Let's Make Robots!

Boards & Boards (to get you bored) -- a log of homebrewed circuits coming to life...

I decided to make a blog to serve as a log for the boards I design and/or produce... well mostly because I can. So here it goes.

NOTE: Older boards at the bottom, newer at the top. So do bottom-up read if you're after a chronological perspective.

 

05 - Practice makes perfect (eventually) OR the h-bridgemania

Ok, so given that there's always room for improvement let me just keep designing boards, and I could use some more efficient ones, so I just refitted the TIP122/127 into a MJE2955/3055 one (incorporating also some physical constraints corrections) and also re-designed DanM's previously mentioned "perf-ed" schematics now into a prettier and tidier PCB design. Also, it was a good oportunity to train my double-sided PCB making skills.

At the time I'm writing this (Nov, 18th 2012) despite having improved my transfer/etching skill I'm still very bad at soldering. Most of my solder points are a mess or at most passable, in the sense that at least they allow current to pass. However, I found it way easier to make proper solder points on boardhouse made PCB... also, doing vias on DS homemade boards it's still a pain sometimes...

04 - Finally improving on (some) noticeable board design skills

Continually following the wisdom of PCB design virtuoso Bajdi I've learned on how to do design a ground plane into my board designs (while using Eagle). Also using his Bajduino328 board design as template I've designed a "simpleduino" now sporting extra features as: 3.3V vreg (my first used SMD part), nRF24l01+ header and voltage divider to gauge battery voltage levels. Since, this board is meant to be used on my hoovercraft project I'm currently calling it the "hooverduino" board. Also, this is the first Double Side board in that I actually performed a double sided transfer/etching procedure (if one does not count the silkscreen on the ATmega fusebit doctor as a DS board). In parallel, I've also designed a couple of motor drivers boards: a simple TIP120 unidirectional motor driver and a TIP122/127 H-Bridge. Alas, my ignorance regarding electronics led me build an H-bridge with a ~4V voltage drop and thus highly inefficient for my current endevour, but despite that the actual production of the PCB all went jolly fine with just some minor quirks.

03 - Refining my design skills (well... trying to) & improving on the transfer/etching technique execution

So to keep honing both my Eagle and transfer/etching skills I decided to design more boards. I've designed a board to use for the remote control of my third project. It ended up being sub-optimal in terms of design, and even had a auto-routing flaw (easily fixed with by the blue jumper) that I only picked up after populating the board with components. In parallel I've decided to also transfer/etch my first Eagle design (the mousebot board) since I had a leftover piece of copper clad board just the right size for it.

Note: On the third panel the board looks all gooey as if a caravan of slugs and snails had run across it because I'm using clear nail polish to protect the copper tracks from oxidation.

02 - Starting with designing my own boards

Given that I did not what to be locked only to freely available board designs, I decided to start learning on how to use Eagle CAD. Given that I had a breadboard setup to program my atmega328 chips with my (ebay bought) USBasp and I wanted to free up both wire jumpers and breadboard, I decided that designing a permanent board for this would be a simple project to start learning on how to use Eagle (I actually started with a mousebot PCB version design but ended up only etching it later on).

Note: The transfer/etching procedure of this board was actually done in parallel with the ATmega Fusebit Doctor board and the acquired experience led me to write up this walkthrough/tip.

01 - Moving on to homebrew PCB toner transfer + etching

Trying to move up the ladder, and using as an excuse a couple of atmega328p which were fusebit locked I decided to make try some etching a board. I got an already proved-to-work schematics and layout, the ATmega Fusebit Doctor and got to work. Perhaps I should have started with some simpler board layout, but what the heck... if I could do simple I could also do complicated.

It took me a while, and mild violence had to be applied to the board but I got it to work and thus fixed the couple of "bricked" ATmegas I had laying around.

00 - The begining

After my first fumbling with some breadboards, I needed to make things more permanent, and since I did not want to go via ready-made block (more expensive, going-through-the-paces-negating) way I started of by doing a couple of board on perf board for my first bot.

So they were a basic homemade *duino, the called "kariloyduino", but now I call it "firstduino".

Basically it sports the minimum components to make a *duino with an external xtal and has a basic 7805 vreg based supply.

And a board to house the motor driver chip (L293D) based on DanM's schematics.

For my second bot I've also used perf board for "housing" the circuit.

 

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

I've been only relying on the rosin from the solderwire... I guess I shouldn't have :/ So acquire a solder flux bottle and drip/pencil brush the areas to solder just before soldering? I know... I'm actually not eager for the arrival of December :/

or just get a piece of rosin resin and make your own flux by grinding the rosin into a dust and melt it in alcohol...

after you remove the boards form the coroding bath, give them a brush with scotch brite and apply the flox and tin all the copper traces...

soldering the parts will be way easier after that and you will never have traces that will come off the board, if you know what I mean...

I've already pondered using some tinning process for the traces. However, I did not like the search results I got. Either I did not understood the processes clearly or they are somewhat even messier than etching. Also another important thing is that they seem to use VERY TOXIC stuff for tinning (and I have very little storage space, poor ventilation an no dedicated space for messy stuff, I do my etching in my kitchen floor). So, If you happen to know a reasonable not that toxic tinning process for DIY PCBs by all means do share :)

Tinning process:

- make sure your newly etched PCB is dry and has the protective stuff used for keeping the etchant away from the copper removed

- use a fine grit sand paper or a "scotch brite" to make the copper shine 

- apply a thin coat of flux or rosin disolved in alcohol (or acetone? I don't remember exactly which one works)

- apply solder in small quantities and spread it in a thin layer over all copper traces

- wash the PCB with alcohol or acetone to clean the remaining flux or rosin

 

Instead of tinning, you can do a Solder Mask:

- clean the PCB like above

- apply small round boullets of auto-adhesive paper over the pads

- spray paint the board

- use an exacto knife to remove the boulets

- tin the pads using flux

 

Good luck!

P.S. I used to do this process in 1996 when I was in high school and was etching my own PCBs. Now I order them online, because I hate to do the vias manually, my time is worth more than the cost of the boards.

Well, I'd thought of individually tinning each copper trace before but that would only work for simpler designs and I guess I would mess it up anyway. What I was looking for initially regarding tinning process was some sort of process where you'd be able to dip the board or something in some tinning solution and tin would adhere selectively only to the copper traces. I haven't looked much into that because all the processes that seem to be like that would refer solutions that were quite toxic/unhealthy.

At first I was not understanding the Solder Mask process, but then a quick google image search for "solder mask diy" and it elucidated me. Seems like an appealing process that I must try sometime.

Regardless, now I've came to the conclusion that I should clean better my board in-between etching and soldering, both with "scotch brite" and flux.

And I completely agree on the vias, bridging top and bottom layer is fairly easy and painless, but for some components it's wicked troublesome. Anyway, I want to experiment with typical DIY processes and I'm working my skills up so that I can also send for factory produced PCBs, but still not everything is worth the shipping wait or even cost (for me). So, for now I'm just learning and practicing so that I can sort of streamline an homebrew PCB process that takes the shortest time possible.