CCS Embedded Ethernet board heat & LCD questions

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

I just got the CCS Embedded Development Board. The linear 5V regulator gets really hot. I know the ENC28J60 Ethernet controller is not a low power part by PIC standards, but I am not used to anything on my PIC PCBs getting this hot. It runs a simple LED blinking program so there are no gross power bus shorts or anything like that. Is this normal?

Also the Ethernet lessons use RS232 output, but I am not having luck with my USB-RS232 dongle, and my old PC with real RS232 ports just blew it's fan. I would like to use the LCD on the demo board instead. I tried just redirecting the serial like this:

// printf("\r\n\nCCS TCP/IP TUTORIAL 7A\r\n");
printf(lcd_putc, "CCS TCP/IP TUTORIAL 7A");

It compiles, so lcd_putc is defined, but nothing shows up on the screen. Has anyone used the LCD on this development board? What do I need to do to make it work?

Thanks
_________________
The search for better is endless. Instead simply find very good and get the job done.

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

newguy · Joined: 24 Jun 2004 Posts: 1907

One of our boards at work uses the ENC28J60 and the thing gets ridiculously hot, so what you're describing sounds normal. From memory, I think it draws something like 200-300 mA while transmitting...@ 5V supply, that = hot.

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi,

Based on my own ethernet designs using the ENC28J60, I can tell you that it is a power hog. I assume you are powering the board with a 12VDC wall wart PS? If you have a lower output voltage PS, you can use that and reduce the power dissipation of the regulator. The dissipation is proportional to the voltage drop (Vin - 5V) times the current. You might also put a heat sink on the 7805 if the space on the board allows.

Do you have a schematic for the board? I can't imagine that the LCD interface is any thing more than plain vanilla, but you never know? Are you using LCD.c (from CCS), or Flex_LCD. c (from PCM)? Have you twiddled the contrast pot?

John

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

It is not the Ethernet controller that is drawing the power. The ENC28J60 runs off of a separate 9V -> 3.3V linear regulator that is just a bit warm. The 9V -> 5V LM7805 just runs the PIC18F4620 (10MHz XTAL 4X PLL), MAX232 (no load), 256k EEPROM, and not much else. I removed the LCD display so it is out of the picture.

It surprises me the LM7805 is getting so hot (150F) while nothing else on the PCB is very warm at all. I guess the next step is to start cutting traces and measuring currents. I really don't have the time to ship it back to CCS for repair.

Doug
_________________
The search for better is endless. Instead simply find very good and get the job done.

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

asmallri, you are right! There is an error in the printed schematic. The input of the 3.3V regulator comes from the 5V bus, not the 9V bus. So all the Ethernet controller's 200mA is going through the 5V regulator as well as the 3.3V regulator. As a hardware guy that is the way I would tend to design this myself. Spread the pain over both regulators.

It doesn't help that the 9V wall wart is actually giving 11.5V under load. Now that I understand the problem I can intelligently choose:
1) Ignore the problem, just keep my fingers away from that hot regulator.
2) Put a bigger heat sink on the regulator.
3) Rummage through my stuff to find a wall wart that gives a lower voltage.

Thanks Guys!
_________________
The search for better is endless. Instead simply find very good and get the job done.