[Robotgroup] Printing PCBs

[Clendon Gibson]

Ok,

I now have multiple offers to help with cutting and drilling the etched boards. I am working out swaps with them for the favor of their time and effort. 

Now the only thing holding me back is the need for pledges to cover the cost of the photo-etch gear. So I am going to get a definite number for the price from Frys. As a ballpark I am thinking $10 for a drilled cut and etched board. You would need to add the parts and solder. (Unless someone would care to exchange soldering time and expertise for something? Maybe brisket at Pok-e-Joes?) 

Now I know that you roboteers NEED a dual H-Bridge capable of driving 50V at 2A! Heck I am getting two, one to show and one to blow. 

If I can get pledges for 6 or 7 boards I will consider it worth my time, get the gear and make the boards.

----- Original Message ----
From: Gray Mack <gray_mack at yahoo.com>
To: The Robot Group Mailing List <robotgroup at puremagic.com>
Sent: Monday, May 7, 2007 11:25:02 AM
Subject: Re: [Robotgroup] Printing PCBs

I highly recommend the photo etch process, once you get the development process down the results are very good. It requires pre-sensitized boards.  Frys sells them for I think $13 for a 6x9 +$2 for double sided. You need a bottle of developer (maybe $10) and the development light kit (maybe $30). print the tracings onto a transparency. Expose the board to light with the transparency on it. Develop the board and wash it. Then it etches in ferric chloride just like any other trace resist etching.
I have a dremel press, the only thing I dont have is a way to cut the boards (best done after etching since you cant expose this kind of board to light before hand).
If you want to defray the costs I recommend getting a signup list of who wants the boards beforehand. Its hard to tell how many H-Bridges are needed by TRG folks.

My experience with this chip is that it will drive a 6v battery/motor from a 5v logic supply and run cordless screwdriver motors. I didnt try letting the battery sag down below that or stalling the motor outputs to see if it went over 2 amps or whatever the max was. To use the sense feedback on the chip you have to use a current shunt, I dont know if something like a fuse will work for this. Overall it seems like a good circuit to have laying around on your bench.

-Gray

----- Original Message ----
From: Clendon Gibson <bsandyman at yahoo.com>
To: Austin Robotgroup Mailing List <robotgroup at puremagic.com>
Sent: Monday, May 7, 2007 9:54:27 AM
Subject: [Robotgroup] Printing PCBs


I am thinking of getting the gear together to make single or maybe double sided PCB boards. The techniques I was taught back in the day was to use copper boards coated with photo-resist. It looks like I can get a complete kit of this including some starter boards for $70-$80. 

In particular I am wanting to make this board for the L298 dual H-Bridge:

http://www.dprg.org/projects/1998-04a/

I am thinking that if I can sell 7 or 8 of these boards to interested RG members for maybe $10 a piece I can cover my costs and provide a useful service to the group.

What I don't have is a drill press or a means of cutting the finished boards. So would anyone be willing to provide the drilling and cutting in return for a board or two, or some fee?

Of course some members may be happy to do the cutting and drilling themselves.

If there is interest please let me know. I would also be open to printing boards from anything you can print on a transparency.


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