Wednesday, February 25, 2009
Wednesday, February 25, 2009
I am learning about serial communication. Baud rate is the rate of transfer (bits per second). Data is transferred one bit at a time in "packets". A packet consists of a start bit, a stop bit, the data bits, and sometimes a parity bit. The receiving device and transmitting device must have the same settings (baud rate, # data bits, etc.) to successfully send data back and forth.
Friday, February 6, 2009
Friday, February 6, 2009
Learned all about transistors and "NPN open-collector ouputs"!
Transistors consist of a base, emitter, and collector. When no current is applied through the base to the emitter, no current flows from the collector to the emitter. However, when current does flow through the base to the emitter, a proportional amount of current flows from the collector to the emitter. The relationship is: Ib = B*Ic.
So... a little base current allows a much larger collector current to flow. (B approx = 100). Oftentimes, Ic can only go so high (depending on its source power). Thus, even if Ib is very high and via the relationship Ic should be huge, Ic will only go as high as it can based on the circuit its hooked up to.
NPN open-collector output:
Now, take the idea of a transistor and put it at the output of some circuit. More specifically, connect the circuit output up the the transistor "base", connect ground to the "emitter", and leave the collector open (hence open-collector output). Now, you have a connection (the collector) that is either a short circuit or an open circuit, depending on whether the base is receiving current from the circuit.
Use this feature to hook up any other circuit you want to the collector, without worrying about affecting the internal circuit!
NPN vs PNP: these are two types of transistors. They differ in that a NPN is typically closed unless a current is applied to "base", where as PNP is open unless a current is applied to "base"
Transistors consist of a base, emitter, and collector. When no current is applied through the base to the emitter, no current flows from the collector to the emitter. However, when current does flow through the base to the emitter, a proportional amount of current flows from the collector to the emitter. The relationship is: Ib = B*Ic.
So... a little base current allows a much larger collector current to flow. (B approx = 100). Oftentimes, Ic can only go so high (depending on its source power). Thus, even if Ib is very high and via the relationship Ic should be huge, Ic will only go as high as it can based on the circuit its hooked up to.
NPN open-collector output:
Now, take the idea of a transistor and put it at the output of some circuit. More specifically, connect the circuit output up the the transistor "base", connect ground to the "emitter", and leave the collector open (hence open-collector output). Now, you have a connection (the collector) that is either a short circuit or an open circuit, depending on whether the base is receiving current from the circuit.
Use this feature to hook up any other circuit you want to the collector, without worrying about affecting the internal circuit!
NPN vs PNP: these are two types of transistors. They differ in that a NPN is typically closed unless a current is applied to "base", where as PNP is open unless a current is applied to "base"
Tuesday, February 3, 2009
Tuesdsay, February 3, 2009
Learned a lot about dB and octaves. First, for Power ratios, the definition for dB is 10log(P1/P0)...NOT 20!! That is only for amplitudes!! Also, when finding points for a PSD based off of a spec which specifies slopes such as dB/oct, make sure that you are using the right reference number for your dB calculations!!!! The forward point is always the reference point... that is your reference amplitude and your reference frequency. If you have a spec which says 6 dB/oct, then that means that it is 6 dB per octave slope FROM THAT POINT!....that point is P0... not P1.
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