Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

VGA output using PIC16F84

Status
Not open for further replies.

mdanh2002

Member
Hi,

I am trying PIC 16F84 Microcontroller VGA interface to create a simple VGA output on my LCD monitor. According to the website, if everything is wired correctly, the large digits "4:57" will appear on the screen. However, it does not work properly.

On the first LCD monitor (19 inch LG) that I tried, once the VGA output from the circuit is fed, the LCD switched from "Check signal cable" to a black screen, then quickly to "Power Saving Mode".

On the 2nd LCD monitor (14 inch Philips) that I tried, once everything is connected, the LCD switches from "Sleep Mode" to an apparently black screen. If I observe carefully, there is a circle in very dark gray color expanding in diameter from the center of the screen until it is big enough to fill the entire LCD. The circle will then disappear and the whole LCD is black, then it will appear and grow again. This happens at approximately once per second. I traced this behavior to the presence of the HSYNC and VSYNC signals. If either is not present, the monitor will be in sleep mode (e.g. no signal source detected). The RED signal does not have any effects on this behaviour.

I have checked with an oscilloscope and all signals appear to be valid VGA signals. I have tried to ground BLUE and RED but that did not help. I have tried also various values for the resistor (0 ohm, 10k, 90ohm, 180ohm) according to various other websites. Does anyone know what else I am missing on, or do I have to try on a CRT monitor?
 
Last edited:
Most monitors support ID on pins 11, 12 and 4. If one of these are not pulled low the monitor doesn't switch. You need to ground pin 11. (low res).

It would be a good idea to ground pin 5 (digital ground ) as well.

Cheers Ian
 
Thank you.

Got it working by ground all the suggested pins 5,11,12 and 4. But somehow it takes a lot of efforts to get the LCD display the test string (TECT), and not just "CHECK SIGNAL CABLE". I have to keep on disconnecting/reconnecting the ground, switching the RED/GREEN/BLUE wires randomly, or reset the PIC several times to get the LCD recognize it as VGA 640X480X60Hz. It just doesn't display it the moment the cable is connected. I guess perhaps the LCD is sensing something. Any ideas?
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top