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Old 03-04-2009, 10:34 PM   #41 (permalink)
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That seems like the best idea so far. How about a ACS712 bi-directional sensor. It is less than 3 bucks and can handle 2.1kV so it might also be worth looking into.

Either way it looks like a small board is going to be needed near the injector wire to make it work. So at least a 7805, capacitor, and voltage booster circuit to get the output to 5V when it is sensing current. Might not be that bad to build.

I will be ordering a bunch of stuff to build a battery balancing circuit for my car soon so I will probably get some stuff to try this out at the same time.

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Old 03-04-2009, 11:07 PM   #42 (permalink)
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Here is a more basic type:
How to measure current and power - using a hall effect transducer - clamp

It's gonna take some homework

If you are thinking a plugin solution then perhaps a separate voltage reg. So roughly speaking we are trying to turn anything above, say .5 amps into >2.5 volts. With maybe 5 amps current capability. Might be a hall effect and a mosfet. Dang, clamp on would be nice worth doing some homework for that.
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Old 03-05-2009, 09:19 AM   #43 (permalink)
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the other option that comes to mind is an opto isolator in parallel with the injector.

This one would need a little protection on the input (2v zener and at 250 ohm resistor at least),
NTE3045

w/250 ohms, it would only be at .008 amps if the injector holds at 2v. The test conditions list .01 amps so with the built in darlington it might be useable. The darlington collector emitter can handle 80 volts, so it *could* be doable with just 3 components, maybe, and a plug in. Like $3 in parts.
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Old 04-09-2009, 02:46 PM   #44 (permalink)
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I still have no perfect solution to the peak and hold injectors without cutting the injector wire. The opamp circuit works just fine and shows ok looking on the scope. It doesn't give a single pulse but a double pulse. When the voltage spikes from the inductive kick it goes high again. So the only thing I have been able to think of is maybe when coasting down with the injectors on just at 1% duty cycle or so the arduino is missing the interrupt signal and not stopping the injector open timer. I set the delay to 0 to try and take that out of the list of things that could cause problems. Didn't seem to do anything.

If missing interrupts is the case then the only choice is to cut the injector wire and put a current sensing circuit in there to trigger the arduino. The signals are pretty short on the scope. A current sensing system could trigger anytime there is current flowing so it would get rid of the problem of the inductive spike making a double pulse out of the signal.

If it is something else I am out of ideas to try I am probably just going to try building a current sensing circuit and see what that can do for me. It won't be ideal having to cut the injector wire but it at least should reliably read the signals.

For the simple circuits the pot across the zener seems to give good readings as long as the voltage is stable. The opamp gives good readings for various voltages but then goes nuts on very low duty cycle signals. If I can't do any better I think the pot across the zener gives better numbers since the voltage jumps don't seem to be that big of a deal compared to it showing 12-18gph while coasting or slowing down.
Give me some hedge trimmers and I'll cut those wires
I have been reading this thread trying to find a solution to the slight innaccuracies I am seeing.. Nothing like 18 gph but some darn weird fluctuations where it seems to prefer certain mpg sweet spots like 12 and 21. Thats not to say I cant make it read 15 or 16 mpg it just doesnt like to. On flat ground 1% tps movement OR LESS can be the difference between 13mpg and 22 mpg. Anyway keep up the good work Ill try to follow this thread to see what happens. I still think an actual flow meter would be better.
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Old 04-11-2009, 01:28 PM   #45 (permalink)
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Put a 22K resistor in for R2 in the picture and it seems to read properly now. Apparently I was only reading the very low end of the signal before because with the calibration I was using it is reporting 10gph at idle now

I will adjust the calibration now and hopefully it should be all good. I will keep the laptop showing the injector pulse width and keep track of the MPGuino for a while and make sure it is long term stable but it seems about right now.
At this point could you help me with some references because I am going to be having to do something similar. But I already know that 22k isnt going to cut it.
What size engine does this vehicle have? What is its idle gph? What is its redline no load GPH? What is its redline full load GPH?

I have been rereading this text http://www.tomco-inc.com/Tech_Tips/ttt38.pdf
And that whole peak and hold thing stinks because the signal is all over compare to the other. I take it what we are trying to do is shave the bottom and top off so we can just read the middle thats active the whole time the injectors are open.
Did you try reading the resultant signal AFTER the zener? I guess I am not sure what the zener is actually doing. Its a diode right?
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Old 04-14-2009, 01:24 AM   #46 (permalink)
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I am being a bit slow about this problem but I have not quit thinking of solutions. The best thing I can still come up with is to use a ACS712 bi-directional current sensor. That should be able to read even the inductive spikes and give a clean signal to the mpguino that will be able to remain as is with no modifications.

My plan is a small board with a 7805, bridge rectifier, ACS712, and a 741 op amp. The ACS712 will go inline with the rectfied injector wire with the 7805 powering it. The output will use the opamp to sense voltage over 2.55 or so and go high at 12V and feed that signal into the mpguino that will then cut it back to 5v and should reliably work.

Optionally instead of using a bridge rectifier to keep the output voltage of that current sensor between 2.5V and 3V a dual opamp could be used that is set as a window switch to turn on above 2.55V and below 2.45V but that would leave a little notch in the signal that would probably mean a missed interrupt like I am getting with the simple opamp circuit I tried last.

If the rectified signal works good then I say leave it just for the extra reliability. It will be needed to keep the current flowing one direction through the current sensor and make the inductive spike much smoother looking to the chip and give better readings hopefully.

I should have a few ACS712 chips here tomorrow and will try and build the circuit this week and see what I can figure out.
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Old 04-22-2009, 01:42 PM   #47 (permalink)
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Quote:
Originally Posted by dcb View Post
Here is a more basic type:
How to measure current and power -* using a hall effect transducer - clamp

It's gonna take some homework

If you are thinking a plugin solution then perhaps a separate voltage reg. So roughly speaking we are trying to turn anything above, say .5 amps into >2.5 volts. With maybe 5 amps current capability. Might be a hall effect and a mosfet. Dang, clamp on would be nice worth doing some homework for that.
I have one of those hall effect transducers but the documentation says 20 mA max supply current. I am not sure how to limit that off of a car battery supply.. I dont want to burn this thing out. How can I limit the current to 15-20 mA?
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Old 04-22-2009, 02:32 PM   #48 (permalink)
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If you hook the output up to the guino injector lead, you should not get anywhere near 20ma out of it.

I would just try putting 12 volts accross it (if it is rated for at least 12v) and connecting the output to the injector-in connecter on the guino, then wrapping the injector lead around it or around a ferrous core of some sort to amplify the signal.

Then try and scope what voltages are reaching the CPU pins.

If it works, yippie , If you get an inverted gph, then that is promising, can fix in software.

Unfortunately I have neither pulse and hold or diesels at my disposal so I have to grope around a bit in these areas.
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Old 04-22-2009, 03:09 PM   #49 (permalink)
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Quote:
Originally Posted by dcb View Post
If you hook the output up to the guino injector lead, you should not get anywhere near 20ma out of it.

I would just try putting 12 volts accross it (if it is rated for at least 12v) and connecting the output to the injector-in connecter on the guino, then wrapping the injector lead around it or around a ferrous core of some sort to amplify the signal.

Then try and scope what voltages are reaching the CPU pins.

If it works, yippie , If you get an inverted gph, then that is promising, can fix in software.

Unfortunately I have neither pulse and hold or diesels at my disposal so I have to grope around a bit in these areas.
I am not sure I understand. Here is a link to it and others. but the name in the link is the one I have. http://scienceshareware.com/articles...ent-sensor.pdf

this sensor has 3 contacts. ground, supply, and sensor output. the output will be something like 0.043 volts. Well if I remember correctly. So it will need amplified up to around 5? volts
The supply to the sensor can be 8 to 30 volts so that isnt a problem but it says max supply current is 20 mA.
the injector lead will just go through the middle of it though I am not sure if going through more then once would help amplify. regardless it will need to be amplified. Hopefully it should put out a near digital on and off signal with the right mix of electronics.
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Old 04-22-2009, 03:52 PM   #50 (permalink)
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do you have a picture of the sensor and/or part number?

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