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PCB layers, parts sizes

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israa.adaam 7 years ago

Hi This is my first time doing a PCB and I'd like to confirm a few things: 1-How do i know how many layers should I have? I built my circuit in the schematic view then updated my pcb view without specifying any layers, is that okay? 2- When I placed pin headers I used the Phoenix 2 pin ones, what is their size in reality? will my wires fit there (simple thin wires)? 3- My circuit has LM741 op amps (DIP8) packaging, how do we mount them when the bard is printed? is it okay to solder 8 pin ic sockets then place my op amps? 4- Finally, one of my IC's is DIL08 packaged, how is that different than the DIP8 packaging (I wanted it in SMD or DIP8 but I couldn't find the part) Here is the link to my project: https://easyeda.com/editor#id=6f6122d087a646e1afcb60dd3e7202e1|81b85f4f03484ce5aaf2cb4a7e4a8ff5 Thanks

Comments

andyfierman 7 years ago

Hi, Welcome to EasyEDA. Your project is private so the link does not open anything. Please see: https://easyeda.com/Doc/Tutorial/share.htm#Sharing

israa.adaam 7 years ago

Hi, I just fixed it, here is the link: https://easyeda.com/israa.adaam/try2-fbd776a1cb344d9cadf6c08e4a03353d

andyfierman 7 years ago

Please do not be discouraged by this reply but you have made several mistakes in your circuit design and in the PCB layout which will mean that if you try to build the circuit on the PCB in their present state of design, your circuit will almost certainly not work. At present I do not have the time to explain everything you must do to correct these errors but I suggest that in the meanwhile, you study as much as you can things like the data sheet, applications notes and reference designs (which should include a recommended PCB layout) for the AD620. Please also try to find some sites that cover some of the basic rules of PCB design.

israa.adaam 7 years ago

Hello I did some research and here is what I did: I placed cpacitors near all the supply voltages to get stable supply with reduced DC elements. I also placed the RG as close as possible to the amplifiers. I changed the layout so that the elements releated to each amplifier are closer to it. Here is the link to my modified circuit: https://easyeda.com/israa.adaam/AD620_DS2-3f01a853e4fd41f9ab4620b0054695d1 Please notify me if this is better, I don't want all this work to be for nothing at the end. Thanks

andyfierman 7 years ago

Sorry but it will be a week or two before I can properly advise on your design. In the meanwhile, look for guidelines on power supply and ground routing for high gain/bandwidth amplifiers. Also look up into on the use of ground and supply planes. You do not need to go to more than the EasyEDA default of 2 layers but have a look at the Tesseract and the Uberclamp projects to see how ground and power areas can be added to a 2 layer PCB to reduce supply impedances.

israa.adaam 7 years ago

I'm afraid my time is limited and I have to submit this soon. I've done more research on what you said, and this link:http://electronics.stackexchange.com/questions/49821/routing-12v-and-12v-for-audio-opamps shows that there may be no need for ground and supply reouting if decoupling capacitors were used. "A local bypass cap is a low impedance shunt, thereby locally bringing the impedance back down." Is that accurate, and can I admit that in m design?

andyfierman 7 years ago

Basically, decouple every supply pi on every IC and make the supply and ground routing as wide as possible. Keep components close to the relevant IC and keep input and output traces separate.

israa.adaam 7 years ago

Yes I did that, but what do you mean by "keep input and output traces separate." 2 of my ICs have GND pins do I decouple the grounds as well?

andyfierman 7 years ago

You decouple supply pins to ground so if you have 2 supplies VCC and VEE then you add a cap from VCC to ground and one from VEE to ground. Try to keep output traces away from input traces to minimise crosstalk and the risk of unwanted feedback.

israa.adaam 7 years ago

Yes I've done all of that, I'll share the link as soon as I'm done arranging things

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