3 volts lcd displays

jmurba

Hi all,

I built a pic jauge.....i run 3 sensors alarms, time etc....
The thing is that I use a 5 V power supply.....
I Recently decided to implement an intersema depth sensor to get a deco algo in the tube but of course when the samples arrived at home a realized that it was a 3 volts sensor.....
Well I have to switch al the circuit to a 3 volts supply, it is not a problem for the pic, not a problem for the op amp... but I did not find any display running in 3 volts.....
I've lingered on the web but in vain.....
Some may have the same problem to find a display working with a 3,6 lihium bat.... all computers does work on this tension ... why the hell can can't i find one !!! (-:
ps i would not like to use a dc/dc

regards

jean mi

paulraymaekers

salut jean-mi, hello

if it is such a problem, look what component takes most of the current, and eventually you take a big 3.6 for all the rest, and a dual coin cell (6V) for the display
regards
paul

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Stephane

Hello Jean-Mi,

You can use a low power, low drop-out voltage regulator to make the 3V.
Go and have a look on Farnell's website to get some part numbers.

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jradomski

no big deal use a charge pump.. 1 ic and 3 capacitors...

I usually use the ltc1517-5, the maximum current it can deliever depends on the input voltage and how much droop you are willing to accept..

with an input >=3v you can expect 20ma at 5v, 40ma at 4.9v (3v input) or 60ma @4.9v (3.3v input) (most displays work reliably down to 4.5v)

Conversion efficiency is over 80% for any load greater than .1ma

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steevke

JM,

you can also use an ultra low drop-out regulator (like the TPS79733) on a small dedicated PCB on which you also mount the intersema sensor. You then use flatcable from main PCB to small intersema PCB.

HTH

steven

jradomski

This COULD be a problem.. You need to look at the maximum voltages allowe for each device IO and what the threshold voltages are.. the normal High threshold is .8 X VDD so if vdd is 5v the device thats powered by 3 to 3.6v) needs to be able to bring the output to 4v which is beyond the rail (and besides intersema only guarantees that the high output is 75% of ITS VDD), so now you need a level translator..

Also you MUST look at what the max voltage in on the IO lines for the pressure transducer is (this is not specified by the manufacturer)

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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

steevke

I don't see why - he runs his LCD and PIC at 5V. He uses this 5V to feed a small PCB onto which he mounts his LDR + Intersema sensor, caps and connector. Main PCB including display runs at 5V, Intersema PCB runs at 3.3V.

The intersema needs a 32k clock, SDI, SDO, SCLK. Add +5V and GND (to feed the LDR on the small PCB) and this is perfect for a 6pin wide flatcable.

steven

jradomski

except the logic levels need to be correct, Intersema doesnt say what voltage it can take on an input, the protection diodes could be damaged if the voltage is above the design threshold, but since they dont specify, the imput MAY BE 5v tolerant, howveer the output from the sensor will not meet the required voltage levels for the PIC since it is operating at 5v.. The high threshold is determined by the supply voltage, the higher the supply voltage the higher the high threshold is.. When you dont meet these levels the input is indeterminate, sometimes it may work as you want othertimes it wount, and without knowing the output stage on the device using a pull up resistor may not be safe either (typical problems could be damaging the device, or excessive power consumption)

The intersema data sheets don't list an absolute rating for its inputs but its specified 2.2 to 3.6v depending on VDD

NOT using level translators to the LCD is normally OK as long as you are only writing to the display and not looking for any output from it.. The thresholds for the most LCD are withing the output range of a typical microcontroller operating at 3v. If you want to get info from the LCD you would need level translators as well..
The input characteristics for PIC devices (since you said you were using a pic but didn;t state the family) vary greatly even within the same chip..

for ports with TTL inputs for 5v the threshold is 2v, but for ports with Schmitt trigger its typically 80% of VDD, so you need to look at your port requirements closely..

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Joe Radomski
CCR Trimix Instructor Trainer
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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

Stephane

Joe, Intersema on its website gives an application note (AN505) that show how to interface the pressure transducer to a printer port of a PC. They use 74LCX04 inverters (under a 3V supply).
Pretty simple no?

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Tom Rose

Until recently most sensors utilized 5 volts and all was right with the world....Now requirements are dropping...and low dropout voltage regulators are necessary.....

I've attached a simplistic diagram

Tom

Attached Images

circiut for 3 volt sensor.jpg (16.9 KB, 268 views)

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