SparkFun Forums

[Spork Schivago]

Like this, right? The 10K resistor R5 doesn't effect the resistance of the 16ohm resistor, R2, right? If not, I think this board is done now. Thanks!

[davep238]

You're right, R5 doesn't affect R2. You will need to solder R5 before R2 and the ICSP header because otherwise it will be difficult to solder R5 after those 2 parts are installed.

[Spork Schivago]

Thanks so much for the help and info! Originally, I tried putting the ICSP header over by where the text, "UV Exposure Timer" was because there was a good bit of room over there. It was just really hard to route the traces. I would of had to use a lot of VIAs or try and redo the other routes.

I'd like to eventually replace some of the through-hole components with SMD components. Like the transistors, the 10K trimmer resistor and some of the capacitors. I'm just not very good at calculating what wattage I need for the SMD components. For example, for R5, I picked an 1/8 watt 0805 package resistor. Could I of used a smaller package though without it getting too hot? Could I of went for a 1/16th watt SMD resistor there? I know this isn't the place to ask questions like that and I don't expect anyone to respond. It's just stuff I still need to work on and figure out.

I think I understand the circuit a bit. Voltage comes in from the power supply at the X1-1 and X1-2 connector. It goes through the bridge rectifier B1 (B80C800DIP) which converts it from AC (if we're using an AC power supply), otherwise, if I power it with DC, the polarity shouldn't matter. It uses 4 diodes. It then powers the IC1 7812 voltage regulator which in turn powers the IC2 7805 voltage regulator. 7805 produces 5 volts and powers the PIC on pin 14 and also powers the LCD screen on pin 2 and pin 15. Pin 2 on the header is for the LCD's VCC, Pin 15 is for the LCD's backlight. It also provides 5V to the POT, which in turn controls the resistance going to the CONTRAST net on the connector that goes to the LED. Looks like the voltage regulator IC2 (7805) also powers the speaker there.

[davep238]

Thanks so much for the help and info! Originally, I tried putting the ICSP header over by where the text, "UV Exposure Timer" was because there was a good bit of room over there. It was just really hard to route the traces. I would of had to use a lot of VIAs or try and redo the other routes.

I'd like to eventually replace some of the through-hole components with SMD components. Like the transistors, the 10K trimmer resistor and some of the capacitors. I'm just not very good at calculating what wattage I need for the SMD components. For example, for R5, I picked an 1/8 watt 0805 package resistor. Could I of used a smaller package though without it getting too hot? Could I of went for a 1/16th watt SMD resistor there? I know this isn't the place to ask questions like that and I don't expect anyone to respond. It's just stuff I still need to work on and figure out.

I think I understand the circuit a bit. Voltage comes in from the power supply at the X1-1 and X1-2 connector. It goes through the bridge rectifier B1 (B80C800DIP) which converts it from AC (if we're using an AC power supply), otherwise, if I power it with DC, the polarity shouldn't matter. It uses 4 diodes. It then powers the IC1 7812 voltage regulator which in turn powers the IC2 7805 voltage regulator. 7805 produces 5 volts and powers the PIC on pin 14 and also powers the LCD screen on pin 2 and pin 15. Pin 2 on the header is for the LCD's VCC, Pin 15 is for the LCD's backlight. It also provides 5V to the POT, which in turn controls the resistance going to the CONTRAST net on the connector that goes to the LED. Looks like the voltage regulator IC2 (7805) also powers the speaker there.

You're right how the circuit works. The 0805 resistor is an easy one to hand solder. You will need at least a 15 volt power supply because the 78xx regulators need at least 2.5 volts more than the output. I looked up the Omron G6RW relay and didn't find it in the Omron catalog. Instead, use the "G6RN-1 12DC" relay. An SMD equivalent of the BC547 is the BC847. The 100nF caps (through-hole) can be 50 volts, 100 volts is overkill. The 100nF caps can be replaced with SMDs. The 0805 package is a nice size to hand solder. Also, C4 is not needed, since it duplicates C3. If a 5 volt relay is used instead of the 12 volt relay, then the 7812 is not needed. I've attached a ZIP file of the schematic and PCB using SMD parts (except for R2) and 12 volt relays.

[Spork Schivago]

Wow! That's freaking awesome Dave! Thanks so much!!! The original schematic (in PDF format) showed he used a G6RW for the relays but when I ordered the kit, it actually came with two JS12N-K. I have the 15 volt power supply.

If I understand this correctly, the relays are what provides power to the UV LED boards. There's 12 of them, 100mm x 100mm each. Essentially, you daisy chain them together to get one big top board and one big bottom board, each 200mm wide by 600mm long. There's 32 LEDs per board. Do you think using a 5 volt relay would be enough?

I have a basic understanding of relays. They're essentially a switch, right? So a 5v relay can handle a maximum of 5 volts, right? I really appreciate all the help you've provided. It's great that I actually understand parts of the circuit. Still get a bit confused with the transistors and the relays though. I really struggle with transistors. I've read a lot about them but the documents are really confusing. They talk about holes and things like that. They talk about how they can be used as a switch or an amplifier. NPN, PNP, emitters, collectors, bases and all that stuff, just a bit confusing.

[Spork Schivago]

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.

[davep238]

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.

[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!

[davep238]

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.