5V wall worts and such...javascript:emoticon(':?:')

Talk about your replica, what you have done and what you use it for

5V wall worts and such...javascript:emoticon(':?:')

Postby foresmac » May Sun 07, 2006 9:16 am

I'm using a 5V 200mA wall wort, but I read somewhere that Vince recommends a 400-500mA one. Everything seems to work, but there is a problem that Vince attributed to bad RAM socket soldering or maybe a bad RAM chip. Would the would the 200mA max output be a problem? The wall wort is from my electrical engineering kit, and we use it for our ECE labs. Its output is a little noisy but all the chips have caps going into the Vcc pins as far as I can tell.

Also, I looked into get a different one form Radio Shack, but the ones they have are 4.5V or 6V.

From the looks of things the SE board uses a 9V supply and then a voltage regulator on the board. Is what I did dangerous for the Rev C board?
User avatar
foresmac
 
Posts: 16
Joined: Feb Mon 13, 2006 12:48 am

Postby foresmac » May Sun 07, 2006 9:30 am

OK, I lied about the wall wort. After closer examination, it can output 800mA. Where I got 200mA I have no idea. <shrug>

But still, is not using a voltage regulator a big problem?
User avatar
foresmac
 
Posts: 16
Joined: Feb Mon 13, 2006 12:48 am

Postby vbriel » May Sun 07, 2006 9:57 pm

Yes, here's why. If you were to take a raw voltage reading on the wall-wart you will see it output like 7-8 volts! The 5V will drop down under a load but is not a clean reliable power. 7805's with the 3 pins are easy to wire up and are cheap at about $.55. One pin gets the voltage in 6-12 (12 is really high and will cause the 7805 to heat up). The middle is ground and the other is 5V output. Connect a .22uF capacitor between the input and GND to clean things up and your are all set.

Too high a voltage can smoke some of the IC's, especially the 6502's as they are more likely to burn. The ATMEGA's are hearty beasts and probably won't take any damage from a light over voltage.
User avatar
vbriel
Site Admin
 
Posts: 1184
Joined: Jul Tue 19, 2005 1:10 pm
Location: Ohio

Postby foresmac » May Mon 08, 2006 4:13 am

Actually, this wall wort was used in all my ECE experiments, including my digital logic design class. We regularly used it with PLAs and 74xx chips. I measured the output with a DMM and got a consistant 5.16V output. I know from some op-amp experiements that the output can be somewhat noisy, and we usually put a .47µF cap in the power rails of our breadboards if the noise became problematic during the experiement.

After I get it back I'll troubleshoot the RAM problem we discussed. At that point I may get a different power supply and add the voltage regulator. Radio Shack has some 6V ones for pretty cheap.

Thanks!
User avatar
foresmac
 
Posts: 16
Joined: Feb Mon 13, 2006 12:48 am

Postby vbriel » May Mon 08, 2006 7:29 am

Some power supply wall bricks start off high and drop voltage as power is drawn. Yours does not sound like it does that. If you haven't had a problem with it, don't replace it. the cap is a great idea for the noise. Check your voltages at the IC's and as long as they are between 4-6V you are safe. The voltage regulator on the replica SE is so users can use their own power bricks. If they hook up polarity wrong, I installed a diode to block wrong direction. I need to make a silkscreen change and add the holes for switches and power.
User avatar
vbriel
Site Admin
 
Posts: 1184
Joined: Jul Tue 19, 2005 1:10 pm
Location: Ohio


Return to replica 1 General Discussion

Who is online

Users browsing this forum: No registered users and 3 guests

cron