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Rate my Talon SRX breakout (EagleCAD)
I made a little SRX Breakout board for our talons, as our ribbon cable to encoder cable solder joints were always a bit janky and heatshrink tumors bother me. I stuck some LEDs on the encoder A and B channels and the limit switches, so that you can tell if the encoders/switches are connected and functioning without software. While making this post, I think I just realized that I can make all my semiconductors the same by assuming high=false low=true, as the limit switches operate that way but the quad encoder might be that way too. I assumed low=false high=true for the encoder, but now I think it probably doesn't make a difference. Maybe I should look it up.
Schematic: http://i.imgur.com/9ICCHRE.png Board: http://i.imgur.com/4M2SVRO.png link to source files https://drive.google.com/drive/folde...EE?usp=sharing |
Re: Rate my Talon SRX breakout (EagleCAD)
Also the two holes on the end are for zip tying the cables down. Maybe I should have explained that earlier. You're supposed to solder whichever wires you require to the corresponding pads on the board, and then ziptie the wire bundle together at the end to take stress off of the solder joints.
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Re: Rate my Talon SRX breakout (EagleCAD)
This looks pretty solid in terms of functions, and I like the use of transistors for the LEDs and the like. However, the resistor for the quadrature LEDs should go after the transistor, or you'll short your encoder outputs to GND.
As a side note, EAGLE does have an "LED" part in the default libraries, so you don't need to use a diode. Also, try using 2.2k resistors for your leds intsead of 100 ohm. 100s will probably cause too much current for the led, and 2.2k makes it plenty bright for indication purposes. I love the limit switch LEDs. Optional pullup resistors are great. You might want to try one of those header bridge thingies to switch between 5v and 3.3v (possibly also for the pullup resistors). Solder bridges make it hard to change without a lot of hassle. The one major problem I have with this board is that it's far to large. You can easily cut this down half the size. If you switch to soldering in headers instead of using solder pads, you'll save some space that way. At the very least, you can put all the solder pads on the "bottom" layer (facing up IRL) to let you shrink things down. Use the "smash" tool to separate names and values of components on the board. That lets you put the names where you want them most visible, and you can delete that values; those don't need to be on the board. Have you tried pricing this out on Digikey? |
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I like the free-ness of solder bridges, but I think some of your concerns aren't too big. 115 made their own SRX breakouts a while back and we haven't ever experienced problems with headers bending, although we've certainly seen everything else. If you want to keep the solder tabs, then putting them all on the bottom and shrinking them will definitely save you space. The smashing suggestion was mainly if you wanted to focus on making this smaller. I always label my parts as a reference in Digikey, so when they arrive I just match up R1 with R1 and don't worry about values. Obviously it fits fine just as-is. That BOM sounds about right. Mouser is pretty expensive compared to Digikey, so if you go Digikey you should save a few quarters. The 0.05" pitch header is expensive no matter where you go (it might actually increase in price on Digikey). You seem to have a good handle on what you want from this design. I recommend OshPark for manufacturing for a variety of reasons like the .brd native uploads, free priority mail, and relatively low cost and high quality. |
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For your forward and reverse limit, you should have to pads to connect the switches to, both GND and signal. That way the user doesn't need to muck about with wires going to odd places or anything. |
Re: Rate my Talon SRX breakout (EagleCAD)
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Re: Rate my Talon SRX breakout (EagleCAD)
I just noticed this- do you have adequate clearance between vias on the 0.05" pitch header?
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Re: Rate my Talon SRX breakout (EagleCAD)
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On a somewhat related note, I was thinking about using some sort of epoxy or other goopy compound to seal all the parts on the board, particularly the .05" header, from metal chips and any other potential source of shorts. Know of anything that would be fairly easy to apply and non-conductive? |
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A low temp drying oven is the recommended way to cure this. |
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Re: Rate my Talon SRX breakout (EagleCAD)
I'm jumping in probably a bit late and I'm short on time, so sorry if you've already though through this.
Q1/Q2 should likely be a MOSFET, right? Otherwise any voltage applied to the encoder pins will be pulled hard down by the transistor. You could put a resistor in series with the gate, but that will require a constant current draw. We've been using latching molex connectors for quite a while and have liked them a lot. Consider connectors instead of soldering wires down. |
Re: Rate my Talon SRX breakout (EagleCAD)
2 Attachment(s)
Take a look at the attachments. This is what our team has used for the last two years.. They have worked great, keep our wiring in order and allows for easy trouble shooting and placement on the robot.
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