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  1. L

    Help with Prototype

    Just to provide you an estimation datapoint, I once designed and built a similar project using the CDP1802 microcontroller. It was a speech timer for the local Toast Masters club that would keep a countdown timer and flash green, yellow, and red warning lights at appropriate times. In addition...
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    Help: Oscilliscope Loading Circuit

    You have to measure at a low-impedance point in your circuit. That would be at the output terminal of the AD506 rather than at the input terminal. From your description, there is no way to measure the input signal directly because the source is high-impedance. I think you can put a load on...
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    Capacitor discharge

    Even though there is no accurate time=0 where Vo=max, any point on an exponential curve can be treated as time=0 where Vo=whatever V is at that point on the curve. No matter where you place time=0, it always takes one time constant to lose 63% of Vo. Of course when you are working farther down...
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    Building a pH meter

    In the article "Building the Simplest Possible pH Meter" http://www.66pacific.com/ph/simplest_ph.aspx it stresses the importance of using a high impedance input amplifier such as the TL082. Could your problem stem from your choice of the 741 op-amp?
  5. L

    Capacitor discharge

    Could you explain how a timescale of 50 hours in the first graph comes to be represented by a timescale of 500 seconds in the second graph?
  6. L

    0-99 Counter

    The internal RCO of the '163 only works for the binary mode. To run the '163 in decade mode you will have to use logic gates to generate the RCO the same way it is done for the '160 decade counter. Then use your generated RCO in the usual fashion. But also use the generated RCO to drive the...
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    Alternative to state machines question

    Suppose the price of some of the selections were to change. How would you handle that with a state machine? Was your implementation of the state machine done in hard-wired logic? Could your logic be used with different configurations of vending machine with the specific behavior modified by...
  8. L

    How does an amplifier work?

    You might want to read this article, "How Do Transistors Work? NO, HOW DO THEY REALLY WORK?" http://amasci.com/amateur/transis.html The author does a good job explaining the concepts of diffusion current, minority carrier injection, and bulk recombination without getting too technical or...
  9. L

    Need advice on relay / switch

    While not totally off-the-shelf, what I would use is a DPDT relay driven by a Recycle Timer. The relay outer contacts would be wired in a cross-polarity configuration. Each of the two inner contacts would be wired to an electrode. So when the relay is idle the electrode polarity is +/- and...
  10. L

    Analysis of stable RC oscillator

    Three logic inverters in a series loop is a naturally unstable configuration that will oscillate at the highest frequency the gate propagation delay will allow. This circuit inserts an RC low-pass filter in the loop to increase one of the gate delays and reduce the loop oscillation frequency...
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    How does an amplifier work?

    In the general sense amplification is a mathematical concept. If you analyze a transistor circuit, replacing the transistor with one of the useful transistor circuit models available, and derive the transfer function, the ratio Vo/Vi, then it often happens that the dominant term in the transfer...
  12. L

    need major help please

    I don't know anything about shrimp hatching, but if the off time can be increased to 15 mins then a mechanical light or appliance timer might work. Not sure how a syringe might work. Can the power-on sequence turn on the air pump and operate the syringe at the same time...
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    Please help finding resistance !

    What are the standard assumptions you make about the transistor such as Vbe, the current gain, is the current gain high enough to ignore the base current? Then start with the voltage across Rc, given the collector current. Vce is given, so the voltage across Re is simple to find. Knowing the...
  14. L

    comparator hysterisis

    Another consideration is whether the opamp has rail-to-rail output. If not, then Vout_HI may only be 10.5 instead of 12.
  15. L

    Complex circuit resistance between any two points

    Have you tried Google "resistance lattice networks"? What I found is that analytical solutions are non-trivial. If you are just looking for a numerical answer, then SPICE would be a good method.
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    Make a latch (flip-flop) using two relays?

    Check out these sites: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1338590/ http://tams-www.informatik.uni-hamburg.de/applets/hades/webdemos/05-switched/20-relays/flipflop.html
  17. L

    Magnetic Rocket Altimeter Arming

    Can the 1.5 mA operating current be separated from the 5 A igniter circuit? If so then use a miniature reed relay to trigger a CMOS latch that will supply the operating current. Use a magnet to activate the relay before launch and then reset the latch when back on the ground.
  18. L

    Airsoft kill counter

    Try Google "tally counter". http://www.amazon.com/Reddington-Electronic-Tally-Counter/dp/B0019VH9S0/ref=tag_dpp_lp_edpp_ttl_ex I'm not sure whether your primary objective is the gift or the experience from designing and building the device.
  19. L

    basic inverting amplifier

    The reason that happens in the real world is usually opamp input offset voltage and input bias current. Perhaps the SPICE simulator in ORCAD is taking into account the imperfections of real-world opamps.
  20. L

    run a low voltage led(3volt) at higher voltage(12-18 volt)

    Look at the datasheet for your LED; it should have a V-I curve. The only possible operating points for the LED are on that curve. I can guarantee that a voltage of 12-18 volts at 450-500 mA is not on that curve. Of course, you can power the LED with 12-18 volts if you put in a series resistor...
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