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SparkFun Electronics will be closed on July 3rd, 2015 in observance of Independence Day. Any orders placed after 2:00pm MT on July 2nd will be shipped out after the weekend. Thanks!

PeterP

Member Since: March 29, 2007

Country: United States

  • For folks thinking about attaching a second load cell here’s some datasheet info on channel B. It is not quite as sensitive as channel A.

    Channel A differential input is designed to interface directly with a bridge sensor’s differential output. It can be programmed with a gain of 128 or 64. The large gains are needed to accommodate the small output signal from the sensor. When 5V supply is used at the AVDD pin, these gains correspond to a full-scale differential input voltage of ±20mV or ±40mV respectively.

    Channel B differential input has a fixed gain of 32. The full-scale input voltage range is ±80mV, when 5V supply is used at the AVDD pin.

  • I have to admit that instead of using these FTDI boards, I usually use a a Teensy 2.0 programmed as a USB to serial converter. Its a buck or so difference in price but then I can always build some smarts into the converter to suit my application.

  • Any plans for an HMC5983 breakout? The 250hz update rate would be nice! It is mostly the same pinout but don’t forget to run pin 6 to a solder pad so we can select SPI/I2C.

    Also check out the MLX90333 hall effect sensor. It does all the math internally tio implement a hall effect joystick.

  • I’ve been playing with one of these for a couple days and found some quirks. I’ve been using the Teensy for awhile so most of this is in comparison. This is using Arduino 1.0 with the SparkFun Pro Micro Driver. The board is identified as Leonardo.

    There is no easy way to enter the bootloader. You have to connect the VCC to the adjacent RST pin. This connection needs to be maintained the entire time the bootloader is operational. If you disconnect the pin, the device immediately disconnects from the host. This is very annoying if board is not on a breadboard and doubly so if you already have a wire soldered to the VCC hole. I’m going to have to wire in a switch or something.

    The Teensy has a an on-board momentary switch that you press to enter the bootloader. There is no requirement that the switch remain pressed the entire time.

    I also attempted to convert my board to 3.3V operation by clearing the jumper next to the micro USB port. No luck. The voltage regulator doesn’t turn on and no power can be detected past the regulator.

  • The MAX1555 gets very hot when charging a 700mah single cell li-ion battery through the barrel connector off a 6V unregulated power supply (6.7V nominal). I have smoked two MAX1555s in this manner.
    Powering the board off the USB input solves the problem. I’m now charging off a 5V regulated USB supply. It takes a bit longer to fully charge, but at least I don’t have to worry about it bursting into flames.

  • Maybe I’m missing something but those current sensing resistors appear to be a bit undersized. At a continuous 2A drive the power dissipated by each pair of 1 ohm resistors is (2A ^2) * 0.5 ohms = 2W. Each resistor should be rated for at least 1 watt.
    I think the sensing resistors are above the Atmega and they appear to be 0603 packages. AFAIK, 0603’s tend to dissipate between 0.1W to 0.25W.
    Assuming a 0.25W resistor the maximum current drive is sqrt(0.25W / 0.5 ohms) = continuous 0.71A max per channel. Or about a 35% duty cycle at 2A.

  • These batteries are small, but not nearly as light as mentioned in the description. They are actually about 3g each.

No public wish lists :(