calculator LCD transmitter

[Hypnotize]

Hello
I have an 8 digit display calculator (the standard ones you buy cheap). I want to send the LCD data to a remote LCD using RF transmitter. I tried to get the datasheet for the LCD display so I would know how many bits I should send and what is the pinout but couldn't find any. Can someone help me with this?
I am also looking for a nice RF module transmitter\receiver type.

thanks,
hypno

 

[Nigel Goodwin]

The LCD display will be multiplexed (and probably triplexed), it's also fed with AC rather than simple switched DC - so it's not at all trivial to read the data from it.

 

[penoy_balut]

you need a microcontroller to read and transmit data thru RF while on the other end decoding and displaying the data.

 

[Hypnotize]

I know how to do that, I just need the datasheet of the LCD. If someone could link me to a standard LCD 8 digit display dataheet I should be able to do it. the LCD is not fed with an AC, the battery in the calculator is DC. Maybe the calculator chip inside sends square waves to the LCD but I don't think so.

 

[penoy_balut]

calculator LCDs are not standard design, you'll be having difficulty finding datasheet, use standard LCD module based on HD44780 instead, datasheet is available on the net

 

[evandude]

I know how to do that, I just need the datasheet of the LCD. If someone could link me to a standard LCD 8 digit display dataheet I should be able to do it. the LCD is not fed with an AC, the battery in the calculator is DC. Maybe the calculator chip inside sends square waves to the LCD but I don't think so.

LCD's like used in calculators are usually custom-made for that particular device, which is why you can get calculators and electronic toys and things like that with custom symbols and things on their displays. Thus searching for a datasheet for a device that is proprietary and not separately commercially available is an exercise in futility.

Not to mention, usually in calculators and similar devices, the connection between the board and LCD is made via a weird stacked conductive rubber strip that is sandwiched between the LCD and conductive pads on the controlling PCB. To make connection to all of those pins, you'll have to either scrape off a lot of solder mask and end up with a heap of very small solder joints just waiting to be ripped off, or go around and solder wires to all the destination pins. Either way it's going to be a big ratsnest of wiring, and probably not work at all if you're not very good at soldering.

And yes, I think we all realize that a battery provides DC voltage and not AC. But LCD's that are directly driven like that ARE driven with AC. Your unfounded belief that that is not the case leads me to believe that you probably aren't aware of how much of a headache this project idea of yours would turn out to be, and it sounds like you really ought to reconsider what you're doing.
Let me put it this way, it would be easier for you to make a calculator from scratch with a microcontroller, using a standard easy-to-use character LCD with an on-board controller, and add this RF thing you want to it, than it would be to do what you're trying to do.

 

[bananasiong]

For displaying numbers from microcontroller to a few 7-segment display, many output pins are needed. Is there any device which can converts serial to parallel in 8 bits? So that one output pin control one display.

Thanks

 

[Nigel Goodwin]

For displaying numbers from microcontroller to a few 7-segment display, many output pins are needed. Is there any device which can converts serial to parallel in 8 bits? So that one output pin control one display.

Yes, a standalone UART (if you can still get them?), but a simpler (and cheaper) solution is to use a microcontroller to do it. But in any case, you generally multiplex such displays, so they use less than you might think (4 seven segment displays only require 11 pins).

 

[Ayne]

It is my idea for reducing the pin count and increasing the 7Segment Display.
If i am wrong then guide me....experts

 

[Nigel Goodwin]

Well I'm not commenting on the exact wiring, and if it would work as shown, but that's a standard method of multiplexing - it has the obvious disadvantage of requiring an extra IC though. You can also use a 4511 LED driver to reduce the pin count to the segments.

 

[jbeng]

... a weird stacked conductive rubber strip ...

A device known as a "zebra strip" or "elastomeric connector".
JB

 

[kchriste]

It is my idea for reducing the pin count and increasing the 7Segment Display.

Look at using "CharliePlexing". The link below shows how to control 8 digits with 9 pins:
**broken link removed**

 

[mindctrl]

Maybe everybody is making this more complicated then it needs to be.... Have you looked at using one of these?

https://www.sparkfun.com/commerce/categories.php?cPath=16_79

Hope that helps a bit.

 

[evandude]

Maybe everybody is making this more complicated then it needs to be...

I don't think so, because everyone's been talking about the difficulties in actually reading the state of all the display segments, let alone transmitting that information.

 

[geckohml]

jeje, looks like you want to cheat in a test, that´s a good idea