5 Replies Latest reply on Oct 15, 2018 10:16 AM by mcb1

    Beginner PCB design for LED clock

    pcbgogo_dph

      Hi everyone,

       

      I'm designing an LED clock using an Arduino, 74HC595s for the control, and ULN2803s for grounding the LEDs.

       

      I've got everything working on a breadboard, designed on a schematic and a first version laid out on a pcb in Eagle. I've never designed a pcb before,Usually,PCBGOGO helps me complete the design and production so I'm sure there's lots of little errors.

       

      The main question I have is related to decoupling capacitors and a ground plane. I was having trouble finding out online if the capacitors should have their own pathway to the 74HC595s, or if they could both simply be connected to the ground plane.

       

      I haven't put the ground plane in in this version, and any suggestions overall are much appreciated.

       

      Thanks for any help.

       

      Schematic:https://ffsmultimedia.com/eagle/clock-sch-v1.png

      PCB:http://ffsmultimedia.com/eagle/clock-brd-v1.png

        • Re: Beginner PCB design for LED clock
          Fred27

          The paths between the decoupling capacitors and the IC power pins should be kept as short as possible. It's also good practice (and often easier) to use a ground plane. Stick a polygon on one side, name it GND and agree to connect nets. Then when you click "ratsnest" it should show up as a filled copper pour. You will probably get away with a design with out these, but they help.

           

          Another tip for your first PCB is to plan a little for mistakes. Add test points for probing. If you suspect you might end up having one part of your circuit correct but a mistake in another part, think about traces you could cut to separate them and help debugging. I suppose what I'm saying is plan for it to be a V1.0 that could help you perfect v2.0. For instance my first PCB was a USB-enabled microcontroller and an NFC reader. I made sure the SPI connection between the two would be easy to cut. If I messed up the microcontroller or USB, I could then at least verify my NFC reader design by connecting it to a dev board. If the NFC was a disaster, I could at least check whether I got the USB stuff correct.

           

          I get a 404 on the schematic by the way. The link should be http, not https.

          5 of 5 people found this helpful
            • Re: Beginner PCB design for LED clock
              14rhb

              Apart from the electrical aspects, I also make sure I use copper pour when making my own PCBs to save on etcher. The flip-side is that I need to use more toner in my artwork. That didn't use to be a problem as I visited Staples and they printed them off on acetate for 50p - since Staples have now gone I am using my own laser printer and toner cartridges

               

              Rod

              3 of 3 people found this helpful
            • Re: Beginner PCB design for LED clock
              rusgray

              Some thoughts on your PCB design:

               

              -You should be using a ground plane, and with the simplicity of your board, probably at least a partial power plane.

              -Your current power distribution strategy (daisy-chain) is inefficient, and may cause a problematic supply drop near the  last LEDs in the chain. Use much larger traces for power routing, or better yet, use a partial power plane.

              -Those little loops near U1, U2, and U3 are going to behave like inductors. I'd recommend cleaning up the routing to remove unnecessary loops.

              -Your schematic does not have values filled in for all the passive components.

              3 of 3 people found this helpful
              • Re: Beginner PCB design for LED clock
                michaelkellett

                Adding to Russel's comments, all your tracks look too thin - I'm guessing from the picture at about 0.15mm (0.006").

                Apart from where you thread tracks between IC pins you could go much thicker maybe to 0.3mm or even more.

                This circuit isn't going to go very fats so it would probably work OK as it is but it's worth getting into good habits.

                Ground plane and thick power tracks are a good idea - I would use at least 1mm for the main power rail to the LEDs.

                It's usually best to route a board (if hand routing using one layer for vertical and the other for horizontal.

                Once you have routed you may be able to reduce the via count by breaking the rule a bit.

                I would advise against running tracks between IC pins unless you really need to  - why - because it means you are relying on good solder resist between the pins and the track and that will increase the cost of the board.

                 

                MK

                3 of 3 people found this helpful
                  • Re: Beginner PCB design for LED clock
                    mcb1
                    I would advise against running tracks between IC pins unless you really need to  - why - because it means you are relying on good solder resist between the pins and the track and that will increase the cost of the board.

                    I was looking at the tracks running between the connector pins on the Analogue/supply side and thinking exactly the same.

                    With some careful re-routing and a few using the top side it should be easy to shift the 7 tracks to avoid trying to run them though a large pad that is needed to hold the connector.

                    The alternative is remove these all together and just leave the Vin, two gnds, and 5v pin only on that side.

                     

                     

                    Cheers

                    Mark

                    1 of 1 people found this helpful