Member Since: February 4, 2011

Country: United States





CNC, Electronics, Arduino

  • I only have one I2C line on the Pro Mini I'm using. Any ideas on how to have two of these on the same bus?

  • Has me wondering if I could make an adapter for my old HP 7450 plotter to hold the pen and draw detailed circuit boards on plain phenolic boards. Hhhhhmmmm....

  • The RoHS Directive DOES have a purpose...

  • Be advised that using the '8Hz' bootloader is going to result in some very slow programs!

  • Back in the good (bad?) old days when noise was a big problem (especially over lengthy cable runs that picked up interference), the parity bits were used to determine if the data was truly valid. One parity bit was usually sufficient and if "most" bits were a 1, then the parity bit would be high (if most bits were low then parity would be low). The problem was that if noise made the parity match what was expected (even with bad data bits) then it would be interpreted as a valid byte. The addition of the second parity bit as a check against the first helped (mostly) eliminate any false parity checks (chances were very low that noise would make both parity bits the same value). Again, this was back when shielded wiring was a luxury and a lot of serial communication took place over ribbon cable. Generally speaking, the "noisier" the line, the more parity and stop bits you used to make sure you were getting valid data.

    With that being said, since most data "back in the day" was transmitted at very low baud rates due to the high equipment costs and bad lines (75/110/300/600/1200 baud) it was expensive in terms of throughput to add all of these stop and parity bits (essentially "throwaway" bits if the data was indeed valid) since they could consume almost 1/3rd of the total bits sent. Hence the 8/N/1 (8 bits, No parity, 1 Start bit) over good quality lines since it allowed the most information to be "packed" into the smallest number of bits sent. Just a little history there.

    As Pete asked "Why would you choose Even or Odd Parity?" I actually had several occasions where the noise on the line (back in the day) would tend to spike either "Low or High" most of the time. Choosing a parity opposite of where the noise or spikes would tend to be would help eliminate a lot of bad frames - again, showing my age.

    Noise is generally not a problem now with well-shielded wiring but remember that the protocol does not determine the method of transfer. You can use the RS-232 (485, etc) protocol through IR, Radio, Optical Fiber or anything else you can think of (with its own set of "noise" so that should give some idea about the reason for all of this parity and start/stop bit discussion.

    And one last tidbit: The "while(!Serial.available())" in the arduino is just a check against a bit to indicate a full byte has been received into the buffer.

  • My Chinese isn't that good but it looks like the shaft diameter is .20". Is that correct? I'd like to use these to attache to the back of my stepper motor shafts on my CNC machine to use as a DRO (Digital Read Out) of the current position. They seem like they would be accurate for this purpose with 2.84 pulses per degree of rotation. Any thoughts from my fellow tinkerers? ;^)

  • Darned! That milk was Rank!

  • UPDATE 8/2/2011: Be aware that this version (45A) can handle up to the 51.8v without smoking the sensor itself, the voltage divider circuit will easily exceed 5 volts if you attempt to sample the higher voltage since, unlike the current, it WILL NOT scale the voltage down to a 3.3v level. In short, if you need to sample voltage from anything higher than 13.8v then you may want the 90A or 180A version instead which will correctly scale the higher voltage (at a slight loss of resolution).
    Arduino A/D inputs smoke quite nicely when you put high voltages into them 8/

  • If you are flying there yourself (as I would), the two closest General Aviation airports are:
    KBDU: Boulder Municipal Airport, KLMO Vance Brand Airport and KEIK Erie Municipal Airport all of which are within 15 miles of SparkFun.
    (be aware of high elevations, short landing strips and prairie dogs in the vicinity of runways though! I'm not sure about prairie dogs, but turtles crossing the runway on takeoff in Slidell, LA made strange popping noises and a rough ride!).
    KDEN Denver International Airport is the closest major airport, roughly 28 miles from Sparkfun.
    All of this from a boy in Houston, TX. And you thought all of us Texans rode cows! ;^)

  • When used with a regulated 12v power supply and a constant 1 amp draw it reads correctly, but when the power is bumped up to 30 volts at 1 amp, it goes off-scale high (1023). What gives? Is the product listing wrong here or is the datasheet? If I would have known only the 90 and 180amp versions could handle the higher voltage then I would have spent my $20 each on those x3

No public wish lists :(