Minerva

Member Since: January 6, 2010

Country: United States

  • Product DEV-12750 | about a week ago

    You can get the schematics here. http://repositorio.ipl.pt/bitstream/10400.21/3293/1/Disserta%C3%A7%C3%A3o.pdf

    The design is a little crude, and the results will probably be a lot noiser than they could be. This sort of biomedical instrumentation requires good analog design and layout, appropriate use of filters and appropriate power supply and ground design in order to get good results amplifying and acquiring these small, delicate signals without drowning them in noise. Significant improvements can probably be obtained with nearly negligible increases in existing BOM cost. Here are some idea and suggestions to think about.

    • All analog and digital power supplies and grounds should be separated. The designers have sort of recognised this a little bit, but it could be better.

    • There is not one single decoupling capacitor on the analog power supply in the EDA, ECG and EMG analog modules!!

    • Good filtering and decoupling on the analog Vcc rails to the analog stages should be used, with the separate analog power supply derived from the main power supply rail with LC filtering.

    • These sorts of systems often benefit from a narrow band-reject notch filter at 50Hz or 60Hz depending on country, to remove hum from the power grid.

    • I would probably use an external 12-bit ADC with a good independent voltage reference source, for example an MCP3208 connected to the microcontroller over SPI, rather than relying on the AVR’s internal 10-bit ADC and internal voltage reference.

    • I would use a star ground layout where the analog-side ground and the digital-side ground are only joined at one point, at the ADC.

  • Product DEV-11958 | about 9 months ago

    I don’t understand why the PCB layout is spaced out so wide. Basic EE literacy will tell you that a bypass capacitor should be as close to the IC’s power pin as is possible (and it wouldn’t hurt to put the MAX232’s charge pump capacitors closer either) but this is obviously not the case here. There seems to be a lot of unnecessary copper track length.

  • Product DEV-08786 | about 2 years ago

    Have you considered changing the boost converter to a more capable chip such as the LT1302, so you can get 500+ mA? It’s easy to hit the 150mA limit, say with an Arduino and an XBee Pro and a GPS and a few LEDs, and if you try and draw excessive current the boost converter voltage will drop off, potentially creating strange results that are hard to diagnose, especially for beginners.

  • Product COM-11155 | about 2 years ago

    This switch appears to have three terminals, from the photos.

    Therefore, I assume that it works just like your common sort of illuminated power switch of this type.

    Two of the terminals are silver, and one of them is gold.

    The gold one connects to ground, the first silver one connects to your 12V supply (or 5-12V, but not higher, because the resistor in series with the LED internally is designed for 12V) and the second silver terminal connects to your load +12V rail.

    Basically, the first two terminals are just connected to the SPST switch contacts, and the LED anode (and resistor) is connected to one side of the switch, with the LED cathode connected to the third terminal which you connect to ground. It’s gold plated so you know this is the “odd” terminal which is not connected to the switch.

  • Product SEN-10955 | about 2 years ago

    What are the pros or cons of this device relative to other digital-interface 3-axis accelerometer chips that are available?

  • Tutorial - (OLD) Accelerometer and Gyro Buying Guide | about 2 years ago

    I would love to see this updated to include comparison of some of the newer product lines such as the MMA8452 accelerometer. :)

  • Product SEN-09332 | about 2 years ago

    According to the datasheet, the positive acceleration-measurement is in the direction from the side of the chip with the notch on it, but on your board the silkscreen arrow appears to point the wrong way? Is that right?

  • Product KIT-10684 | about 3 years ago

    It should also be made more clear in the description of this product that a triac-based SSR does not work with a DC load, it will only work with an AC load.

  • Tutorial - Lessons from Rebuilding Illumitune | about 3 years ago

    I’m impressed to note that I’m not the only one who draws block-diagram documentation using the Eagle schematic editor :D

  • News - Another Friday New Produc… | about 3 years ago

    Personally, I don’t understand why Sparkfun stocks PICAXE products.
    My personal view is that PICAXE is garbage, and an Arduino-based system can do anything you can do with PICAXE, a hundred times better and more user-friendly.
    - Bootloader is proprietary closed software, you are locked into buying the pre-programmed PICs, and only the DIP ones are available.
    - IDE is proprietary closed software, and it’s Windows-only, so if you’re not a Windows user you’re not supported at all. There are no alternatives to using this IDE to program the devices; it’s not based on a standard open compiler toolchain (like avr-gcc, in the case of Arduino).
    - BASIC is a rubbish programming language, enough said.
    - Requires development board or a breadboard plus the PICAXE chip plus the programming cable to get started, compared to an Arduino which you just plug into USB and it just works.
    - The “official” programming cable requires an obsolete RS-232 port. However, I will admit that they have relatively recently resolved this by making USB cables available.
    - Power is not supplied through the programming cable, meaning that batteries always need to be used, even when using the USB programming cable.
    - There is nowhere even close to the same level of documentation and community support and openness and resources available compared to what you have with something like Arduino.

No public wish lists :(