Brian park

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Brian park

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  • 08.21.2008
  • It’s an electromagnetic-mechanical world
  • De-gausser won't work. It will "solve" the problem for awhile, until the parts re-magnetize from the earth's or other field. Better is to have some strong magnets waved over to ferret out parts that will magnetize. Even the head itself can magnetize (this was persistent problem in tape recorders), but in this case, it is no problem.
  • 04.27.2016
  • Control an FPGA bus without using the processor
  • About USB dongles on PCs: they are great except when they don't work, which is almost always! They fail to follow the PC protocol totally, and by Murphy's law, your application will demand it. Am example is the "break" code, which is staying in the "space" state for longer then 10 x baud period. Most dongles indicate "zero" for the byte so sent. Debuggers often use this code in the initialization as a preamble to the "security code" that must be sent. Go to the flea markets and scoop up those old PCs! Other dongles choose their baud rate seemingly randomly, including not even standard baud rates. Most often baud rate will be 2x or 1/2x rate set in PC (set by some random number table). This caused much consternations in expensive military program I worked on.
  • 10.28.2004
  • System implements digital-clock modulation
  • How do you prevent the loss of the 1 in the register if it is at position 20, about to loop around, and the "advance" command is given to feed 19 instead? Doesn't that cause the 1 to be lost?
  • 01.29.2017
  • What are magneto-inductive MEMS?
  • You use the word MEMS, which stands for MicroElectroMechanicalSystem. Where is the "mechanical"? This is totally electronic! Where does the bias magnetic field come from? From the earth's field? What if in a particular area the earth's field is zero, due to surrounding conditions? How is the presence of the car detected, is the field larger or smaller?
  • 12.19.2016
  • Proprietary AC/DC adapters: Good idea or nasty trick?
  • It is sleazy marketing. The first thing needed to be done is blowing Dallas semiconductor off the planet. They have been manufacturing ICs that prevent things from working, such as this and on printers, to "reject" perfectly working parts, and to prevent software from working. Secondly, Dallas makes those ICs with schemes more sleazy then their external intended function. For example, I sampled some Dallas programmable timer chips to use in military timers. The chips didn't work when put into my circuit, but worked in their "demo board". The reason they didn't work was they had an on-chip "R-C" reset circuit, which relied on the sudden application of the supply (with dV/dT being greater then a rather large value). This precluded using a bypass capacitor of any significant value on the DC supply line! This spec was not on the data sheet; it is only provided when you ask one of their engineers. I abandoned the IC, and want with reliable 4000 CMOS logic, which works properly, because the required reset lines are brought out. In addition, static susceptibility is well documented and tested. Both Dell and Dallas deserve to be blackballed over things like this. it is the only way products "made for the customer" will, in fact, be made for the customer. When suppliers learn that they won't be able to get away with this, they will stop doing it.
  • 12.14.2016
  • Real world RS-485: Low power, low EMI
  • The trouble with RS485 is that it claims to solve a "problem" with RS232 that it doesn't solve, and that "problem" is ground loops. RS-485 doesn't solve that problem because the true differential rejection is limited to the common-mode voltage range of the (usually) ICs, not true transformers. If "A" is one line, "B" the other, and "C" is the "ground", then the receiver IC "calculates" not A - B, but (A - C) - (B - C), which becomes invalid as soon as the common-mode range (only about 5 volts for most ICs) is exceeded. The better way is to use RS-232, and float the receiver on the ground line from the transmitter. You still have differential receiving, and the common mode is limited only by the circuit isolation in the receiver. In addition, one wire is saved in the configuration. this becomes significant when, for example, there are 4 RS-485 links, requiring 12 wires instead of 8.