USB Signal Generator/ injector controller

[Dangerstevie]

Hi guys, after reading through a lot of useful info on here i decided to sign up to ask for some advice etc on my current project.
First off i know little about electronics but i am a very competent mechanical engineer and i specialised in building the ECU for our race car in uni. So i am no stranger to in depth electronics, i just don't understand them completely.

My project is to build a fuel injector test rig, allowing me to measure the flow through automotive fuel injectors.
My current design uses a 555 timer to generate a square wave signal with an amplitude of 12v and an adjustable frequency. to effectively vary the pulse width of the injectors to simulate different driving conditions so i can monitor and analyze the injector spray patterns at different RPM's.

However i quite fancy being able to digitally generate this signal and analyse the data graphically. I have NI Labview 8, and i have been told i would be able to hook up a USB interface with Labview to output the signal from the PC and hook it up to the injectors. Then by the use of a webcam i could monitor the flow through each injector into a graduated measuring cylinder and get labview to analyse and compare the flow of different injectors graphically on the computer.

Does this seem feasible to any of you guys? i think it would be a really cool project for me to do and would be a great help in any engine fuel injection development i wanted to do with my race bikes etc.

Cheers

 

[DirtyLude]

Damn, labview looks neat. Is there any documentation other than the webcasts they have, because you need to fill in a big form just to view the webcasts?

It mentions talking to 'any sensor' and a whole lot of stuff over USB. I have no idea how it does that, though, and without some documentation I wouldn't be able to suggest anything. It sounds proprietary though, and I'm guessing they sell an adapter or something.

Do you already have a sensor that measures flow, or do you need a variable injector driver and a flow sensor to talk back to labview?

Are you implementing a peak-and-hold driver, or just running these injectors saturated?

 

[Dangerstevie]

i have no idea at all about any of the labview stuff. The injectors are saturated and will use a flyback board to cope with any current spikes. I planned to use part of the Megasquirt ECU design to control the injectors, and instead of the injector control circuit receiving its signal from the processor on the ECU it would receive it from LabView.
What kind of documentation would you need? is there anything i could send you from the version of labview i have?

 

[Dangerstevie]

I have been reading a lot of labview stuff and playing with the program and i have decided its not going to be feasible at the moment to use labview to supply a signal to control injectors. So my next question.... Does anyone know of a circuit that will produce a 12v square wave pulse that will be able to trigger fuel injectors without damaging them? i will be wanting to drive 6 injectors at a time.

 

[3v0]

Grab one of you team members who can program and have them create a microcontroller program to generate the pulses. Use a single copy of the same circuit you intend to use on the car but trigger it with the microcontroller.

If the guy who does the programming is talented you can control the microcontroller via USB if that is useful.

3v0

 

[Dangerstevie]

I have no team members, this is solely a project for myself to do at home when i am bored. i.e most weeknights

 

[3v0]

Do you have any programming experiance ?

 

[Dangerstevie]

i have done no programming

 

[3v0]

I have no idea if this is a route you would like to take.

Microchip is selling the PICkit2 programmer for $34
GETTING STARTED PROGRAMMERS - microchipDIRECT

It and and a $5 processor chip is all you need to generate any duty cycle and frequency you want (5V not 12V). The code to do this is simple.

If you would like give a few more details on what you want the code to do and I/we can code it and see if you like what we are doing. If so buy the PICkit and program the chip.

Along the way you may even learn a bit about programming.

3v0

 

[Dangerstevie]

That seems like a very simple solution to my problem. I need be driving 5 fuel injectors (max) simultaneously, the max current should be no more than 7.5A (thats taking into account a doubling in A for any current spikes too). The output voltage must be 12V and to effectively simulate use on a car or bike the frequency needs to be at least 96hz (6000rpm).

 

[Mikebits]

The PICKit3 in now out.
**broken link removed**

 

[3v0]

The injectors are saturated and will use a flyback board to cope with any current spikes. I planned to use part of the Megasquirt ECU design to control the injectors, and instead of the injector control circuit receiving its signal from the processor on the ECU it would receive it from LabView.

The microcontroller (uC) only provides 5v low current pulses. You need to build the hardware that uses the 5V pulses to provide 12V at the current levels required by the injectors. But you knew this.

The output voltage must be 12V and to effectively simulate use on a car or bike the frequency needs to be at least 96hz (6000rpm).

The uC will have no problem with frequency. Is the frequency fixed or do you want to ramp it up and down. If so we could use an LCD display to show current settings.

What about the injector pulse duration. Is it fixed or variable, do you want a mapping between freq and duration.

Obviously a fixed rpm/freq and duration would be the easiest.

 

[Brumby]

Hi Guy,
Im just wondering if this project ever got up and working. I am trying to do the same thing, Trying to pulse a 12v fuel injector at varying pulse widths basicly between 0-25 ms. Could anybody recommend something that be suitable

Thanks

 

[chris87654]

I'm adding to an old thread, but am planning on doing the same thing... Since I'm better at hardware, and it should be simple enough to make a square wave generator with variable pulse width and frequency (with protection for voltage spikes from coil shutoff), I figure I'd post this other link. I haven't watched the video yet but after reading comments I'm sure it's good.
https://hackaday.com/2011/01/16/20-fuel-injector-tester/

I already made an on/off jig to test fuel injectors before/after cleaning, but I think I've got one that sticks during operation (misfire in one cylinder). I would think a guy could hook up an o'scope to the drive voltage (from this generator) and see something if an injector is sticking - this after reading about using an oscope to look at ignition voltage on each plug/cylinder (is amazing how much you can see if you know what you're doing).

 

[alec_t]

Welcome to the forum. It is always best to start your own thread rather than dig up an old one which people may no longer follow. Your pulse gen seems to have nothing to do with USB, so the thread title will mislead viewers.

 

[chris87654]

Ah, I understand your point. I'd read through the thread and the last post struck me. It seemed like a dead thread - no one had an answer for the last guy. I'll be back after I get something working.... I'll include something like this
**broken link removed**
which shows an application for a USB oscope (this is how it should look). I've got a bad injector and don't want to pull the top of engine off again (after cleaning all injectors in a Chevy 2.8L), so want to diagnose it.

Picoscopes are expensive/$1500-2k (good software) but there are Chinese models (~$100) which work well but have low level software. Maybe the software guys could do something with it (I got a used 4-ch analog scope for about $300).

I didn't see anything about USB fuel injector tester with basic inet search. Would be nice if these guys could come up with something....

 

[alec_t]

So do you simply want "to make a square wave generator with variable pulse width and frequency (with protection for voltage spikes from coil shutoff)", or do you also need to know how to interface this to a PC via USB?
Have you considered using the PC sound card as a monitor for the injector current/voltage waveforms?

 

[chris87654]

DEFINITELY would like to do the I/O with a PC, but I don't know how to write PC software. I could do the output with a small 6802 computer I built in school (30 years ago - uses basic opcodes) that has a lot of parallel output lines , but using the sound card to read/record waveforms is very possible.... especially since the fuel injector pulses (likely) run between 1 to 10 ms (100 to 1K Hz) - there should be enough bandwidth to see the pulses and harmonics/anomalies.

I'll start with a simple pulse generator (hardware) and read result through the sound card.

I also saw this article that tells how to use a USB printer adaptor for "bit banging" (I assume means sending out parallel bytes).
https://hackaday.com/2013/02/21/bit-banging-through-a-usb-parallel-port-adapter/
Will have to read up on it, but it would only mean "printing" bit patterns with a time delay (printing I know how to do with a PC, but not how to make a time delay).

THANK YOU for the ideas!

 

[alec_t]

Using a simple pulse generator would provide the injector with a constant current for the duration of each pulse. However, I understand that injectors are normally driven such that there is an initial 'peak' current followed by a lower 'holding' current. The LM1949 IC can help with that. I suggest you check its datasheet.