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Member Since: April 6, 2013

Country: United States

  • Just FYI guys, when they say "no protection circuit" that includes undervoltage protection. I accidentally left one of these packs connected to a prototype and managed to discharge the entire pack down to 2.2V! The poor thing was so swollen it actually broke out of the black plastic they're wrapped in! It was seriously twice the size of a normal pack.

    I figured there was no fixing it, so I cut the cords off and properly disposed of it. I made the assumption there would be under-voltage protection at the very least; don't make my mistake! If you're planning to run these batteries raw on an Arduino or some other type of MCU, hook the output to a voltage divider and monitor it in software; once the battery hits 6V have your system turn everything off and go into the deepest sleep mode it can. This is the bare minimum I would recommend with these types of batteries.

    I'm now working on a nice little protection circuit that will monitor these packs with a chip from TI and then shutoff the output (via a FET) when the voltage gets too low.

    TL;DR: These packs have no under-voltage protection and can be discharged down to a point that permanently damages them. Be careful!

  • While an LM323T would work, it can drop down to 4.55V at full load; that's going to cause the RPi to reset the first time the motors stall out. A much better solution would be a UCC383T-5, which has an ultra low dropout of 0.45V@3A, so you can use a 7.2V Li-Ion pack; it's also got a minimum voltage of 4.85V at load, so no worries about the Pi staying up. It's pin compatible with the LM2940 and will function just fine with the RaspiRobot's input and output filters. You can even get one as a sample from TI, so there's really no reason not to give it a try.

  • Yes! Well, sort of... You'll need to get a 13x2 female header that has long enough pins as to allow a board to plug into it. I don't think the ones SparkFun sells (below in Related Products) will do the trick. What I ended up using was one of Adafruit's 13x2 Extra Tall Stacking Headers, which have 9.2mm long pins. They're designed to have a 1.2mm PCB stack on top of them, so the boards would't sit flush when I plugged them in; which I fixed by cutting 1.8mm off all the pins (making them all 7mm).

    Now I can keep my Pi safe and still keep the expansion boards on the outside, where I can actually work on them! It's funny, I've been searching for a case that would allow me to do this for quite awhile and it turns out the solution was one of (if not the) most inexpensive products on the market.

    Here's a quick collage showing the case and various boards installed (RaspyJuice RevA, PiFace Digital, Raspberry Icing and a AdaFruit Proto Pi Plate): https://twitter.com/TimothyBrown/status/328382662408564736

  • The software teachop linked (pi-blaster) is literally a fork of ServerBlaster... :)

    For the record, yes it works very nicely! I've done some tests using it to drive several motors with my own hardware and there's no interruption, even when I spike the CPU to nearly 100%!

  • I'm going to be working on that exact thing once mine arrives! I'll post an update letting you know how it's going. :)

  • Yes! The long single row header at the bottom of the board (GP0~GP25) gives you full access to all of the GPIO signal pins (3V3, 5V and GND are broken out elsewhere).

    I2C-1 will be pins GP0 (SDA) and GP1 (SCL). SPI has two uses on this board; you can either connect the appropriate GP pins to the A/D+D/A headers with a few jumpers, or you can use straps to connect the GPIO SPI pins to the ATmega328P which allows you to program it directly from the Arduino IDE or a patched version of avrdude.

    Basically, everything on this board is broken out and requires a bit of wiring to use. You can connect the 328P to the motor controller or buffers+switches+LEDs if you want. It's totally, 100% flexible, which makes it a pretty powerful prototyping tool! :)