Hacking Circuits Together Using Existing Schematics

Question

I am working on a prototype using existing breakout boards from open source hardware manufacturers (Sparkfun, Adafruit, Teensy etc...). Everything is going great!

I am at the stage where I'd like to start designing my own PCB in order to consolidate the components into a single board.

Right now, each breakout board is powered by the same LiPo battery, so it seems that I might be able to simply use the existing schematics from each board and simply combine them onto a single board, where each "component group" draws its power from the battery and shares the ground... analogous to the manner in which the individual breakout boards are currently wired up.

Is this as simple as it seems, and is it common practice for beginning circuit builders to take this approach without implementing KVL, KCL, and Thevenin node calculations, etc...

Thanks for any advice on this.

Answer 1

There's nothing wrong with that basic approach. Chances are the PCBs that you are using were themselves adapted from typical application circuits for each of the parts.

Speaking of which, I think it's better to look up (and read and understand) the datasheets for each the parts before you blindly transfer the schematics to your own board. You'll have to find exact part numbers, pick packages and so on anyway. The components and the schematics may not include enough information even to just purchase new parts.

Answer 2

Yes, you can probably do what you want. You copy the circuits, but tie the power of each together and use a common ground. As you say, that's basically how you have them wired now.

A few things to watch out for:

1. Make sure the battery can still handle the current required of all the circuits together.

2. Think about the resulting ground currents carefully. By putting the circuits together, there is more opportunity for one to make noise that will be a problem for another.

3. You may need more capacitance on the overall supply. The supply is a obvious path for noise from one circuit feeding into another. Extra capacitance on the supply will help. You may also need to do more local filtering.

Answer 3

With the caveat that you've not mentioned at all what set of COTS dev boards you've put together, so this reply is equally general: If you're taking proven dev boards & their schematics, and you've successfully glued them together to do what you need, then yes, it is as simple as amalgamating them onto the one schematic and PCB, and perhaps even stripping out bits you don't need (ideally tested on the dev boards).

Doubtless there is still much that can go wrong and learning to be had, but that's expected, right? :)

Answer 4

Yeah, if you hook them up on the bench then you can just do the same thing on a PCB and combine all of the circuits. One thing to pay attention to when combining circuits since most of them are IC's nowadays is voltage levels and inputs. You can find the digital levels in the datasheet of the IC's. With digital circuits you need to make sure the logic levels "match up". A 5V CMOS output is not necessarily compatible with LVTTL. With digital circuits pay attention to the switching levels and currents. If you are trying to drive multiple inputs with an output then you need to worry about the current that the digital output can source to each digital input (if its too much it won't switch on all the way). Its a good idea just to get familiar with logic levels and input and output impedances. This is a simplification but if you don't understand start googling some of this stuff (logic level, fanout ect).