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  1. L

    A little help from the pros

    RE NickS: How much base current do you think you will have?" The base current should not be more than 4 uA, so the voltage drop across the 47K resistor will be 0.2 V. Hope for 0.3 V drop across the Schottky diode and Vbe = 0.7 V max. That is just on the edge of working (or not working).
  2. L

    5V analog to 230V max

    The solution is simple in concept, but more tricky in practice to interconnect 5V DC logic to 230V AC power circuits. You will need a power triac thyristor to control the intensity of the lamps. You will need a zero-crossing detector to establish the phase timing of the 230V AC. Just read the...
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    A little help from the pros

    Without knowing full details of the timer, where I would start is the attached circuit. The signal voltage is very low for a discrete component design so this will be right on the edge between working and not. Use a Schottky diode to rectify the signal with a low forward voltage drop across...
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    A little help from the pros

    If that 1.2 V signal to the speaker produced a beeping sound in the speaker, then it is probably not a DC signal but a pulsed voltage modulated at the sound frequency and gated at the beep frequency. If that is the case, then you have a more interesting problem!
  5. L

    Small Signal Amplifier

    What I mean is that if you look at the 74LS162 datasheet you will see that for the interface to the counter clock input you need to pull down 3.2 mA and keep the low level input voltage within a few tenths of a volt above ground. An emitter follower is not going to do that.
  6. L

    Small Signal Amplifier

    It seems your problem would be the emitter follower that is used to drive the clock input of the 74LS162. The clock low-level input current is specified at -3.2 mA @ 0.4 V. The emitter follower resistor of 1K is not able to pull down the clock input. Drive the clock input with the open...
  7. L

    Inverting Op Amp

    Here's a thought experiment. Make the input resistor and feedback resistor an equal value. Make the input signal +5V, and assume the output is 0V. Then pin 2 will be at +2.5V. Now make the input signal 0V and assume the output is +5V. Then pin 2 will be at +2.5V. So put a constant +2.5V on...
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    Inverting Op Amp

    The first rule of operational amps is that they work to make the voltage difference between the inputs equal zero. So if one input is grounded, and a positive voltage is fed in through the input resistor, then a negative voltage would need to be fed in through the feedback resistor. But there...
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    ad7528 help

    Found a relevant passage in Analog Devices Application Note AN-318 under the heading AD7528 Single Supply Operation: Since you are using Vdd=+5V, you may need a low voltage opamp as a voltage follower with positive gain in order to buffer the 0.5V into the control transistors.
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    storage device for comparator output problem

    All I can think of would be a shift register, i.e., a string of flip-flops. Beyond that you would be looking at some form of RAM device. The shift register could be used for bit-to-byte or bit-to-word conversions, or a micro-controller used to stuff the bits into RAM.
  11. L

    ad7528 help

    The AD7528 datasheet claims that the differential nonlinearity is "Guaranteed Monotonic" over the full temperature range, yet the observed operation is not monotonic. Will a different AD7528 IC produce the same result?
  12. L

    storage device for comparator output problem

    Since the output of a comparator should be a digital logic level of 0 or 1, try a latch or a D-type flip-flop.
  13. L

    RS422 and RS485 using the same drivers

    As your referenced datasheet shows, an RS422 chip when equipped with tri-state outputs is essentially an RS485. An RS485 chip will work with an RS422 interface, but an RS422 will not work with a full RS485 interface where tri-state outputs are necessary because multiple transmitters are sharing...
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    Zener diodes for input protection

    OK, (*steve*) now you are speaking like a design engineer. I won't argue with that except to observe that sometimes, to an experimenter, a solution that barely works is indistinguishable from one that works very well.
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    Zener diodes for input protection

    Select the series resistor low enough to drive the parasitic capacitance on the input depending on your signal speed, and high enough to limit the maximum current through the diode. Your zener solution should also work, but using a Schottky diode is the standard practice. In fact, for analog...
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    Led Sequencer circuit help

    Not sure what the purpose of the 12v zener diodes would be. They all seem to be forward biased but a zener diode is only useful when it is reverse biased. Perhaps an ordinary rectifier diode would be more appropriate for your circuit. Are those yellow LEDs rated for 20 mA current? Are they...
  17. L

    Toggle switch keyboard emulator

    You need to search on the words "contact debounce". For instance: http://www.labbookpages.co.uk/electronics/debounce.html Interesting phenomenon that the charge and discharge cycles behave differently. But there are multiple proven methods for dealing with contact bounce. I would have...
  18. L

    Switching circuit

    Here is an example of how a comparator might be applicable for you. The LM393 has a open collector output and can directly drive the LED.
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    Switching circuit

    A comparator is not like a transistor in any way at all.
  20. L

    Switching circuit

    A comparator is an integrated circuit, similar to an operational amplifier, with two voltage sensing inputs (plus & minus) and a logic level output. Over a wide range of input voltage, if one input is a few mV higher than the other, then it sets the output to that logic level. For your...
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