alphanumeric lcd display powering

jmurba

juste some more thoughts pete if you permit me,
In fact designed the gauge under the supervision of a sattelite ingineer (that also dives the gauge !!!!), he ended thinking exaclty like you except that he thinks that the zener regulation should be only implemented to the display and the microcontroller supply (the microcontroller/display logic links also must not exceed 5.5 volts) .
that way the rest of the circuit would continue to be supplied with the baterry tension (op amps, buzzer , leds etc etc).
it would limit the extra consumption to the stric minimum as the pic and the display don't consume a lot unlike the buzzer and the hud led<;
in addition using a 5,4v zener tension would be great cause the zener would work only while the battery tension (minus the diode drop 0.6v) is above 6 volts, afterward from 6v to 5.1volts (the low limit of the display ) the zener would stop dissipating power to the ground and lets thing go normally till the end of the batterry life.
just great
thanks a lot
regards
jean mi

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Genesis

I would be careful with the zener if you intend to drive any sort of load.

On the K1 I have a split-supply system.

V+ rail voltage drives the buzzer and solenoid coil.

V+ is applied to a LDO/LDV regulator - with care you can get good efficiency and very low quiescent current, plus low drop-out voltage (little overhead required over the desired rail.) The output of that feeds the LCD and CPU, plus the logic supply for the potted in-head components (which contains the A/Ds, op-amps and instrument amps plus protective circuitry and such for the inputs)

The logic board in the display case has a jumper to allow the use of either 6V or 12V buzzers, and this allows the use of either 6V or 12V solenoid coils as well; the system works equally well with either. I am using a light can battery right now, so I am set up for 12V, but it will run fine on a +6V supply - you do have to make a change in the config tho so the system knows where the low voltage warning point is (it tracks it via one of the ADC channels)

The CPU will run down to +3.4V, long after primary regulation is lost.

If you actually manage to reset the CPU due to low power, you REALLY ran it flat and nothing other than the display and CPU have been working for quite a while (HOURS)

Beware that backlights draw quite a bit of current - I have a PWM controller built into my display driver, so my average current draw with the backlight on at 2% is minimal - but with it "on" current consumption for the backlight ALONE is about 70ma! That's is BY FAR the largest consumer of power (other than the solenoid) in the system.

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PeteS

The simple resistor / zener combination is only good for steady loads. Losses go through the roof if you start having to supply variable loads.

Agreed. Only put on the backlight if you really need it.

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Pete S.

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jmurba

++++ I have no back ligth, I don't want any

regards

jean mi

__________________
when will I be able to think about something else then spending hours underwater, when will I be normal ?

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