Want opinions : Outdoors clock/temp_meter

[mabauti]

I'm planning to build a 4-digit clock & temperature meter for outdoors, but I can't decide among passive LCD, character LCD or 7segments leds.

Passive LCD
pros : low current consumption, big digits, kinda hard available
cons : hard to use/configure, fragile,

character LCD
pros : easy to use, text available, easily available
cons : small characters, fragile

7segment leds:
pros : big digits, easy to use, robust, easily available
cons : too much current consumption.

The main problem is :
both LCD : hard to see them at night (no sun light at all)
7segment leds : hard to see it at noon (lot of sun light)

Any comments?

 

[j.p.bill]

LCD displays are temperature sensitive. They have poor contrast or quit working when it gets too cold.

Make 7 segment characters out of individual LEDs. Use about 6 LEDs per segment. High-intensity blue LEDs against a black background will make you squint even in daylight.

 

[RODALCO]

You can buy excellent quality 5000 MCAD blue LED's on Ebay for around US$ 7.00 per 100.

 

[mabauti]

Hmm.. 6 leds per segment. Let's do the math :

6 x 7 x 4 + 2 = 170 leds total.

How much current will be required? I preferably want to use that clock/t-meter with batteries.

 

[on1aag]

Hi Mabauti,

I would personally go for a transflective LCD with a backlight.
The backlight would solve the problem of the visibility at night
and could also serve as a heater when the temperature drops
below freezing point.

on1aag.

 

[RODALCO]

If all 170 Led's are ON at 10 mA's makes 1.7 Amps.

But you have 6 LED's in series at 10 mA per LED, then 7x4x10mA= 280 mA's.

 

[RODALCO]

That is when all 4 digits show the figure 8.

In practical that won't happen. 20:58 hrs will be one of the highest type loads your supply will see if you use the 24 hour display option.

23 segments lit at 10 mA's makes 230 mA's at 18 to 20 Volts, take 3 volts drop per blue and 47 ohm series resistor per LED.

Most high efficiency LED's give off ample light at 10 mA's and don't require the usually 20 mA's designvalue.

 

[j.p.bill]

Of course there are other color LEDs that also come in high output forms. You can always get a couple of 100 LED grab bags and make the display segments arbitrarily large. That makes your investment in LEDs all of $4.00.

 

[mabauti]

The problem with leds is that they consume too much current and I'd like to power the circuit with a battery . My plan is to power the circuit with 3.3V @ 10A max ( just a first plan )

Will the bright (of the leds) be enough with 0.1mA?
________________
edited . 3.3V @ 10A max , must be : 3.3V @ 10mA max

 

[philba]

The problem with leds is that they consume too much current and I'd like to power the circuit with a battery . My plan is to power the circuit with 3.3V @ 10A max ( just a first plan )

Will the bright (of the leds) be enough with 0.1mA?

10A via battery? I'd buy stock in Energizer.

I bet you meant 10mA. No, the led will barely light up at 100 nA. You will have to use an LCD for that kind of current draw but then you will have the temperature issues previously mentioned.

 

[mabauti]

According with the local weather station records the lowest temperature has been 23°F and the highest 109°F.

I guess I have to follow what on1aag wrote