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  1. Merlin3189

    555 TIMER - Trigger Pin 2 Voltage??

    Your problem is that when the switch is open, pin 2 is not connected to anything. R1 in Rleo's circuit will fix this and is probably all you need to add. The rest is to convert a prolonged press into a short pulse. R1 connects pin 2 to the V+ rail and puts it at this Voltage. The switch can...
  2. Merlin3189

    How to increase 555 timer output voltage

    I'm not sure that helps. It still doesn't explain why the LED series resistors have a 2:1 ratio. A 2V drop from 12 to 10 or even 9 to 7 would not require a 2:1 ratio. I can only presume there is an unmentioned difference in the current required for each LED. Anyhow, if Peja requires 12V to...
  3. Merlin3189

    what happens if emitter-base & base-collector junctions are forward biased with 0.7V?

    I tend to agree with Dexterdev, I too have a doubt regarding what happens if both emitter-base & base-collector junctions are forward biased with 0.7V I remember with early transistors (OC70 type) it was ok to reverse the emitter and collecter. The gain was usually lower, but they worked...
  4. Merlin3189

    Delta - Wye transform help

    Yes. Intuitively, the circuit is symmetric, so the potential at junction R1-R2 is always the same as at junction V1-V2. If the potential at both ends of R3 is the same, there is no PD so no current. You could therefore replace it with any passive circuit, but an open circuit is the most...
  5. Merlin3189

    555 Timer Circuit

    The 555 was a wonderfully versatile chip. A search on the internet or in amateur electronics books should quickly find you 100's of circuits and explanations of their operation. The question you raise is a common one and has several well known solutions. Your circuit will give a pretty good...
  6. Merlin3189

    electrical interference

    I have a problem with interference to my audio system when using my laptop. I believe that it originates in the PSU as it does not occur when running on battery, even when the laptop audio is connected to the system and the PSU is plugged in but switched off. I get some improvement with ferrite...
  7. Merlin3189

    multimeter recomendations

    Just a thought: if you don't have an analogue meter, how about adding one of them to your kit? I still have a couple of these (now over 30 years old) which I use about as much as my digital meters (one nearly as old!) I can't really say that they are better, but I do like them for looking at...
  8. Merlin3189

    Questions regarding capacitors

    Well, firstly they don't say it can. They say, "IF" you assume it happens, then the value "can be calculated" The power stored in a 10 μF capacitor charged to 230 V can be calculated ... 0.26 Joules IF the energy is dissipated within 5 μs the potential power (generated?) can be calculated...
  9. Merlin3189

    Help with monostable and signals

    You're certainly doing the right sort of thing, but there seem to be some errors. In p1IWa (A) looks like (Xbar AND Qbar) when it should be (X AND Qbar) In oJdZe you show input B stays low, but still Q changes. Q can change only as a result of changes of B. In 7nERK I think you have (B) looks...
  10. Merlin3189

    Non Inverting amplifiers

    In these "negative feedback" circuits, there can be only a very small difference between the two inputs. If you increase the voltage on the non-inverting (+) input, the output voltage increases, then the voltage fed back to the inverting (-) input also increases. Although only a fraction of...
  11. Merlin3189

    A question on batteries.

    If we go with the idea that there is a +ve charge on one terminal of one battery and a -ve charge on the other terminal of the second battery, then I think you would get a current flow as you said. BUT if there's no where for the charges to go when they get to the other battery, you will very...
  12. Merlin3189

    Death by electricity

    Just wanted to say, the way I heard it was, "It's the Volts that jolts, but the mills what kills." mills being milliamps of course. I always think when I hear this sort of question (Volts vs Amps) that, if there's no current, nothing happens. It's always the current that counts: Volts, or...
  13. Merlin3189

    clamping circuits.......mechansim

    Clamping I'm not sure we have addressed the issue of clamping. This circuit is used (well, was used in pre-digital days) to establish an exact DC level for AC signals. The prime example in my experience was TV circuits: the varying modulation (AC) needed to be superimposed on a fixed bias...
  14. Merlin3189

    resistor question

  15. Merlin3189

    Flashing day/night indicator circuit

    Just as a start, maybe look at a these: A dark-activated switch http://www.zen22142.zen.co.uk/Circuits/Switching/darksw.htm and a simple flasher circuit that could go in place of the relay http://www.reprise.com/host/circuits/transistor_flasher.asp The particular transistors here are not...
  16. Merlin3189

    Transistor Output Voltage Formula

    Transistor collector Voltage Looking at the circuit you show, I would say the output Voltage is not critical. This appears to be a buffer inverter stage for a switching Voltage that is intended to be either on or off. With the 5V input you should get a low output, a few tenths of a Volt. If...
  17. Merlin3189

    2 step motors on one chipset

    Sorting machine Your outline design sounds good to me. I like the way you have broken the solution into stages, which could be built and tested as modules. -Parallel port sounds good to me. I have built projects controlled from a parallel port and they worked well. I think these days you...
  18. Merlin3189

    Piezo electricity

    Ummmmm? If no resistance, where's the energy coming from? I think you may be under the misapprehension that no work is done on a Piezo crystal when you compress it. You obviously have to apply a force, and the crystal has to deform, even if very slightly: that's work. If some of the...
  19. Merlin3189

    transformer observation

    Perhaps I chose the wrong smiley for my comment?:p What I was saying is, that he did not mention a load for the current to flow through. We now know that the load is, " a short circuit through a ammeter ", ie. a very low DC resistance (probably non-linear) with an indeterminate reactance. (Was...
  20. Merlin3189

    transformer observation

    Can you explain what you mean by this? I don't see how the material of which the primary is made can affect the current in the secondary. How does the primary DC resistance of your iron coil compare with that of the copper coil? Does the secondary open circuit Voltage change? If not, do you...
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