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Question about LCD's

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Space Varmint

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Hi, I wish to use a serial interface to an 5 digit position, 7 segment LCD. I am planning to use a 74HC595 serial-to-parallel shift registers. I am choosing these because the outputs can be latched. The outputs are also tri-state so my question is:

Do you think it is possible to alternate from high Z output back to latched data in unison with the back plane signal to get the LCD segments to display the correct data?
 

kchriste

New Member
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No need to tristate the latches. Just drive the segments 180deg from the backplane when you want them on and 0deg when you want them off. A 30-60Hz backplane squarewave should work OK. So as long as your processor and serial interface can toggle the latches at that rate, you should be fine. As mentioned by BlueRoom, DC is a no-no for LCD direct drive.
 

Space Varmint

New Member
No need to tristate the latches. Just drive the segments 180deg from the backplane when you want them on and 0deg when you want them off. A 30-60Hz backplane squarewave should work OK. So as long as your processor and serial interface can toggle the latches at that rate, you should be fine. As mentioned by BlueRoom, DC is a no-no for LCD direct drive.
That's my point. I want to leave the data in the latches alone and toggle the tri-state and back plane. You know from high Z to driving.
 

blueroomelectronics

Well-Known Member
Yea build in LCD controllers, set & forget. What were you planning to connect it to?

The 16F917 is a typical LCD PIC. It can control LCDs with up to 4 commons.
 

Space Varmint

New Member

blueroomelectronics

Well-Known Member
Yes the 917 is a big chip, depending on your LCD you might be able to use a smaller PIC. Your PK2 simply connects to VPP,VDD,GND,PGD & PGC (all clearly labeled on the pinout for the 16F917) Just hook em up and you're good to program.
 

Space Varmint

New Member
Yes the 917 is a big chip, depending on your LCD you might be able to use a smaller PIC. Your PK2 simply connects to VPP,VDD,GND,PGD & PGC (all clearly labeled on the pinout for the 16F917) Just hook em up and you're good to program.
Roger, got ya. So just make my own board from the 5 pins of the PicKit2 over to the chip? Because I didn't even see an adapter board for the 40 pin your using.

About your code. Is your handle "cricket" in the forums? Is that where I look? I'm definitely interested in your code.
 

blueroomelectronics

Well-Known Member
I use a 5x2 connector for my ICD connector. The 16F877A uses the same programming pins as the 16F917
They are the same order as the PK2s first 5 pins. Just make sure you have a 22k resistor from VPP (pin1) to VDD
 

Space Varmint

New Member
I use a 5x2 connector for my ICD connector. The 16F877A uses the same programming pins as the 16F917
They are the same order as the PK2s first 5 pins. Just make sure you have a 22k resistor from VPP (pin1) to VDD
Yeah I see them here:

• ICSPCLK
• ICSPDAT
• MCLR/VPP
• VDD
• VSS

I think I want to use this PICLF1936. It's only 28 pins and comes in the slim DIP package. It has 60 segment controls where the PICF917 has 96. Your code is probably the same for both. You know how PICs are. Let me check your web page. Do you have a link to your code?
 

blueroomelectronics

Well-Known Member
It was only partial code showing how to setup the LCD registers and it's in the thread here. The beauty is once setup it runs all by itself. You just set the bits and it displays them.
 

Space Varmint

New Member
Nice work! Killer Diller!

Got a question for you. Is your code for that dot matrix LCD? I hope not because I just want to use a seven segment right now. Hey, how did you do those PCB illustrations? That's really neat! :D
 
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