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Topic: LCD shield and/or LCD serial backpack (Read 35552 times) previous topic - next topic

mem

#30
Feb 07, 2008, 11:24 am Last Edit: Feb 07, 2008, 11:25 am by mem Reason: 1
Cheater, sounds good, looking forward to hearing when you are ready to ship.

According to the oz post web site, items smaller than 260mm x 360mm and under 20mm in thickness count as a letter.

Cheater

http://www.megaupload.com/?d=AXTX2AHO
There is the brd and sch files for it. Can someone double check it? ;)

It features a ATmega8 core with Power, SPI, I2C, Serial, Reset and Wait pins on one side.
The other side matches a LCD's pinout including backlight pins.

Two transistors power the contrast and the backlight.
The contrast one has a capacitor to try and smooth out the voltage. I'm thinking 0.1uf but I'm not sure.
I'm also not sure if the resistor on the contrast transistor is required. If it isnt then it means less parts to worry about.

The pull up resistor for the reset pad will be 10k.
I'm not sure about the lcd backlight one. I use 100ohms on my lcds and it works fine but I'll be reading the datasheets to be sure.

Any suggestions for part values would be greatly appreciated.
I'm going for low part count because Futurlec only sells in batches of 5,000 and I dont want too many different values.
My main concern is the contrast capacitor.

kuuk

looks like you have to be registered to get the file from megaupload!? maybe rather post an image file, so we can see it here?


mem

Quote
looks like you have to be registered to get the file from megaupload!? maybe rather post an image file, so we can see it here?

kuk, you just have to wait a minute before it does the download. The invitation to register is for instant downloads.

I got the file and a quick glance on eagle looks good. But I don't have enough PCB design experience to review the design.

kuuk

ah, thanks. i think i got distracted by the german translation of the page :-) looked like a redirect.

mem

kuk, es gibt kein problem  :)


cheater, I have 3 or 4 LCDs in my parts box and wonder if its worth testing the contrast and backlight circuits on them using my arduino. If you want to modify the transistor driver code so it works with the arduino's  timers running on a 16mhz clock then I would be happy to test this on my breadboard.

I don't need the code for the LCD data for this test but would be happy to look at that if it would help you.

Cheater

Thanks mem. I'd love it if you could test PWM with a 0.1uf capacitor on the contrast.
I'd do it but I dont seem to have any transistors around. I could scrounge one....

No code yet. I'll whip it up once I get the PCBs. :)
Just test with AnalogWrite for now.

I've created a Sourceforge project for this to keep everything nice and tidy.
I'll be setting it up today.

Cheater

Just tested (very roughly) without a transistor and it seems that the contrast acts just like a normal LED.
Ripple isnt a problem. A 0.1uf capacitor should just smooth things out a bit though.

Ok last questions:
Is a resistor required on the LCD's backlight? Sparkfun doesnt use one. I'd imagine it would be fine.
And is a resistor required on the transistor's base? I wouldnt think so.

I will be rather happy if I can ditch two resistors. :)
I'll then be able to order.

Current parts list (assuming I can ditch two resistors):
2x 0.1uf 0805 capacitor
2x BC817 SMD NPN transistor (0.8A max)
1x 10k 0805 resistor
1x ATmega8 QTFP

Cheater

My bad. The ATmega8 doesnt have enough PWM and I forgot about slave select. :)
I've now got it with a ATmega168 which has more PWM and more space which should be good.

Cheater

Just a update: I have the OpenLCD website up.
http://openlcd.sourceforge.net/

Eagle files (completely different to whats posted above) are in SF's release system.
http://sourceforge.net/project/showfiles.php?group_id=217002

Can someone do a quick check on the circuit to make sure it will work before I order a large stack of them?
I figured that its only slightly more to get ~138 of them as it is to get 25 of them so why not.
I dont want that many coasters though. ;)

chrisco

Just a question: You do not provide a ground signal to your SPI, SER and I2C connectors. I would have expected these to have a ground since they are not differential. Am I missing something?

mem

Cheater, The 3d view shows the header pins for the LCD and arduino interface on the same side of the board.  If I am visualising this correctly, I presume the arduino interface header will be mounted on the opposite side of the board to the LCD header.

Cheater

Quote
Just a question: You do not provide a ground signal to your SPI, SER and I2C connectors. I would have expected these to have a ground since they are not differential. Am I missing something?

Yes your missing the 5V and the GND connector on it. ;)
The user will have to connect all the grounds together themselves if power and signal are coming from two different sources.
Quote
Cheater, The 3d view shows the header pins for the LCD and arduino interface on the same side of the board.  If I am visualising this correctly, I presume the arduino interface header will be mounted on the opposite side of the board to the LCD header.

Yep. The 3d view looks pretty but its not perfect.

Btw xSmurf made me add RS232 to the list of interfaces it supports. :)
Going to see if I can fit a crystal on it, if not then I'll order.

Severino

There was a demo of a LCD shield at the last NYC hack lab.
Mike
www.liquidware.com

Cheater

Well 100 PCBs are now coming to me along with 4,000 capacitors and 5,000 resistors. :)
I'll have enough to populate 30 PCBs. The Atmel chips get expensive quicky ($100 for 30).

Around half are earmarked for this first run so about 10 will be for sale. :)
If they are popular then I can have another batch ready within about 5 days after that.

Quote
There was a demo of a LCD shield at the last NYC hack lab.

Interesting. Got a url?

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