VDD and VSS vs GND and +5V

Community PCB Design
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Wow, your traces look a lot nicer than my traces did! You did a great job there. Thank you so much! I have some questions though. What are the purposes of the round Via’s next to the SMD caps, C2, C3, C4 and C5? Also, I have a fancy soldering station now, a Weller (pronounced Veller) WX2 with a micro soldering iron so smaller SMD packages aren’t really a problem anymore. With that being said, is there a reason R2 is still a through hole resistor? It’s the 16 ohm one. Can that be replaced with an SMD type resistor, like R3, R4 and R5? Also, can I replace the diodes, D1 and D2 with something like this: http://www.digikey.com/product-detail/e … -ND/789335 It’s a SMD version of the through hole 1N4148 diode. I also have some hot air rework station made by Weller too. It’s an older model though. Still works great though. And does C1 still have to be through-hole or could I use something like this:

http://www.digikey.com/product-detail/e … -ND/396321

Also, for the trimmer potentiometer, I was thinking something like this:

http://www.digikey.com/product-detail/e … ND/1089395

The caps for the voltage regulators, they’re called filter caps, right? And their purpose is to just clean up the input and output going to and from the voltage regulators? Blocking AC and stuff like that, right? Would adding a fuse to the timer board be pointless if the power supply has one or would it be a good idea? I remember in college, when I was in a PC lab, the teacher asked me to get a PC working, for a challenge. I stripped it down, put it back together, and when I hit power, the motherboard started smoking. I believe the power supply broke and was throwing AC voltage at the board instead of DC. It was kind of cool but a bit embarrassing. I should’ve checked it with a PSU tester first. The teacher said he was glad I didn’t because it would of ruined his PSU tester but I think he was just trying to make me feel better.

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  1. You can use the SMD parts that you’ve chosen. The trick is finding them in the libraries. There is a SOD523 package in the diode library (diode.lbr). You can add this to the list of 1N4148 packages. When you have the 1N4148 device displayed you will see 2 packages in the right window. In the right window, select NEW and scroll down until you find SOD523. Click on that and then click on CONNECT. Connect Anode (A) to Anode and Cathode (c) to Cathode and click OK. Save the library and you’re done. In the board editor you will need to click on LIBRARY and then UPDATE to use the new package. Choose “diode.lbr” and double click.

  2. The spec’d relays have a 12V coil. The contacts are what is connected to the load, in your case LEDs. What I meant by a 5V relay is a relay with a 5V coil. The contacts are still the same and they can handle the LEDs with no problem.

  3. I left R2 as a through-hole part because I wasn’t sure of the current it needs to handle.

  4. The 100nF (0.1uF) caps are needed for the voltage regulators, mostly to keep them stable. Their outputs tend to oscillate without them.

  5. The GND vias are needed to connect the top and bottom GND planes. I used a 24mil (0.6mm) drill. With through hole parts the pad for the GND lead connected the 2 planes, so the vias weren’t needed.

  6. The transistors are there to drive the relay coils which require more current than the PIC can handle (a 5V relay needs more current than a 12V relay). So the transistors are used to boost the current. The diodes are there to handle the inductive kick back of the relay coils. Without them the transistors could be destroyed.

  7. If you use a 15V power supply you will be OK. However if the power supply puts out more than 25 volts, then C1 could be destroyed since it’s only rated for 25 volts.

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Wow, thank you. Extremely informative. I’m going to go back to learning more about circuit design for a bit. I still got a lot more to learn and stuff. Going to try and find a good on-line resource that covers a bunch of stuff. Someone on another forum posted a link to one a long time ago. Maybe I can find that. Thanks for all the help and stuff and when I get better at this stuff, I’ll be back to show ya what I’ve done!

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Spork Schivago:
Wow, thank you. Extremely informative. I’m going to go back to learning more about circuit design for a bit. I still got a lot more to learn and stuff. Going to try and find a good on-line resource that covers a bunch of stuff. Someone on another forum posted a link to one a long time ago. Maybe I can find that. Thanks for all the help and stuff and when I get better at this stuff, I’ll be back to show ya what I’ve done!

You're welcome for the help. I had fun. I look forward to seeing what you come up with.