ecu voltage problem

S. Lastuka kicker at u.washington.edu
Thu May 1 03:13:26 GMT 1997


When we hook up the 6V radio shack supply we connect it directly to the
ground and power lines on the board, thereby bypassing the Voltage
regulator altogether. However the board has worked on an engine mounted on
the stand using the voltage regulator and the 12 volt batteries.  

I always thought 1 ms was awfully slow as well but the engine actually
idles with the 1ms event times at the injectors, very lean I suspect, but
running none the less.  The MCU is putting the 1 ms pulses on the pins of
the 1949's but the 1949's don't even get to hold state with that little
time.  

We are going to work all night on this as competition is nearing and
hopefully I can report back to you guys in the morning.  Also we don't
have it mounted in a box yet.  It was just a PCB sitting on the seat so a
metal box is being fabricated right now.  
Sean

 On Wed, 30 Apr 1997, Sandy wrote:

> At 03:28 PM 4/30/97 -0700, you wrote:
> >It is a truly bizarre glitch because the engine runs fine with our own 6V
> >AC/DC Radio Shack power supply and the same chip ran fine in the other
> >engine we have which is the same model but was mounted on a test stand.
> 
> Sounds bad, as 6VDC into a 7805 is not very good, Look at the LM2925, much
> better device. Is the battery 6VDC too? If the Power supply is not
> requlated, typically the output will be higher then 6VDC, enough for the
> 7805 to work properly where the battery at 6VDC is marginal. 
> 
> Watch out for rated voltage of CPU, as the Temp goes up the voltage
> required also goes up. Also the current drive from the LM1949's can be
> quite high also causing some odd glitches if the supply is already on the
> edge.
> 
> If you have a schematic that you could post that would help in finding the
> problem too.
> 
> The interesting thing, is that 1MS is pretty short to run injectors, I
> think the min time event for the faster injectors is closer to 1.5ms. 
> 
> A scope will be your best bet in finding the problem, check for clean power
> before and after the requlator. Check anything that you can stick a probe on 
> ;-).
> 
> It is not clear if the pulse from the CPU to the lm1949 is OK, Is that the
> source of the problem or is it the lm1949?
> 
> Sandy
> 
> >This indicates the code is capable of running the engine.  The motorola
> >chip actually generates the pulse and sends it to injector drivers
> >(National LM1949) which then open up the injectors.  The weird thing is
> >that the input pulse to the drivers (coming from the motorola MCU) is the
> >exact same length as the pulse from a crank sensor which happens to be 1
> >ms.  The pulse from the crank sensor feeds into the MCU for RPM
> >calculation and seems to work just fine regardless of power supply.  
> >Sean
> 
> 
> 




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