PCB Prototyping - where to start?

Projects General Guidance
1

So, I'm interested in putting a bunch of different modules together on a single pcb that I can swap into my model trains. I've already attempted putting every module together manually, but there is just way too much wiring and unecessary crap to fit easily into an O gauge locomotive. I've managed to short quite a few things already.

This is the list of things I'd like to get onto a roughly 4"x2" board:
1: Max9744 amplifier - similar to this Overview | Adafruit 20W Stereo Audio Amplifier - MAX9744 | Adafruit Learning System without all of the unecessary ports and connectors.
2: NRF24l01 pa lna + 3.3v converter (so I can supply the board with 5V and not have to worry about another external converter)
3: Slots for a teensy 3.2 or LC to be mounted
4: SD card reader
5: Motor controller (can handle 13A 12Vdc) currently using cytron MD10C, but a basic H-bridge design would probably be fine, so this might be one of the easier things to put on the board
6. At least 3 mosfets for the control of a fan, smoke unit heating element, and smoke fluid pump

So, my main questions are:

  1. Is this even remotely possible, in your experience?
  2. What is a good software to use in designing such a board, with the easiest learning curve? (only one I even know of is OrCad, could probably get a copy through school).
  3. Are there companies out there who would put something like this together, or would I have to just print the pcb and solder all of the elements on myself?

Thank you guys, and of course any advice is appreciated. Just looking for a good place to start, I know there is a lot of information out there on the internet but its quite overwhelming... it would be nice to hear from someone who has had experience with this kind of thing.

2

There are soooo many threads about PCB design and PCB manufacturing on this forum.

Use the search function at the top of the page to review them.

.

3

I use Eagle. I consider it easy to learn. If you are starting from scratch then spend 30 minutes looking at KiCad too.

That seems like a lot for that size board. That is just one PCB? You may need 4 layers and that is a tough place to start. Maybe just start with 2 or 3 things with the Teensy. The boards are so cheap that you will only spend $20 and a couple of weeks to fix your first 5 screwups.

4

Sounds like a lot for that board - but it also depends on how much vertical space you have to place those components. For starters you'll have to go for SMD components where possible, otherwise it really won't work. I really doubt you need four layers, there's a lot you can do in two. I've done what sounds like at least this complex a circuit on a two-layer PCB with only a handful of traces on the back.

The 13A MOSFETs will have to be TO220 packages, with heat sink. Even at very low RDS(ON) you dissipate about 4W per MOSFET. That's going to take half of your board, and you need sufficient vertical space AND ventilation (as it'll be inside your train: a small fan).

The other three MOSFETs can be SOT-23 so don't take much space. No issue there. The connectors for your smoke, lights, etc will take more space.

SD card reader also takes a lot of space on your PCB, unless you take one on a separate breakout board and place it vertical. Remember to allow for space somewhere to take your SD card out.

Then the Teensy. No experience really with that board but can't you somehow ditch the board and just use the processor? That also saves a lot of space.

You'll also probably have to go double sided (components on both sides) and go for the smallest packages possible (and yes you can hand solder 0.65mm pitch VSSOP packages, it's quite easy actually). As you put your Teensy on a socket you'll have a lot of free space under it. Great for all kinds of surface mount components.

For software, I'm using KiCAD. Does the job well.

5

You can't take the processor off the Teensy board. The chip which makes the MK20D work like an Arduino is not available unless you buy the whole Teensy.

Yes, definitely space the Teensy up or put it on the back side so that components can go inside its footprint. I would not expect to put more than one or two components on the back side unless you are really slammed for space.

If you get a Teensy 3.5 or 3.6 then the SD card reader is included for free. It's the same width as the other Teensies but obviously a bit longer.

For a motor controller, the VNH7100 can handle up to 18A max and it's tiny. It's also very low RdsON so it won't heat up much. I've never used one before but I just got a bunch in the mail to try out for my next design. At 100milli-ohms it's not going to generate a lot of heat.

For switching general-purpose devices like a fan - including PWM control - I would go for a chip like the BTS716G. 4 outputs with RdsON of 140 milli-ohms. For high current, you can pair up channels or even all 4. BTS5012 is single-output but it handles more amps and has current feedback so you can see if your fan is drawing power.

For the audio amplifier, buying that Adafruit item as a pre-built module is going to save you a gigantic amount of time and effort. If you can mount that over the top of your 4"x2" board then it will be silly to try to copy that into your main PCB.

6

MorganS:
For a motor controller, the VNH7100 can handle up to 18A max and it's tiny. It's also very low RdsON so it won't heat up much. I've never used one before but I just got a bunch in the mail to try out for my next design. At 100milli-ohms it's not going to generate a lot of heat.

The problem is that the amps go cubed... 13A at 100 mOhm = 13x13x0.1 = 16.9W dissipation. That's a lot of heat to handle inside a small train body.

I was calculating at 20-25 mOhm RDS(ON) which some MOSFETs can do (but probably not the p-channel ones).

7

MorganS:
You can't take the processor off the Teensy board. The chip which makes the MK20D work like an Arduino is not available unless you buy the whole Teensy.

For the audio amplifier, buying that Adafruit item as a pre-built module is going to save you a gigantic amount of time and effort. If you can mount that over the top of your 4"x2" board then it will be silly to try to copy that into your main PCB.

Yea I just plan to mount the teensy to the pcb directly - the teensy is much too complicated.

wvmarle:
Sounds like a lot for that board - but it also depends on how much vertical space you have to place those components. For starters you'll have to go for SMD components where possible, otherwise it really won't work. I really doubt you need four layers, there's a lot you can do in two. I've done what sounds like at least this complex a circuit on a two-layer PCB with only a handful of traces on the back.

SD card reader also takes a lot of space on your PCB, unless you take one on a separate breakout board and place it vertical. Remember to allow for space somewhere to take your SD card out.

You'll also probably have to go double sided (components on both sides) and go for the smallest packages possible (and yes you can hand solder 0.65mm pitch VSSOP packages, it's quite easy actually). As you put your Teensy on a socket you'll have a lot of free space under it. Great for all kinds of surface mount components.

I think you're correct about doing this in two layers. But If I end up using the pre-built max 9744 board I may have to do 3. if each layer is no more than half an inch (including the pcb and components) this will probably be fine in most locomotives. I'd like it to work in future locomotives as well, ideally, so that's why I'm trying to go as small as possible.

I could probably save space by knocking those audio jacks off the max9744 and directly soldering to the board rather than using the force-fit screw in wire holders (or whatever they are called).

I might be able to go with the teensy LC or 3.2 and have a separate vertically mounted SD reader. This might actually be a better idea depending on the loco.

Also, the 13A for the motor controller is an absolute max. Its likely going to be much less than that unless the loco is pulling a long and heavy train. Right now, I measured the MD10C at 100 degrees F, so it does get quite toasty even at minimal loads (about 1-2 amps).

Anyhow, thank you everyone for all of the wonderful suggestions on modules! I'll definitely check out Eagle, I keep hearing thats all the rage. I managed to secure a copy of orCad as well, so might try that too.

Apologies for the late reply, have been dealing with school. Cheers!

8

+1 for using a Teensy 3.5. The cost difference is minimal between a 3.2 and the 3.5, you maintain 5 volt tolerant digital inputs (lost with the LC), the built-in micro SD card which has its own, dedicated SPI CS pin and it supports hardware floating point. Painless to use, fast as blazes and rock solid.

9

avr_fred:
+1 for using a Teensy 3.5. The cost difference is minimal between a 3.2 and the 3.5, you maintain 5 volt tolerant digital inputs (lost with the LC), the built-in micro SD card which has its own, dedicated SPI CS pin and it supports hardware floating point. Painless to use, fast as blazes and rock solid.

That is true. The 180 mHz is very noticeable...I built a lightsaber with neopixels and the teensy's processing time of that library was night and day over an 16mHz pro micro. The pro micro was just sluggish. It also helps with polyphonic audio I think...which is useful since playing different sounds on the loco (compressors, drain cocks, whistle, chuffing, etc.) making it a bit more realistic.

But yes, the 5v tolerant pins are nice...that way if something shorts with the dc/dc converter (which I think I forgot to mention, but am not worried about) then the board is fine.

I was thinking for the motor controller I could just use four of these: N-Channel MOSFET 60V 30A - COM-10213 - SparkFun Electronics in an h-bridge config like this: https://i.stack.imgur.com/s9Uvc.png

Each one can dissipate 75w with an operating temp range of -55 to +175C. From the sound of it, that would be fine, and four of those guys would take up less space than the MD10C.

10

snowskijunky:
I was thinking for the motor controller I could just use four of these: https://www.sparkfun.com/products/10213 in an h-bridge config like this: https://i.stack.imgur.com/s9Uvc.png

Each one can dissipate 75w with an operating temp range of -55 to +175C. From the sound of it, that would be fine, and four of those guys would take up less space than the MD10C.

Yes, but the drivers for 4 N-MOSFETs will take up more space. A motor driver IC will always take less space than the equivalent 4 MOSFETs. The only reason for using discrete devices is when your current or voltage is too high for the available ICs.