Driving 3 1/2 segment LCD

[edeca]

I've had a quick look but I can't seem to find any generic driver ICs. Is there anything that can easily drive a 3.5 segment LCD? They require a lot of I/O lines and I don't really fancy using a huge PIC to do it.

It seems that driving a small 8x1 LCD would possibly be easier.. all I want to display is a temperature.

 

[BeeBop]

I've had a quick look but I can't seem to find any generic driver ICs. Is there anything that can easily drive a 3.5 segment LCD? They require a lot of I/O lines and I don't really fancy using a huge PIC to do it.

It seems that driving a small 8x1 LCD would possibly be easier.. all I want to display is a temperature.

Yes, driving a small LCD with an on board controller will be so much easier... so much quicker to implement.
Microchip, Atmel et al make micros for this, but an 8 x 1 or 8 x 2 display with the built in controller is very common, so there are lots of examples to look at.

 

[ericgibbs]

I've had a quick look but I can't seem to find any generic driver ICs. Is there anything that can easily drive a 3.5 segment LCD? They require a lot of I/O lines and I don't really fancy using a huge PIC to do it.

It seems that driving a small 8x1 LCD would possibly be easier.. all I want to display is a temperature.

hi,
This is one way, using just 4 wires.

If you dont want to use the large ic, use a HEF4035 S/R with T/C outputs, one for each digit.

 

[Mike - K8LH]

Bill (Blueroom) posted an example LCD driver awhile back using one of the special purpose PIC devices with low level LCD support built-in...

Mike

 

[edeca]

Bill (Blueroom) posted an example LCD driver awhile back using one of the special purpose PIC devices with low level LCD support built-in...

Ah yes, I had forgotten all about those. I don't think I have one here, perhaps that will have to be my next sample

All I need is A/D, a few inputs and a few outputs so pretty much any PIC should do. Annoyingly is seems that the smaller devices share their analogue ports with the LCD segments.. it might be possible to work around that.

I'll search for Bill's code.

Thanks for the tip!

 

[blueroomelectronics]

I've used the 16F917 to drive the seven segment LCD glass on this thermostat prototype.
It's really easy to use those displays once you wire em up. And it does support 3V thru 5V displays (you use voltage divider resistors)
**broken link removed**

 

[edeca]

That's pretty much what I'm building, only with a relay output to control a very small heater. I've got some Microchip linear output thermometers which work really nicely when coupled with a voltage reference.

Where did you get the LCD, does it have dots between the numerals? It seems to have far fewer pins than others I have looked at.

Just have to hope that the required pins for VREF and ANx aren't shared by the LCD circuitry, I'll check the datasheet.

 

[BeeBop]

I've used the 16F917 to drive the seven segment LCD glass on this thermostat prototype.
It's really easy to use those displays once you wire em up. And it does support 3V thru 5V displays (you use voltage divider resistors)

Wow, thanks! Got to take a closer look at that one.

 

[arhi]

I've used the 16F917 to drive the seven segment LCD glass

Hi blue, I have skimmed the datasheet and was unable to find the answer to the following question ...
- does the "segment driver" mean that I do not have to add the resistors to limit the current but just to attach the output of the pic directly to lcd?
- is there a difference (in setting pic, adding current limiting resistors, adding driving transistors ... anything) when driving glass lcd or standard 7seg led driven display (I have actually never used the glass ones)

thanks

 

[blueroomelectronics]

LCD and LED displays are very different beasts, LCD displays are AC driven (DC can damage them) No current limiting resistors are needed but if you drive an LCD in a mux you need to setup the voltage divider as in the datasheet. Don't use the 917 for LED displays.
And yes the LCD segments attach directly to the 917

 

[arhi]

LCD and LED displays are very different beasts, LCD displays are AC driven

wow.. interesting .. not to go off topic any more, I will go first trough the LCD display data sheet ... (I never used them before and I assumed they use DC just like normal LED display, only that they use less power)

Thanks for the answer

 

[blueroomelectronics]

They use very very little power, I've been running the prototype off batteries for months. You don't want LED 7 segment displays on a thermostat if the sensor is too close (they will heat up the sensor a couple of degrees).

 

[ericgibbs]

wow.. interesting .. not to go off topic any more, I will go first trough the LCD display data sheet ... (I never used them before and I assumed they use DC just like normal LED display, only that they use less power)

Thanks for the answer

hi arhi,
LCD's are driven by a back plane [BP] square wave, osc freq range about 100Hz.
If you look at a LCD pinout you will see the BP pins, sometimes more than one, all must be connected to the osc.

LCD's will run from dc signals, but very quickly the segments will start turning black.

 

[arhi]

thx eric ... did some reading so I get the picture now .. I thought that they are the same, but after bill told me they are not, I did the necessary reading .... anyhow, it was not my intention to steal the thread ... thanks for the explanation .. I ordered few different glass lcd's and few 16f917 so I'll play with those (in 3 weeks when they arrive) might be interesting as I mention already - I have never used them before (mostly because I was unable to find ones with "pins" but only ones that you need to connect to pcv using some rubber "thingy" - now I found a local supplier that is reseller for microchip, dallas, ampire, ftdi, maxim, rabbit... and many more - so finally I can order "anything" and get it in worst case scenarion - in 3 weeks - I already stockpiled a bunch of MC opamps and comparators )