3 volts lcd displays

jradomski

The part you state IS a type of level translator.. its used to interface high voltage systems with low voltage ones..

I'm not trying to be a know it all just pointing out that each interface requirement has to be considered besides the voltage requirements of the supply.. There are so many logic family's today that multiple things have to be considered, its alot worse than the days of just cmos-ttl interconnect problems.. Where even the same voltage supply didn't necessarily mean the 2 could be connected directly..

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

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

steevke

You're right Joe - I didn't consider the logic levels. Nevertheless he can still use the principle of using a seperate PCB running at 3.3V - he just needs to add the level converter to be safe.

steven

jmurba

Hi paul,

thanks for help, but in fact it is not only a sypply probleme but also a communication problem, the microcontroler and the other component are are communicating all the time via parallèle or series busses , so they need to have have the same supply voltage and commond ground.
I think that sending parralele bytes and serial spi bytes from a 3 volt pic to a 5 volt display or from a 5 volt pic to a 3 volt sensor will not give us good results.

well not easy.... I though i was ok with my bluddy gauje that works when i suddently decided to implement deco cause one my computers drown....

so i must re make all the studdy......

that's life....of the home builder ((((-:

regards

jean mi

jmurba

salut

yes there are many solutions like that but it is not natural to make 5 volts and 3 volts component speak to each other....I am gonna give it a try but i am quite sure it is not a good solution.

regasd and thanks

jradomski

Jean mi,
I have used 5v displays with 3v cpus and logic many times.. If you are not trying to get data FROM the lcd only TO, then the interconnect is simple on most MCUs.. You need a common ground and the 5v to the displays which is easily done with a charge pump.. Once you need 2 way communication you need level translators between the devices at different supply levels, the it doesnt matter if you use charge pumps or LDO..

If you are using graphic displays over SPI, then you have 2 choices, use the ram in the lcd to save transfer time but now you need to translate voltage levels, if you buffer the screen in the microcontroller, it again becomes an aoutput only and you dont need level translators just more internal ram.

BTW the Intersema sensor is not SPI, but be used over an SPI bus if done correctly..


I prefer to run everything at as low a voltage as necessary so the device uses as little power as possible.. in this way charge pumps are very efficient.. LDOs are good when the supply of the power source is near the required output, otherwise you waste power by generating heat..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

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

jmurba

Dear Joe ,

thanks a lot for advice, I am gonna take my test board out of it's case an start testing that.

so let's go for a charge pumps and a common ground

As for the intersema communication protocol, the application notes states that spi master slave is well the bus.

see there http://www.intersema.ch/site/technical/files/an510.pdf

regards

jean mi

jradomski

The an tell you how to use a common SPI bus to do the communications, but by the book it is not a true SPI slave..

On a true SPI bus there can be multiple slaves, where the selected one is chosen by the assertion of a chip select signal. This is not the case for the intersema pressure sensor.. the communication to/from this sensor is dependent on specific data sequences to start and stop transmission.

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

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

jmurba

Hi Joe,

ok anyway I am gonna test the transmissions soon, an will all know if a managed to do it properly or not.
I hope it will work.
did you use it ?
don't know what sensor to use otherwise,

thanks again for your advice it great to be able to get info in the community that way.

regards

jean mi

stephengrenfell

Jean-Mi,

There are plenty of Graphic LCD modules that work at 3v (like the one I showed you). But you are right there does not seem to be any character LCD display modules that work at 3v. This might be becuase the driver IC (built into the module) only exists for 5v. You could use a graphic LCD module - but you will need the SW to create the characters. Otherwise you could use a DC-DC charge pump (small IC) to double your 3v and use this to drive your LCD (they will operate at up to 7V (normally).

Stephen

stephengrenfell

Jarod is right the Intersema device is not true SPI - the main differences are that there is no CS instead you need to turn the SPI clock off (the Intersema spec suggest using a tri-state buffer for this), and when the module is ready to send data (i.e. after a measurement sample cycle) it changes logic level on tx data pin - so you need to detect this with an interrupt. You can still use it with other devices on the SPI bus provided you deal with these two issues. This is not insurmountable - it just needs soem careful thought.

Stephen