Jaycar 5300 LED display

[Peter Gargano]

I sent a reply direct to you on (your) Friday, but it bounced, so here's
some info. I've sent via the list.

> Crescent Kao wrote:
> 
>   After a few more days of tinkering with the display, I still couldn't get the
> calibration procedure to work properly... The dimmer definately works but adjusting VR2
> and VR3 with 1.4v and 3.0v doesn't change the display still.

If altering the "fake" sensor has no effect on the display, but the
procedure you outline below does, then it seems you don't have a good
fake sensor signal going to the modified FMD. You should measure the
fake sensor's voltage while you are varying VR2 and/or VR3 to ensure
the reading on the meter is what you're calibrating against (I have
DVM leads that I clip on to the display's input line and GND).

>   Anyways, I removed the R2 resistor from the board and decided to hook it up to the WB
> 02 in the vehicle, since that works just fine with a voltmeter. When I power up the WB02
> and the LED display (without starting the car - battery around 13.5v), the display
> prompty shows the "TEC" -> "11 c" and then will bounce between "10.4" and "10.5" and the
> bar graph will show nearly full rich (6 or 7th LED will be lit).

This shows the display is seeing something from the sensor input, and,
as noted above, indicates there may be a problem with the calibration voltage.
Remember, the calibration signal must be connected at the sensor input (1.4
to 3.1 volts), and the display's ground (GND).


> I then tried adjusting
> VR2 and VR3 at this point, and by doing so, it moves the display from around 10.2 to
> 11.2. The voltmeter on the WB02 at this time shows around 2.43v
>   If I start up the car (battery should be around 14v) the display will go through the
> "TEC" -> "11 c", 

The unit is indicating a reset sequence and this is quite normal.

> and then display "10 c" but the "c" will have a horizontal bar under
> it. Basically like the digit "5" but missing the lower vertial leg and the 8th led on
> the bar will be lit.

This display is documented and indicates the KC-5300 thinks the WB's output
voltage is less than 1.4 volts (but remember, you have not calibrated the display
so this is quite understandable).

>   Adjusting VR2 and VR3 at this point have no affect with the car started. The Voltmeter
> on the WB02 still displays around 2.43v at this time.

This indicates there is something fundamentally wrong (but probably quite
simple) with the way the display has been modified. OTOH, it's almost
impossible to get any meaningful kind of "calibration" settings with
the display connected to the DIY-WB *and* the motor on too!
 
> Can anyone shed some light on the situation? I have no idea how else to proceed in
> diagnosing the problem. Thanks again.

First you need to work out the problem with your calibration procedure and
make sure you can get the 14.0 and 30.0 calibration points set correctly.

Other than someone near you offering to check your work for obvious errors,
I can't think of any simple tests your could do.

Most problems people have with correctly constructed displays have to do with
the sometimes fiddly nature of the way the two PCBs are connected. 

Peter.

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