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?

 

LCDs need an AC style signal, DC latches are not good for them.

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Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

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.

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Inside every little problem, is a big problem trying to get out.

 

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.

 

There are PIC microcontrollers with LCD drivers in them, easy to use too.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

IN THEM? I didn't know that. I have used their AY0438 but it's only 4 & 1/2 digits. I need 5. Well, thanks I will loo into that. Sounds better!

 

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.

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Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

Cool Blue! I'm looking at this one here:

http://ww1.microchip.com/downloads/e...Doc/41364B.pdf

I'm on page 393. I guess the SPDIP could be programmed on the PicKit 2? I would just need to make an adapter cable.

Yeah, I want to use the LCD section for a freq counter.

 

Oh man, I am playing hell installing MPLAB v8.36

 

The PK2 programs pretty much the entire line. If you search for my old cricket threads you'll find a schematic and code snip.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

Did you get a new adapter board like this 28 pin?

Product Search - microchipDIRECT

I guess I need new PicKit 2 software too. The '917 you used is 40 pins isn't it?

 

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.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

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.

 

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

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

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?