Need Help with a 4 ea 5x7 LED Board purchased on eBay
Roy Carlson
Posts: 46
Hey Guys,
I hope I can get some help here.· I purchased a pcb kit and built a 4 ea 5 x 7 LED (red/green) display board with the marking on the PCB ALBAMatrix Display Rev 2.
I built the board and it seems to work the test routine which lights one column either red or green depending on the switch settings.
It uses a PIC 16F877 chip for the micro and 2 74HC245 surface mount chips for the communication to the leds.
I know this isn't an SX chip and I am sorry for asking here but I have seen several of the LED Matrix posts and thought someone may be able to help
me figure a way to use the board with the PIC or substitute and SX chip into the removable 40 pin socket.
I can be reached via·private·messages.
I have attached the two pdf's that came with the board when I built it.
Thanks in advance for any input.
Roy Carlson
PS - I have some experience with the basic stamp and have tried to learn the SX and PIC Basic but haven't touched the software since late last year.
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Post Edited (Roy Carlson) : 9/9/2009 2:53:01 PM GMT
I hope I can get some help here.· I purchased a pcb kit and built a 4 ea 5 x 7 LED (red/green) display board with the marking on the PCB ALBAMatrix Display Rev 2.
I built the board and it seems to work the test routine which lights one column either red or green depending on the switch settings.
It uses a PIC 16F877 chip for the micro and 2 74HC245 surface mount chips for the communication to the leds.
I know this isn't an SX chip and I am sorry for asking here but I have seen several of the LED Matrix posts and thought someone may be able to help
me figure a way to use the board with the PIC or substitute and SX chip into the removable 40 pin socket.
I can be reached via·private·messages.
I have attached the two pdf's that came with the board when I built it.
Thanks in advance for any input.
Roy Carlson
PS - I have some experience with the basic stamp and have tried to learn the SX and PIC Basic but haven't touched the software since late last year.
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Post Edited (Roy Carlson) : 9/9/2009 2:53:01 PM GMT
Comments
Do you have any other documentation with this PCB? It appears to be an I2C based display board which the SX28 / SX48 and probably the BS2 and certainly the Propeller can interface to. I dont really have a PIC background but·with more information on the layout and I2C format requirements for this board, we could probably get it to work with something from an SX chip·going to it in I2C format and an EEPROM.
My guess is that the PIC is an I2C interpretor chip as well as display driver for the 5x7 modules.·I would see if there is any more documentation on this first to see how to insert I2C signals from an SX chip into the already soldered board (PIC and everything in place).
If you have a schematic for the board that would also be helpful. Do you have the PIC processor on the board or are you asking on how an SX chip could be used in place of it?
Robert
I have seen several posting on the Parralax forums using basic software and tables to build the characters and then using look up tables and loop tables to move the characters across the display.
I dropped the project last year when I tried to get some help via the PIC Basic or MicroChip forums as everyone were insulted that I did not take the time to learn "C" and focus on first lighting LEDs before moving to the matrix.· I told them I had worked through several of the Basic Stamps in Class books and was trying to learn either the SX or PIC as an alternative to the more expensive basic stamps.· Once I mentioned that, I never received any more replies.
I do not have a schematic other than the pictures of the board.· If someone was interested and willing to play around with the board, I could Priority mail it to you.
My thoughts were to create something like the SX Medal that came with my SX Development Kit so that I can potentially use the message display as part of a Christmas display or on my train layout.· I am new to electronics, have programmed in the past (1980s) and have a passion for learning.· I work in the investment world as a financial planner so this is not my work, it is for my fun and to create things.
I have thought about taking an online course or going back to a trade school for electonics but my time is limited, I am 54 and work all the time.
Your help and ideas are very much appreciated.
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Here is the website: http://www.best-microcontroller-projects.com/led-dot-matrix-display.html
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·
As another low cost alternative, you might want to consider using a 0832 display from Sure Electronics. I have written SX code to display text and scroll data (still slowly working on scrolling text). From what I can tell, there is only SX code and Arduino code available on the web for these. Here is the link: http://forums.parallax.com/showthread.php?p=810347
These displays are only $8 each and you can cascade up to 4 of them. They are 32x8 resolution and your other PIC display board is 20x7. You·get more bang for you buck with them. I ordered 10 of the green ones (they also come in yellow and red) before I read you can only cascade 4. But I think with·more controllers or pins you can add more than 4 together.
Thoughts?
I received your board today and have troubleshooted it. I have attached datasheets for the 5x7 display and a suitable datasheet for the 74HC245. When applying power (batteries) when the PIC chip is socketed or not, the COLUMN 1 (pin 3) of the LTP1257 display (4th) is always on. SW2 can switch it between red and green columns. Since it was the entire row, it first led me to believe it may be a bad transistor. I took it out and tested and resoldered in a new one with the same effect. I then looked closer at the 2N3904 NPN transistors around them and compared voltages on the Collector, Base and Emitter. On the surrounding transistors the Bases had ~300 mV or roughly 0 vdc. However, on the Q4 Base (which the Emitter went to pin 3 {COLUMN 1} of the 4th LTP1257 display) it was reading about 3.8 volts and NOT about 0 volts like the other Emitters. Hmm.
After bringing up your PCB (PDF file you previously attached) and looking at Q4, on the bottom solder side you will see a trace from the Base going straight down which is then picked up on the component side and run sort of underneath R1 (140-150 ohms) and connected on 1 side of R1. This R1 connection is also run down and connected to pin 6 of the PIC chip. This may not be a problem because other adjacent transistor Bases had traces going directly into subsequent PIC pins. However, if we get back to the "other" side of R1, we see that it is connected to the Collector of Q6 which is also connected to all of the other transistor Collectors AND roughly 5 vdc as you might expect to see.
Here is where the problem lies. What is the purpose of R1? By connecting 1 side to the Collector of Q6 (as well as the other Collectors and 5vdc) it is dropping that 5 vdc across R1 and placing that 3.8 vdc on the PIC pin 6 as well as the Base of Q4 which then causes the Emitter to go positive to about 2.8 vdc across pin 3 {COLUMN 1} of the 4th LTP1257 display.
So If I un solder the R1 leg going to the Collector of Q6 it will take the 3.8 vdc off of the Base of Q4 thus not allowing it's Emitter to get to 2.8vdc and turning on Column 1. However, if this R1 resistor is removed as such then I see nothing on the display (whether the PIC is inserted or not). Perhaps this is how it is supposed to be as an I2C signal from JP2 maybe what excites this display. Who knows without more information and schematic. What puzzles me is why R1 is needed if the adjacent transistor Bases don't have a drop resistor going back to the PIC pins.
At this point, without more data to work with it will probably never be workable because we don't know enough about what the PIC is going to do. However, it may be possible to remove the PIC from it's ZIF socket and access the LTP1257 via the transistor Bases and conect an SX28 AND possible driving hardware to have a workable display. The 74HC245s have 2 functions. They act as buffers as well as also driver the Cathode rows on the LTP1257 displays. SW2 controls the /OE pin which switches the displays from green to red. I uses a similar technique using 74HC573's before to control red and green leds on a smiley face 16x16 bicolor clock (got published in Jan 2009 of Nuts and Volts magazine).
Summary - Unless you can provide me more data on what this display does (especially the purpose of R1), I recommend it be scrapped as a PIC project and possibly look into interfacing it to an SX28 through the PIC zif socket (to test) and later direct solder to the underside of the PIC once working. It may need additional drive components besides the sx28 but maybe not. I would need to look at all of the annode and cathode lines from the transistor bases and 74HC245 chips and see if they are all accessible from the PIC socket. If so, and there are no other problem resistor, capacitor, crystal, etc. interferences, then we should be good to go.
I will also mail you a couple of 0832 displays and make a solderless breadboard IDC connector for you if you wish. This may be the easiest approach (although it is only 1 color - in my case green LEDs) - but the work is already done by me.
Let me know how you would like me to proceed.
Tim
Hey Roy,
I encourage you to edit your original post to remove your email and phone number in an attempt to remain clear of spam lists.
Rich H
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The Servo Boss, a 12 channel servo tester kit from Gadget Gangster.
·····
Here is the info, Roy.··Nobody is permitted to submit articles to Nuts & Volts or any other publication.·
Instructions --
To Program a message:
1. Power on
2. Press S1 (letter A will appear)
3. Press S1 to increment letters and S2 to decrement
4. Find letter desired then press S3. Letter should flash (flash
means that it has been saved)
5. Repeat steps 3 & 4 to complete message (20 characters Max.)
6. Once message is completed then press S1 and hold then press
S2. A letter will appear (this is your program letter). You can
program up to 8 messages, these are named program letter
A – H.
7. Message will scroll across the screen.
To Delete a message:
1. Turn power on
2. Press S2
3. Use S1 & S2 to increment/decrement program letter
4. Locate the program letter (message) that you want to delete
then press S3 (program letter will flash).
5. Repeat steps 3 & 4 to delete more programs.
6. Turn power off
To Play a program/message:
1. Turn power on
2. Press S3 (letter A will appear)
3. Use S1 & S2 to increment/decrement program letter
4. Once program letter is located press S3 and hold then press S1 (program/message scrolls across the screen.
Notes:
1. Blank space is located after letter Z (it counts as a character
also)
2. If more than 8 programs are programmed, program A will be
overwritten and program letter will show as X.
3. Column 5 will flash when power is turn on (this is normal)
4. The reverse voltage diode D2 has been jumped to increment
brightness
The display board's PIC has not been programmed yet. Do you have the code for Roy to program it with or know where to get it from?
Attached, as a .TXT, is the program for it.· Same proviso as before, nobody is to submit articles to Nuts & Volts or any other publication based on the information made available here, in part or in whole, etc.
Do you have the capability to program in this code to the PIC? If so, I can send it back to you. If not then perhaps I can use this in figuring out how to write this into SX/B or at least the core.
PJ,
Thank you for submitting this code.
However, unless "you" wrote this code (and/or designed this product) or have documentation from the author to such, this is an open forum which allows all users to use the information as they wish. You do not have any authority on anyone else's work. Please stop with the disclaimer/proviso statement which some may view as leading towards paranoia.
The fallout you have had with me in the past needs to end as it shows signs of bullying and threat from my conversations with N&V. Can't we all just get along? Don't worry I'm not going to publish anything with this to any magazine but just going to help out a fellow SX enthusiast as we all should·with good intentions.
I expect everyone to have character enough to understand that.
Case closed.
I have decided to ignore PJ on the forum as not to offend him by using any of his contributions. I think this forum helps all of us to perform better as enthusiasts. By putting restrictions on anything contributed to this forum,·it makes the forum less useful. This should be all public domain information otherwise it should not be posted.
Tim Gilmore
It will be difficult to remember that the file "display.txt" has strings attached a few months down the line.
Rich H
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The Servo Boss, a 12 channel servo tester kit from Gadget Gangster.
The fact of the matter is, as has been explained a few times, this is not a "public domain" forum.· Everyone has the same "strings" whether stated explicitly or not.
The Propeller OBEX has even tighter controls.·
Hey, Roy, have fun, man.
My 'unreasonable' argument;
Suppose someone does not have a problem with the strings, a person who would not intentionally go against the authors wishes - how will they know what the author's terms are if they are not included in the file? You are trusting people to use your code only for certain purposes, why not help them to remember what those purposes are by including it in the file?
Today, this week, maybe for the rest of the month they will remember where the code came from but what about next year? My memory is not good enough to keep track of where every code snippet came from.
Rich H
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The Servo Boss, a 12 channel servo tester kit from Gadget Gangster.