13 replies to this topic

[jimox]

I want to control a HD44780 LCD with a 74HC595 shift register like Szymon has done in http://geekswithblog...id_crystal.aspx . He has a wiring diagram in the post but his picture of the backpack that he made has a resistor in it yet his diagram does not so I am not sure the diagram is complete. Before I go and attempt this (I am a complete newbie and a bit hesitant) I wanted to see if anyone had a complete wiring diagram so I feel a little more comfortable that I am not going to kill any components. Thanks.

[Stefan]

I got that think working, with resistor for the backlight, but that's an adjustable resistor (Potentiometer). Here's a picture of my board: http://nederland.lig...05_IMAG0458.jpg It's always good to set it up on a breadboard before soldering though, just to make sure everything is in the right spot.

[jimox]

Stefan, Thanks that is exactly what I needed. Last night I wrote my first program for my netduino and today I am already planning on LCD displays. I can see where this could become a dangerous addiction!

[Dan Morphis]

Stefan, Thanks that is exactly what I needed. Last night I wrote my first program for my netduino and today I am already planning on LCD displays. I can see where this could become a dangerous addiction!

Welcome to the community! I remember how exciting it was for me just a few short months ago when I got my Netduino and had code working in under a few minutes. It was a very different from the experience I had with other embedded platforms I've tried over the years. I could instantly be productive!

If you haven't already, you may want to checkout the hardware getting started buying guide I've started on in the wiki. It covers breadboards to oscilloscopes, and all the main passive components in between and where to buy them.


-dan

[jimox]

Dan, Thanks that info is great. I am a .NET developer and as such the software side comes easily but the hardware has always been a bit of a mystery. The info on the wiki is great and the starter list has been very helpful (I just bought Getting Started in Electronics today). Thank you guys for putting that together it really has been helpful. --Jim

[jimox]

So I was able to wire this up exactly like http://geekswithblog...id_crystal.aspx and it worked great. Now I am trying to create a backpack which will require the wiring from the shift register to the lcd to be "backwards". So I tried just like the attached wiring diagram however it doesn't seem to work. Two issues (which I think are separate) The backlight flickers and the readout just shows up as one row of boxes. I did use the Shifter74Hc595LiquidCrystalTransferProvider from the blog post and set the bitorder to LSBFirst. Anyone see any problems with my wiring? Thanks.

*5/25/11 - Edit: I removed the bad wiring diagram to keep anyone from mistaking it as working.

[Mario Vernari]

Hello.
A fully working example is here. I built in the same way and it worked as soon.

It seems that your wiring does not match the expected driving assignment. Compare the HC595 to LCD wiring of your and Szymon's pictures.

The black blocks show because you must adjust the contrast of the LCD.

I would not use a trimmer (potentiometer) for the backlight: it is useless and there are different and better ways to adjust the brightness. However, a step by step first.

Hope it helps.
Cheers

[jimox]

Hello.
A fully working example is here. I built in the same way and it worked as soon.

It seems that your wiring does not match the expected driving assignment. Compare the HC595 to LCD wiring of your and Szymon's pictures.

The black blocks show because you must adjust the contrast of the LCD.

I would not use a trimmer (potentiometer) for the backlight: it is useless and there are different and better ways to adjust the brightness. However, a step by step first.

Hope it helps.
Cheers

Mario,

Thanks for the reply. I have been able to get it to work when wired exactly like Szymon's example. What I am struggling with is the "upside down" wiring from the shift register to the lcd that Szymon's backpack picture uses but he doesn't have a wiring diagram for. This is necessary to keep the backpack compact since the lcd pin's will be reversed from his original wiring.

As for the contrast I have checked with the trimmer at 0% & 100% and I still get the black blocks but just dimmer. I am sure that it has something to do with my attempt at the "upside down" wiring I just am not sure what. I think tonight I will rewire it back up to the original wiring scheme then take another shot at reversing the data out with everything else exactly as it was when it worked.

As for pulling the trimmer out on the backlight, I will do that thanks for the advise.

Thanks again,
--Jim

[jimox]

OK, I finally got this working. As usual it was stupidity on my part. When I reversed the wiring between the shift register & the lcd I missed Qa (pin 15 on the 74HC595). If anyone is interested I have attached an updated wiring diagram (I am new to fritzing so please forgive the quality). Thanks everyone for your help. --Jim

Attached Files

•  LCD.png   96.03KB   222 downloads

[Szymon]

OK, I finally got this working. As usual it was stupidity on my part. When I reversed the wiring between the shift register & the lcd I missed Qa (pin 15 on the 74HC595). If anyone is interested I have attached an updated wiring diagram (I am new to fritzing so please forgive the quality). Thanks everyone for your help. --Jim

Great news that it works for you and nice work on documenting the diagram!

Thanks,
-Szymon

[jimox]

Great news that it works for you and nice work on documenting the diagram!

Thanks,
-Szymon

And a special thanks to you Szymon. It was staring at the highres photo of yours that you sent me that made me finally see the wire crossing over from pin 7. That was all it took to have the aha moment.

[Mark S]

Jimox, I have searched high and low for an actual parts list for Szymon's LCD example discussed above from the geekswithblogs photo, but have not found it. Now that you have it working correctly, does this list look correct? 16x2 LCD (HD44780 chipset) 16 pin connector 16 pin socket (2x8) 74HC595 10k pot 2n2222A transister Mystery resister (320 ohms?) And back to your original thread question, is the mystery resister required? And if so, from where, to where? Is my guess correct at 320 ohms? Also: Is the backback in Szymon's original picture backwards? I'm confused which picture and Fritz to use. Assuming I set mine up visually the same as his, I should stay with his Fritz right? Then the only question is the mystery resister. Where did you end up getting the Liquid Crystal library? Thanks to both you and Szymon for your efforts! =) ~Mark

[jimox]

Mark, Here is what I used: HD44780 http://www.adafruit.com/products/181 16 pin header (mine came with the lcd) http://www.sparkfun.com/products/116 10k pot (mine came with the lcd) http://search.digike...3386F-103TLF-ND 16 Female headers http://www.sparkfun.com/products/115 16 pin dip socket http://www.sparkfun.com/products/7938 74HC595 http://www.sparkfun.com/products/733 2n2222A I had mine but I think http://search.digike...e=P2N2222AOS-ND should work. Then comes the mystery resistor. I did not use one. But if you look at http://forums.netdui...ot-wall-adapter I have recently found a problem when the netduino is plugged into the wall. I am starting to suspect that the mystery resistor might be the fix. I am going to send Szymon an email and ask what he used the resistor for (I will also ask what size) I'll let you know what he says. As for the library you can get it at http://microliquidcr....codeplex.com/. Finally which wiring to use can be a little confusing at first but the diagram that is on his blog is if your lcd's pin 1 will be on the far right mine is if pin 1 will be on the far left. I promised Szymon that I would write all of this up and put it on the codeplex wiki. I hope to be able to find time to do that this weekend. Hope this gets you started, if you have any other questions let me know. --Jim

[Szymon]

I am starting to suspect that the mystery resistor might be the fix. I am going to send Szymon an email and ask what he used the resistor for (I will also ask what size) I'll let you know what he says.

It's a current limiting resistor for the LCD backlight LED. I used 220Ohm but this might vary depending on what LCD you use.