Apr
1
Making CNC Stepper Motor Controller Printed Circuit Boards
By karlw
The stepper motor controller boards for my CNC router project are based on the L297 controller and L298 H-bridge driver combination. The circuit board design is the same as the schematic shown in the L297 datasheet. To keep the size of the boards small, I decided to make them double sided. I also needed to build a parallel port breakout board so I did that at the same time. The schematic and boards were laid out using EagleCad.
Click through for more…
The positive photo fabrication method was used to create the boards. The supplies are from MG Chemicals and are readily available at Sayal electronics. After the boards were designed, the top and bottom traces were printed onto transparencies in an inkjet printer. Because these boards are double sided, vias are used to connect the top layer traces to the bottom layer traces. The transparencies are cut to size and carefully aligned so that the vias on each side line up perfectly. I staple the transparencies together and then slide a double sided, pre sensitized, board in between.
The transparencies and the board are then sandwiched between two sheets of glass and held together with some paper clamps so that nothing can move out of place when the board is being exposed to ultraviolet light. The side opposite to the one that is being exposed to the UV is covered with light blocking plastic. when the top of the board is finished being exposed, it is covered with the blocking material and the other side is then exposed.
I happen to have a UV eraser unit left over from the ‘good old days’ of microcontroller programming and eprom erasing so I use that as my UV light source but a regular fluorescent bulb will also work. Note that I cover the entire unit up when it is operating so that I’m not exposed to UV.
After the board has been exposed it is developed much like a photograph. The areas that were exposed to the UV light are washed away and the circuit board pattern that is left will protect the copper from the etchant during the next step. This is where the whole process can get messy with chemicals. When Darin White completes his board mill we won’t have to deal with this any more.
What’s that cooking on the hot plate? That delicious black tar is ferric chloride, a metal etchant. The ferric chloride dissolves the unprotected copper from the board and leaves the circuit design intact. The solution gets darker as more copper gets dissolved and it takes longer to etch a board. I heat it up so that it is warm and then turn the hot plate off. This stuff has to be put back into the bottle and disposed of at a chemical waste drop off site when it gets saturated.
Etched boards washed and dried.
The boards are then drilled.
Here are two completed stepper motor controller boards attached to the parallel port breakout board. Note that the cables connecting the breakout board to each controller were fabbed out of an old hard drive ide cable by cutting the header on a band saw and splitting the ribbon cable. That saved me a lot of time soldering.
The Robots are coming.
By Karl Williams
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Hey Karl, great work and thanks for burning the boards for my mill too. Stapling the transparencies together for alignment is clever.
Go rapid prototyping!
DW
I’ve used that method, but I had trouble with the toner not being opaque enough, and having little pinholes in it.
One solution is to print two identical transparencies and stack them together.
I’ve also had success with a trick I don’t think anyone else has ever used. At office supply places you can buy a special effect foil that is used to add areas of shiny silver or gold to a laser-printed sheet, like for wedding invitations and stuff like that. It’s a thin plastic foil with a metalized layer on it. If you press them together with some heat, the metalization sticks to the toner. I used a laminator to roll them together.
The result is much more opaque. A few flecks of the metal sometimes stick in clear areas where they’re not wanted, but they can easily be cleaned up with a bit of scraping.
I wish there was a good way to do plated-through holes at home. Autorouting programs often make connections on the component-side of a board, under an IC socket. Without plating through, those connections don’t work.
You can get around the plated through-hole issue a bit by simply soldering the component on both sides of the board. In the case of a via, simply solder a short piece of wire from one side of the board to the other (I like to use lead clippings from resistors). But in some cases you can’t do that, like if the component body is pressed against the board preventing access.
In a case like that, you have to manually create a via that *is* accessible from both sides. A pain, but pretty much your only choice.
Interesting tip regarding the metal foil. I just double up my patterns like everyone else, or further blacken the pattern with a permanent marker. Is the foil method cost-effective?
out of the garbage. It’s got sort of a die that flattens a conductive insert that you jam in the drillouts. I’m going to try it on the boards Karl burned for me and let you know how it works. Probably easier to just solder components on both sides, as Jeff pointed out, but in the under-IC case you noted, this might work.
The kit is on the cart with my board mill if you want to check it out. Grey case.
DW
I was more worried about simplicity and effectiveness than cost. A package of the heat-transfer foil sheets is not very expensive.
And component pressed against the board is exactly the problem you have with IC sockets.
That depends on which sockets you get – some DIP sockets are elevated and have exposed, solderable pins on the component side.
good work
Hi
I’m trying to bulid a CNC and I’m using Mach3, I Searched the web alot to find schematics to the controller board but I couldn’t find any useful thing.
So, If you will, Send me the schematics that you used to bulid your CNC.
Thanks!
Can you mail schematics for the breakout board and drivers if possible
i like so much , can u send me pdf file of schematics and program of micro controllers and how to configure to pc to micro controller , plzz help me about this projects
what is bord spacification of using components and what program use in microcontroller and which software use to connect to pc and which one software use to working on this cnc ???
what the value of parallel port resistance ?????
merciiiiiiiiiiiiiiiiiiiiiiii
It seems to be a nice driver unit. I would like to know if you could send me schematics and part lists of those boards because I’m interested in building those circuits for a two axis lathe. Thanks.