electronic fuel injection for a moped, ive decided to take it on. Parts come up to $80, and the rest is programming. I have never before programmed in c, c++, java, nothing! I'm quick to adapt and learn, might make some rookie mistakes but heres what I have so far. I'm programming for an Audrino UNO Board so really limited program space, but definitely doable at 300,000 cps hardware wise. ( I know spacing is atrocious but I've only been learning for 8 hours now, lol)

So Heres the question: I do not know where to begin with the loop program, I need pin6 to fire after every other highlow reading on A0. on top of that, simultaniously, i have to monitor pin A2 for a integer optimal reading of around 65 (each integer from the A/D converter is = to 4.9milli volts) int range of the A/D converter is 0-1023. if the reading is not 65, then the engine is running too lean or too rich. should i use an "if do" statement, and how would I have the program adjust the pulse width (on/off time) of the fuel injector to the right amount? would i have to make a int table, and do a little R/D as to how long with an int reading of 65 on pin A2 the solenoid opens? I don't even know what i should startoff with. below is the boot up to prep and start the engine with everything warmed up and primed

Code:

/*Goal is to manage the fuel system of a small displacement gasoline engine using an open loop system, only anaylzing the exhaust gases through an O2 sensor. The object is to have Audrino anaylze the voltage readings of the O2 sensor and adjust the pulse width of the fuel injector to control the amount of fuel entering the engine. Audrino has to be self correcting, and quick to adapt to different engine displacements of a small range. The timing mechanism will be an analog magnetic pickup coil. The injector needs to fire every other pass of the magnet on the flywheel Pin labels 3=O2 Sensor Heater 4=Ready to fire LED 5=fuel pump 6=fuel injector solenoid 7=starter solenoid 8=warning LED, engine not ready A0=RPM sensor 9=O2 sensor input */ void setup() { digitalWrite(3,HIGH); //Turns O2 Sensor Heater On while(3,HIGH){digitalWrite(8,HIGH);delay(1000);digitalWrite(8,LOW);delay(1000);} digitalWrite(5,HIGH); //Activates Fuel Pump delay(3000); digitalWrite(6,HIGH); //Fuel injector primes engine delay(500); digitalWrite(6,LOW); delay(10500); //delay for the 02 sensor to finish warming up digitalWrite(3,LOW); digitalWrite(4,HIGH); //Indicates Engine is ready to fire digitalWrite(7,HIGH); //turns engine over delay(5000); digitalWrite(7,LOW); //Kills Starter solenoid analogRead(0); //sets A0 to read engine RPMS analogRead(9); //reads o2 sensor voltage level } void loop() { }
01-26-2012
quzah

Quote:

Originally Posted by Sean Armstrong

So Heres the question: I do not know where to begin with the loop program, I need pin6 to fire after every other highlow reading on A0. on top of that, simultaniously, i have to monitor pin A2 for a integer optimal reading of around 65 (each integer from the A/D converter is = to 4.9milli volts) int range of the A/D converter is 0-1023. if the reading is not 65, then the engine is running too lean or too rich. should i use an "if do" statement, and how would I have the program adjust the pulse width (on/off time) of the fuel injector to the right amount? would i have to make a int table, and do a little R/D as to how long with an int reading of 65 on pin A2 the solenoid opens? I don't even know what i should startoff with. below is the boot up to prep and start the engine with everything warmed up and primed

First you need the basic structure of your program. I like to do that with words first, before programming begins:

Code:

initialize engine while i want to keep running do a reading if it's time for an A2 do something if it's too rich or too poor otherwise if it's not time for an A2 do whatever it is you do

Just something like that, to get an idea of how it's actually supposed to work. (Normally I'd try to write out a full working description of what I want to do, but you've basically done that.) The above is basically the pseudocode step. It's not really code, but it resembles it roughly, so I can get an idea if it looks good.

Code:

int main( void ) { setup(); /* have setup defined some place */ while( some_condition ) { readpins(); handlepins(); } return 0; }

Now of course you may need to return some appropriate values from those functions, or pass them arguments, or what have you, but that's a general idea of how I'd work it out.

Quzah.
01-26-2012
anduril462
Awesome project! You say moped, which I imagine as a bicycle with a small motor. Do they come with electric starters now or do you mean a scooter, like a little Vespa or something? Is there a throttle and throttle body, or just a "dumb" air intake with no speed/power control? The ECUs would be wildly different. A few general notes:
- Sensors aren't always linear. Look at the specs for the O2 sensor and make sure you properly adjust for readings that are farther away from your ideal reading of 65. If it's non-linear, a lookup table with some simple interpolation would be good here.
- Look at your injector, fuel pump specs and throttle body specs. You will need to know the pressure of your fuel pump, the open and close time of the injector and it's flow rate at that pressure to figure out how much fuel you're getting.
- You will need to know the flow rate of your throttle body or intake manifold or whatever to know how much air you're getting.
- You want a ratio of a little more than 14:1 air:fuel (by mass, not volume or whatever).
- I've never used a analog mag pickup, at least not one that spits out engine speed. I'm used to something like a missing tooth on the flywheel that makes a pulse in the mag pickup. If that's how your pickup works, you probably need to digitize that signal and tie it into one of the interrupt pins on your board. I'm no electrical engineer, but a high pass filter, a Schmitt trigger and a few resistors to get you in to the right logic levels would probably be enough for your moped.
- Some of the delays in your setup function seem way too long, particularly the fuel pump, and the starter, and maybe the O2 sensor. I'm not familiar with whatever moped/engine you have, and I don't know what sensors, etc you have, but it just seems long to me.
01-26-2012
itCbitC

Quote:

Originally Posted by Sean Armstrong

...
So Heres the question: I do not know where to begin with the loop program, I need pin6 to fire after every other highlow reading on A0. on top of that, simultaniously, i have to monitor pin A2 for a integer optimal reading of around 65 (each integer from the A/D converter is = to 4.9milli volts) int range of the A/D converter is 0-1023.

What kind of micro are you using for doing this and can you post a schematic?

Quote:

Originally Posted by Sean Armstrong

if the reading is not 65, then the engine is running too lean or too rich. should i use an "if do" statement, and how would I have the program adjust the pulse width (on/off time) of the fuel injector to the right amount? would i have to make a int table, and do a little R/D as to how long with an int reading of 65 on pin A2 the solenoid opens? I don't even know what i should startoff with. below is the boot up to prep and start the engine with everything warmed up and primed

How about an interrupt service routine (ISR) which is executed everytime reading == 65?
01-26-2012
Sean Armstrong

Quote:

Originally Posted by quzah

First you need the basic structure of your program. I like to do that with words first, before programming begins:

Code:

initialize engine while i want to keep running do a reading if it's time for an A2 do something if it's too rich or too poor otherwise if it's not time for an A2 do whatever it is you do

Just something like that, to get an idea of how it's actually supposed to work. (Normally I'd try to write out a full working description of what I want to do, but you've basically done that.) The above is basically the pseudocode step. It's not really code, but it resembles it roughly, so I can get an idea if it looks good.

Code:

int main( void ) { setup(); /* have setup defined some place */ while( some_condition ) { readpins(); handlepins(); } return 0; }

Now of course you may need to return some appropriate values from those functions, or pass them arguments, or what have you, but that's a general idea of how I'd work it out.

Quzah.

Okay, basically i need something that works like this:

Code:

void loop() { if{A2=int65}; (keep pulse width on pin6 the same) else{A2<65} (increase pulse length on pin6) else if{A2>65} (decrease pulse length on pin6) }

im not familiar on how to define an input as an integer, get the program to take in the integer number, and depending on the reading, change how much longer or shorter the fuel injector needs to pulse, plus how to get the program to take in the adjusted number and only make the injector fire every other rotation
01-26-2012
Sean Armstrong
Quote:

Originally Posted by anduril462

Awesome project! You say moped, which I imagine as a bicycle with a small motor. Do they come with electric starters now or do you mean a scooter, like a little Vespa or something? Is there a throttle and throttle body, or just a "dumb" air intake with no speed/power control? The ECUs would be wildly different. A few general notes:

Sensors aren't always linear. Look at the specs for the O2 sensor and make sure you properly adjust for readings that are farther away from your ideal reading of 65. If it's non-linear, a lookup table with some simple interpolation would be good here.
Look at your injector, fuel pump specs and throttle body specs. You will need to know the pressure of your fuel pump, the open and close time of the injector and it's flow rate at that pressure to figure out how much fuel you're getting.
You will need to know the flow rate of your throttle body or intake manifold or whatever to know how much air you're getting.
You want a ratio of a little more than 14:1 air:fuel (by mass, not volume or whatever).
I've never used a analog mag pickup, at least not one that spits out engine speed. I'm used to something like a missing tooth on the flywheel that makes a pulse in the mag pickup. If that's how your pickup works, you probably need to digitize that signal and tie it into one of the interrupt pins on your board. I'm no electrical engineer, but a high pass filter, a Schmitt trigger and a few resistors to get you in to the right logic levels would probably be enough for your moped.
Some of the delays in your setup function seem way too long, particularly the fuel pump, and the starter, and maybe the O2 sensor. I'm not familiar with whatever moped/engine you have, and I don't know what sensors, etc you have, but it just seems long to me.

Its more like a vespa, just modernized. the newer scooter/mopeds have a vaccum advance carbuereator, electronically controlled ignition via a CDI box, which measures pulses off the magnetic pickup coil, kindof the opposite of what your used to, with a hall effect sensor. Then sends a charge from a capacitor to a step up coil to make the spark plug "spark".
Im working on prototyping a new intake system, which would roughly be a metal tube with a butterfly valve controlling air flow, and the fuel injector attached right next to the head, psudo throttle body. The specs from delphi say an ideal reading would be around 320mv, which is a slightly more rich reading of say around 14.5:1. a lower voltage means too rich, and a higher voltage would mean too lean. the board converts analog signals to digital signals as long as you define the input as an integer, each single integer would mean a defference of 4.9mv from the last one. so an int of 65 from pin A2 would be close to 320mv, and a reading of 66 would mean a reading of 324.9 ect ect. im hoping to not have to monitor the intake vaccumm or mass by only monitoring the output of the engine to change what goes in. the whole fuel pump delays aand all are just to build pressure of around 30psi for the injector to work properly. the rest of the delay is for the O2 sesor to heat itself up completely to give an accurate reading once the engine starts to turn over. Logic voltages on the board are 0v for low, 5v for high. the analog converter will digitize the 1.3v reading of the mag pickup to 5v. anytime the magnet on the flywheel isnt passing beneath the coil, there is no voltage reading. Theoretically it should work, i think....
01-26-2012
Sean Armstrong

Quote:

Originally Posted by itCbitC

What kind of micro are you using for doing this and can you post a schematic?

How about an interrupt service routine (ISR) which is executed everytime reading == 65?

Never heard of an ISR, how does that work?
do you need a schematic of the "ECU" board, or the whole system setup? I have both
01-27-2012
itCbitC

Quote:

Originally Posted by Sean Armstrong

Never heard of an ISR, how does that work?

Well you can read about 'em here!

Quote:

Originally Posted by Sean Armstrong

do you need a schematic of the "ECU" board, or the whole system setup? I have both

Yep! it'd be nice if you could post both the schematics. Never worked with an Audrino UNO board, so not sure what micro or compiler it uses.
01-27-2012
quzah

Quote:

Originally Posted by Sean Armstrong

Okay, basically i need something that works like this:

Code:

void loop() { if{A2=int65}; (keep pulse width on pin6 the same) else{A2<65} (increase pulse length on pin6) else if{A2>65} (decrease pulse length on pin6) }

im not familiar on how to define an input as an integer, get the program to take in the integer number, and depending on the reading, change how much longer or shorter the fuel injector needs to pulse, plus how to get the program to take in the adjusted number and only make the injector fire every other rotation

Well basically you should have some way to get values from whatever you are reading. Just like you are able to send values. Looking at your first post:

Code:

analogRead(0); //sets A0 to read engine RPMS analogRead(9); //reads o2 sensor voltage level

Those read apparently, so I'm assuming then that there is a variable already declared some place, that ends up getting the result of that. You just need to find out what it's called, and compare it to whatever you expect.

Code:

void loop( void ) { int everyother = 0; while( 1 ) { if( everyother ) { analogRead( SOMEPIN ); if( WHATEVER < 65 ) /* to use a constant integer value, just put the value like so */ increase( PIN6 ); /* however you do that, and according to whatever formula you have */ else if( WHATEVER > 65 ) decrease( PIN6 ); /* as per above */ /* else it is 65, so don't do anything */ } everyother = ! everyother; /* flip this from 0 to 1 or 1 to 0 */ /* do you need a delay here? */ } }

Basically you're looking at something like this. WHATEVER is whatever you have that stores the values you've just read from your analogRead.

Quzah.
01-27-2012
anduril462

Sorry, this turned out to be quite a long-winded reply!

Quote:

Originally Posted by Sean Armstrong

Its more like a vespa, just modernized. the newer scooter/mopeds have a vaccum advance carbuereator, electronically controlled ignition via a CDI box, which measures pulses off the magnetic pickup coil, kindof the opposite of what your used to, with a hall effect sensor. Then sends a charge from a capacitor to a step up coil to make the spark plug "spark". Im working on prototyping a new intake system, which would roughly be a metal tube with a butterfly valve controlling air flow, and the fuel injector attached right next to the head, psudo throttle body. The specs from delphi say an ideal reading would be around 320mv, which is a slightly more rich reading of say around 14.5:1. a lower voltage means too rich, and a higher voltage would mean too lean. the board converts analog signals to digital signals as long as you define the input as an integer, each single integer would mean a defference of 4.9mv from the last one. so an int of 65 from pin A2 would be close to 320mv, and a reading of 66 would mean a reading of 324.9 ect ect. im hoping to not have to monitor the intake vaccumm or mass by only monitoring the output of the engine to change what goes in. the whole fuel pump delays aand all are just to build pressure of around 30psi for the injector to work properly. the rest of the delay is for the O2 sesor to heat itself up completely to give an accurate reading once the engine starts to turn over. Logic voltages on the board are 0v for low, 5v for high. the analog converter will digitize the 1.3v reading of the mag pickup to 5v. anytime the magnet on the flywheel isnt passing beneath the coil, there is no voltage reading. Theoretically it should work, i think....

You can control the engine solely from the O2 sensor, but it's not going to work very well. The O2 sensor just isn't responsive enough, and it's happening after the fact. It will work well enough in steady state, like idling or cruising with the throttle at a fairly constant position. As soon as you open or close the throttle much, or go up or down hill, your control system will start to break down. You need some "before the fact" controls. The O2 sensor should be used in addition to your main control system, which is currently the carburator. The carb that's on there now adjusts the fuel rate based on your throttle position through metering rods and complicated little fluid tunnels, and it probably has an accelerator pump that dumps extra fuel in there when you crank the throttle hard to accelerate quickly. Your throttle body and EFI system should try to replicate this.

I would say the bare minimum for a good control system would be throttle position, air flow and O2, though air flow may not be practical in your little scooter. Your main control loop adjusts fuel rate based on the air intake and throttle position. The O2 sensor is used to trim that up or down depending on how rich/lean you're running. The throttle position sensor (TPS) is also used to detect large changes in throttle position, for quick acceleration or returning to idle. If you go from idle to wide-open throttle, you need to open the injectors extra long to simulate the accelerator pump, or as you let the engine spin down naturally, you only need the bare minimum of fuel. You could hook up a simple potentiometer to your butterfly valve and tie that into one of your analog inputs as a crude TPS. Most fancier ECUs use two sensors for measuring air intake, manifold absolute pressure (MAP) and manifold air flow (MAF). I think both sensors are always used, but under different conditions you rely on one more than the other. IIRC, the MAP is used more for idle and low speeds when air isn't being forced into the throttle body by the movement of the vehicle. The MAF is relied on more at higher speeds, though the MAP is still used as it helps correct for altitude and ambient temperature, which affect the density of the air. I think they're fairly expensive, and will probably be tough to fit onto your custom throttle body. You could possibly just take some air flow measurements for your throttle body based on how open the butterfly valve is, and take your best guess at air flow based on the TPS. You can keep the previous reading and the current reading of the TPS to detect how big the change was, in case you need to inject extra fuel.

The sensor on the flywheel (crank position sensor, CPS) sounds like what I'm used to, a simple Hall effect sensor. I misunderstood your initial post, and thought you had some sensor that gave a varying analog reading that corresponded to engine speed, e.g. 0V = 0RPM, 3V = 4500RPM, etc. Whether a missing tooth or a magnet, it's all about the same. The CPS generates a pulse (or lack of pulse) that at a fixed point in the engine's rotation, and is usually expressed as being some number of degrees before/after top-dead-center (TDC). The engine specs should tell you in degrees from TDC when each cylinder is on which part of the combustion cycle, so you know when to inject fuel (in direct-port or multi-port injection) and when to fire the spark plugs. The CDI box does exactly that for the spark. Lucky for you, since you're doing throttle body injection, you don't really have to worry about timing your injector. In fact, many of the first fuel injection systems on cars were throttle body injectors that constantly sprayed fuel, varying the pressure or flow rate to the injector based on the air intake amount. There was no timing involved. You can if you want, however, only open the injector when the cylinder is on it's intake stroke, or probably just before. This would require a bit more tuning, but would probably result in better fuel efficiency and possibly tighter control of the fuel/air mixture meaning better efficiency. That should be good for a 1 cylinder engine, but I'm not sure how practical this is if you have 2 cylinders. Putting this on an analog input or A/D converter is probably not the best way to get your pulse though. That signal has to be converted to a digital value, which is much slower than running it through some logic gates, and you'll have to do more work at the code level to read the analog signal and make sure it's a large enough value to constitute a pulse, and not just noise you're detecting. Besides, I'm not sure if the Uno will let you trigger an interrupt on an analog signal.

As for the delays, right now, from the moment you start your scooter to the time it's ready to go, you have to wait nearly 20 seconds, which is a really long time. Half of that is the O2 sensor warming up. I would turn it on and record the current time as reported by the millis() function, and have something in your main loop periodically check the millis() function and if >= start_time+10500, and turn off the O2 sensor heater there. I might not even bother warming the thing up until the engine is running. That also goes along with not using the O2 sensor as your only or primary source of control. You probably don't need to wait 3 seconds for the fuel pump to build pressure. I think half a second there would be good. Also, don't just crank the engine for 5 seconds. Turn on the crank and grab the millis() reading. Then keep polling in a loop and if you detect the engine starts up (perhaps by checking the CPS), or you've been cranking for 5 seconds, stop the starter. Repeat 3 or 4 times, and if you don't get an engine start, then give up, you'll kill the battery and starter motor otherwise.

You probably want the bare minimum in your setup() function, like configuring the A/D converters, which pins are inputs and output, etc, and save all the actual ECU logic for a big state machine in your main loop. Here's the rough approach I might take:

Code:

void setup() { set A/D converter and GPIO mode = pre_start } void loop() { curr_time = millis() read sensors switch (mode) case pre_start: crank_count = 0 enable fuel pump delay 500ms mode = try_crank case try_crank: open injector enable starter crank_stop_time = millis() + 5000 // try to crank for 5s crank_count++ mode = continue_crank case continue_crank if engine_speed > 500 // some number significantly faster than the speed the starter cranks at // engine started, it's spinning at idle speed disable starter enable O2 heater o2_heater_enabled = true o2_heater_stop_time = millis() + 10500 mode = engine running else if curr_time >= crank_stop_time close injector disable starter crank_stop_time = millis() + 5000 // give the starter a 5s break from cranking mode = pause_crank // else, we just stay in this mode and come back here // to check if we started up or not case pause_crank: if crank_count > 5 can't start engine, bail out else if curr_time >= crank_stop_time // break's over, back to work mode = try_crank case engine_running: if (o2_heater_enabled && curr_time >= o2_heater_stop_time) disable heater o2_heater_enabled = false // here is where your control code goes case error: stop fuel pump close injector disable O2 heater disable starter // just stay here until the system is reset somehow }
01-27-2012
Sean Armstrong

1 Attachment(s)

Quote:

Originally Posted by itCbitC

Well you can read about 'em here!

Yep! it'd be nice if you could post both the schematics. Never worked with an Audrino UNO board, so not sure what micro or compiler it uses.

Heres the arduino development page:
Arduino - HomePage

Heres the board schematic
http://arduino.cc/en/uploads/Main/Ar...-schematic.pdf

Heres a distributors site with the board i have in mind
Arduino Uno - R3 - SparkFun Electronics

Heres a compiler with debugging built in, very nice. Made specifically for programming arduino
Arduino - Software

Below is the way I'm hooking up all sensors and such
I've made some modifications to the original plan, But im sticking to these ones for sure
Attachment 11399
01-27-2012
anduril462

Does the potentiometer represent the O2 sensor and the inductor represent the solenoid in the injector? What about the fuel pump, starter solenoid, O2 sensor heater and mag pickup?

It looks like your LEDs are wired backwards. The cathode (the side with the bar at the tip of the triangle) should be connected to ground. Think of it like an arrow in the direction the current goes (from + to -). Flip them and insert a current limiting resistor in series with each one, between the IO pin and the LED. Google "LED current limiting resistor" to read up on why you need them and find links that will calculate the resistor you need.

Double check that the Uno can source enough current to open/close the fuel solenoid, you may need to use a power FET to supply enough current.

Could we get some more info on the scooter and other parts, manufacturer and model number or some such?
01-28-2012
Epy

Hi, I'm only really skimming your thread but I can tell this will be very relevant:
» Pin I/O performance JeeLabs
digitalRead(), digitalWrite(), etc. are very slow, it's much faster to use bitRead() and bitWrite()

Edit: You might also consider using a different, faster device:
http://leaflabs.com/devices/maple/
Some MIT grads basically copied the Arduino and replaced the slow, primitive Atmel chip with a 32-bit ARM chip with a much higher clock speed (72 MHz vs. 16 MHz). It uses the Wiring language as well.
01-30-2012
Sean Armstrong

1 Attachment(s)

Quote:

Originally Posted by anduril462

Does the potentiometer represent the O2 sensor and the inductor represent the solenoid in the injector? What about the fuel pump, starter solenoid, O2 sensor heater and mag pickup?

It looks like your LEDs are wired backwards. The cathode (the side with the bar at the tip of the triangle) should be connected to ground. Think of it like an arrow in the direction the current goes (from + to -). Flip them and insert a current limiting resistor in series with each one, between the IO pin and the LED. Google "LED current limiting resistor" to read up on why you need them and find links that will calculate the resistor you need.

Double check that the Uno can source enough current to open/close the fuel solenoid, you may need to use a power FET to supply enough current.

Could we get some more info on the scooter and other parts, manufacturer and model number or some such?

Yes, the potentiometer represents the 02 sensor, figured using the program that I am, a potentiometer would be the closest electrical component, and the inductor represents the fuel injector. lol, I kindof threw together the whole diagram in 5 minutes, wasnt paying too much attention to polarity or anything. If the UNO board doesnt supply enough power, i was planning on using a tipi relay, or thats what someone else told me would work. As far as model numbers, pretty much its the most common engine in the world. Its a honda clone 139QMB engine, used on typically every model currently made. lookup VIP moped or Sunny moped, and thats what they look like. Ive posted a wiring diagram to help you get a better view of the whole electrical system on the moped. Ive changed my mind on having the computer work the whole moped as far as starting it and all automatically. I am just going to have a blinking yellow LED come on for fourteen seconds, and have the program turn off the yellow led and have a green one turn on solid after the 02 sensor sets itself up. Sorry I havent posted in a few days been away from the computer (probably for good measure, this whole project had me distracted at work looking a one of our bikes while i was on the clock, testing different components for output and all when I shouldve been repairing the thing, lol)

Im going to make a separate post with the whole complete wiring diagram the way it should be shortlyAttachment 11406
01-30-2012
Sean Armstrong

Quote:

Originally Posted by Epy

Hi, I'm only really skimming your thread but I can tell this will be very relevant:
» Pin I/O performance JeeLabs
digitalRead(), digitalWrite(), etc. are very slow, it's much faster to use bitRead() and bitWrite()

Edit: You might also consider using a different, faster device:
leaflabs.com
Some MIT grads basically copied the Arduino and replaced the slow, primitive Atmel chip with a 32-bit ARM chip with a much higher clock speed (72 MHz vs. 16 MHz). It uses the Wiring language as well.

Had no idea they had another open source board like audrino out there!!!Ive been looking into the board you just sent me, hopefully the compiler is decent and all. Good lookin man, definitely a hell of a lot more powerful the the uno board
01-30-2012
Sean Armstrong

1 Attachment(s)

Attachment 11407
The switch represents the Mag pickup, inductor represents solenoid, rewired the LEDS and put a resistor in line(not sure if its the correct ohms, but thats for later), potentiometer represents o2 sensor, one of the leds is supposed to be yellow, one green. not both red.
01-30-2012
Sean Armstrong

The only issue with making the system closed loop, meaning measuring the intake air vaccumm, and the total mass, is trying to find a part that will work. automakers send their specs to companies like delphi, and they work around what the manufacturer wants from the product. So i get to pick and choose from all these parts that no one has specs for, and cant program for them because i have nothing to go one, delphi has been working with me, they got interested in the project, and are sending me a few things free of charge. They are sending me an 02 sensor from their generic small engine component lines, a small fuel pump, and an 80g injector. they told me to do anymore than going off the 02 sensor, i would have to hire them on and bring them a sample bike, and they would go about designing the whole thing for me, but thats big $$$, like 5 digits. Although it would get done right, they said they could design a whole plug and play wiring harness, new fuel level sensor and pump unit to replace the in tank float on a stick, a whole custom designed throttle body with MAF, MAP, Fuel Injector, and TPS units in place. That would be the way to go completely, but I don't have the kind of money for that. I'm trying to do it for under $200, and make it affordable for customers to have their mopeds converted. #1 cause of engine failure on a moped/scooter is temperature failure. Usually cause by infrequent oil changes, or using the incorrect type of oil. Too much friction, toom much heat, premature wearing bc of metal on metal contact. The newer mopeds rolling of the line since 2011 have a 60cc engine, instead of a 50cc. They use the same jet setup as the 50cc scoots, making them run lean off the factory floor. misfiring and too high temps have me rebuilding the engines 5,10,15 times a week. I'm hoping to better the moped world with this, lol. (unfortunately I found out the new 2012 yamaha scoots are using fuel injection, so it wont be a first in moped history, but considering the price of that scooter, I have a feeling I wont be seeing those on the streets anytime soon, lol)
02-08-2012
anduril462

Sorry it took me a while to get back to you. I actually wrote this a while ago, but I was having issues with posting long replies on the forum. Any new updates? Here's my one-week-late reply.

That's awesome you're getting Delphi to work with you, and that you got all that free stuff. You could see if they have an off-the-shelf airflow sensor you could use, or at least get a part number and order it from a distributor. If you want, you can look at your local auto parts store (AutoZone or whatever) or online at a place like Jeg's or Summit Racing for an airflow sensor or hit up your local junkyard. Probably something off a small Japanese/Korean car, or any economy car would be closest to what you want. Or, if you can find a place that does go-karts and the like, they might be able to help you. There are other companies besides Delphi, too. They may contract out to Delphi, but they might have off-the-shelf choices that would work. Bosch comes to mind, and checking AutoZone's website for a Honda Civic, Cardone and Duralast have MAF sensors available for $60-80, a bit high, but you might be able to stay under $200 or close to it. I looked up specs for Yamaha scooters on their website. Looks like their low-end Zuma 50 is fuel injected now. This site suggests Yamaha has been making some EFI scooters since 2006. Should definitely be able to get your hands on a MAF sensor for one of them. Try contacting Yahama like you did Delphi or looking at a scooter/motorcycle parts store for a replacement MAF for that scooter.

I know I'm pushing the airflow sensor pretty hard, but I honestly think you wont get very good results with just the O2 sensor. And like I said earlier, you can make your own TPS for a few bucks or so, which would go a long way to helping your ECU. A simple potentiometer mounted on the shaft of your butterfly valve and tied to one of the analog inputs is all you need. Whether you need airflow or TPS boils down to this: what is the response time of your O2 sensor? Can it respond quick enough to changes in the fuel/air mixture? Response times aren't necessarily a fixed number, so it may respond quickly enough for small changes in the fuel/air ratio. If the change is huge (quick acceleration, hills, etc), the response time of the O2 sensor may be too slow, perhaps enough for the engine to stall before the mixture can adjust. I'm going to leave the issue alone after this, but do keep it in mind, I think you have lots of cheap and/or free possibilities for MAP/MAF and TPS sensors.

As for your control system, you actually have a closed loop (feedback) system, even with just the O2 sensor. Closed loop means you measure the output (how much it differs from ideal) and use that to help adjust your input. You measure the output of the combustion via the O2 sensor, and use that feedback to control the fuel/air mixture. Open loop would be to only use something like the air flow sensor or throttle to control the mixture and not look at the combustion output to see how your mixture is doing. Closed loop does not implicitly mean it's better however.

On to your schematic, your LED resistors look like they're off by a factor of 10 or so. A quick bit of Ohm's law: V=IR, thus R = V/I. Red LEDs (as an example), typically have a voltage drop of about 2.2V across them, meaning you have 5V-2.2V = 2.8V drop across your resistor. IIRC, your basic LEDs draw (very roughly) around 100mA or .1A. That means for your resistor, you have R = V/I = 2.8V / .1A = 28ohms. I don't think they make 28ohm resistors, but I think you can find 33ohm resistors pretty easily. You need the right power rating too. For that, you use P=IV, so P = .1A (2.8V) = .28W. That's just over 1/4 W, so get a 1/2W rated resistor to be safe. Note, the color, size and brightness of the LEDs will change the resistor you need. Check the specs of the LED you get and redo the calcs I just did plugging in appropriate values. A bigger resistor will result in lower current and thus lower brightness, so bear that in mind and tweak accordingly.

Looking at the page for the Uno, it looks like you can only have external interrupts on digital pins 2 and 3, meaning you can't put the mag pickup on the analog pin. I also don't see any way to make an interrupt trigger on an analog input value/range/threshold. If you're looking for something to trigger on a rise or fall of a voltage (the pulse from the mag pickup saying it completed a revolution), you should use a digitize the signal to get a clean transition, and send it to a digital input. The interrupt features in the Uno are designed to work this way. It's also not safe to simply poll the analog input for a reading and hope you catch it in that brief moment that the mag pickup has a value that is non-zero since you may end up only checking between pulses and miss data. The maple that Epy suggested says you can run an interrupt off any input, including analog, but if it's like the Arduino, it probably means you have to set the analog input to behave like a digital, in which case, you can just put it on a digital pin since you have enough of those lying around.