I like the idea of the
I like the idea of the resistor network, but that dip swtich does chew up some serious real estate. What if you changed it to jumper pins? If you need the room. Otherwise, it’s cool.
Reply doesn’t seem to work for me soooo…
@RBX I never thought of that angle, that makes sense. I will try and cram the 3.2mm holes back into the design. Thanks for the words of experience (again 
).
1) the comment about the switched power; did I rewire it to make more sense? I’m assuming you were noticing the motor supply was not controlled by the power switch. I changed things so it does now
2) RE: DIP switches… I was trying to make the resistor net more user friendly to turn on/off with the switches. It was an initial idea I had when I believed 2" square was much bigger than it really is. Now I know 2" is only 2" hehehe You’re absolutely correct about the huge footprint. I might try to substitute some headers in there to see if any useable room can be gained. I would only do it I think if I can accomodate the separate motor power supply. Can’t really think of anything else to add.
All the advice has been gold, thanks all.
Cramming more into that tiny
Cramming more into that tiny space…
What you can do is look for alternative packages for your parts. For instance, your power connector is horrizontal and big. You can use a polarized (keyed) Molex 2 pin connector from the SparkFun Eagle Library, like i used on my board. Heck, you can put 2 of them, back to back, one for logic and one for motors in the same footprint of your existing connector.
RE: Cramming / changes / battery option for motors query
Yes, that battery terminal is a beast. And so is that DIP switch. They have to go!
I’ve got a design I prefer that has a few changes:
- DIP switches replaced by bank of headers
- honking battery terminal replaced by 2-pin Molex (turns out the same as yours, RBX)
- Power switch now DPDT center-off. One pole gives 5V regulated, the other pole for power straight from the battery
- SN754410 can be disabled via a pair of jumper blocks
- Top layer has 5V power plane
- Overall design more finger-friendly
I gave the two battery option some thought but the ways to power the SN754410 increase. Should I have a switch for unregulated power and the second battery? Maybe it should have regulated power and the second battery. How about one for regulated/unregulated and then one for the first or the second battery? etc etc.
I personally don’t find the option for a second battery that useful but everyone seems to feel differently. That being said, I was looking for more opinions, this time about preferred power supply options. Maybe I can be swayed to squeeze something in.
I don’t like that DPDT
I don’t like that DPDT switch idea. Here’s why. If I have a 7.2V racing pack as my battery, and I accidently switch to power from battery, I now have 7.2V going to my microprocessor. Or did I misunderstand what you mean there?
I think you need to ensure you always have regulated power for the micro, since you have a power regulator on board.
I’ll reply here for Jax and
I’ll reply here for Jax and IG:
- you need 6V for servos, the motors and the regulator can work with higher voltages (or lower if needed, but so do servos)
- you can have a DPDT like you said, one pole sends power to the regulator and the other pole sends power to the motors, the input power can be from 2 different batteries
My suggestion is to have a separate power connector for servos. Then you can run the motors and regulator from a 2S LiPo (or more) and have a uBEC with the output set to 6V plugged into the servo power. This setup will keep everybody happy. Thinking more about this, I think it will be nice that after the power switch you can have a connector for the input of the uBEC and the output to the servo power connector. Why? to eliminate the need to have a power splitter and a separate switch for the uBEC. One flip and everything gets power. I mean it’s gonna be a small robot, not an airplane to flip 10 switches to power it up…
Yeah, what Ro-Bot-X said
Yeah, what Ro-Bot-X said about the power. A DPDT switch with unregulated power on one pole and power to the regulator on the other. One position is off (both battery and regulated) the other is on (both battery and regulated). Obvious, now that Ro-Bot-X points it out. It’s almost like he’s done this before…
Regarding power and the uBEC, let me see if I get this right. You can put a jumper after the power switch, on the line supplying power to the servos. If you leave the jumper in place, servos get batter power. If you remove the jumper and connect a uBEC, the battery power goes to the uBEC, and the uBEC’s output comes right back on the other pin to power the servos. Yes?
You still need to get ground to/from the uBEC as well. Gah. It works in my head. Quick! Resort to ASCII art!
Power to Servos-------- ------Power from Battery
Ground for Servos------ ------Ground from Battery
In the highly accurate diagram above, you have two options:
- Connect across the top two * * with a jumper to provide power to servos and the bottom two * * to provide ground to servos.
- Remove jumpers. A two-pin female header connects power and ground to uBEC from the two pins on the right. Another two pin female header provides output power and ground from the uBEC to the servos.
My cowgods, you guys are gonna pop my PCB!
I think I get what you guys are saying. It would be nice to have an option to use a second battery for both the motor supply and/or the servos. The sweetness of having both supplies turned on and off with one switch is an irrefutable thing. After RB-X spent some time pointing out my failures in v0.8 via Shout Box I think I can actually stuff this request in.
So I need to pack in another 2x2 header pin array, another battery connector, and I need to increase the footprint of the switch from the .20" wide SPDT you see to the .32" wide DPST upgrade that is needed. Plus the requisite schematic changes. I love the 2x2" challenge.
ASCII art \o/