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  1. KrisBlueNZ

    capacitor replacement

    Yes, Dave and Steve are right, I did jump the gun, and if the capacitor is not connected between Phase and Neutral, or across the primary of the mains transformer, as described in post #1 ("across a transformer"), then Adam and Harald are right that it needs to be a Y-rated cap, not X-rated.
  2. KrisBlueNZ

    Turns on LED upon receiving IR signal

    How about using those coloured plastic rings that you slide over the grip part of the key? You can get them in about ten different colours. Then just stick a piece of coloured plastic, or some paint, on the door near the lock. Then you just match the colour on the key with the colour on the...
  3. KrisBlueNZ

    capacitor replacement

    Right, as Harald says, capacitors designed for direct connection across the AC mains have special characteristics. They are divided into four classes: X2, X1, Y2 and Y1. See https://en.wikipedia.org/wiki/Film_capacitor#AC_voltage_and_current. You can use any of those types for connection across...
  4. KrisBlueNZ

    Triggering a 555 timer on opening of a line

    Hi zookopf and welcome to Electronics Point :-) I'm sure we can help you, but you need to explain your problem more clearly. If you add the timing components to the 555, your circuit will generate a pulse when the contacts at the input go open. You could use a relay, with its coil connected...
  5. KrisBlueNZ

    lives circuit

    No problem :-)
  6. KrisBlueNZ

    voltage "clamp" when input analog signal removed

    Yes, I was wondering about that as well. I didn't follow the description very well but that part seemed more confusing than the rest. I hope the diagram will clarify this!
  7. KrisBlueNZ

    Confusing Relay-Relay Connection .. pls help

    I can't find a data sheet for the MY3NJ; only for some versions of the MY2 and MY4. I don't know what's wrong. My guess is that you're connecting something wrong but I don't know for sure. I suggest you try a different relay.
  8. KrisBlueNZ

    voltage "clamp" when input analog signal removed

    Can you draw up a diagram please. Include as much information as you can - part numbers, especially.
  9. KrisBlueNZ

    Confusing Relay-Relay Connection .. pls help

    So you're saying that when the 3PDT relay coil is energised through the receivers, the built-in LED indicator turns on for a second then goes out, although the lamp and the siren keep going? And when the 3PDT relay coil is energised directly from a 12V supply, the built-in LED indicator works...
  10. KrisBlueNZ

    741 as differential amplifier

    Yes, for a gain stage, input offset voltage causes an offset at the output which is equal to the input offset voltage multiplied by the stage gain. Here's an op-amp differential voltage amplifier: It accepts two voltages on its two inputs, nodes A and C, and generates an output voltage on...
  11. KrisBlueNZ

    Confusing Relay-Relay Connection .. pls help

    They are all equally suitable. Buy whichever one is cheapest, or is already used in another part of the project. BTW I was kidding about the "Sir" bit. Neither Harald nor I are old enough, rich enough, or noble enough to be called "Sir" :-) You don't need to use that word.
  12. KrisBlueNZ

    Confusing Relay-Relay Connection .. pls help

    Sir Harald is away at his castle, hunting foxes and talking to his subjects. But Sir Kris can answer your question. ;-) He's wrong. Perhaps he doesn't understand the question. You should have a back EMF suppression diode across the coil. A relay coil is inductive. When current to the coil is...
  13. KrisBlueNZ

    voltage "clamp" when input analog signal removed

    Hi Skippy. As you say, a pullup resistor would work if the connection is broken, but it may not work if the voltage source loses power. It depends on the characteristics of the voltage source. One way to find out would be to test it. Connect a pullup resistor, make sure it doesn't...
  14. KrisBlueNZ

    741 as differential amplifier

    ±5~10% of what? The full scale current? Let's assume ±10%. If the current flow was 40A, a measurement between 36A and 44A would be acceptable, right? OK, that tells you about the gain tolerance of the circuit, but not the offset tolerance. If the current flow is, say, 0.4A, would you need the...
  15. KrisBlueNZ

    lives circuit

    The CD4015 (http://www.digikey.com/product-detail/en/CD4015BE/296-2035-5-ND/67249) does not need programming. It's a dual 4-bit shift register with parallel outputs. Here's how you use it to drive up to eight LEDs. Tie both Reset inputs together. They must be driven high briefly when the game...
  16. KrisBlueNZ

    Level signal compatibility?

    No, it most likely won't. The transistorised versions of the 74nn logic family (74nn, 74LSnn and a few others) use "totem pole" outputs and do not pull high strongly. This is why the low and high voltage levels for these families are skewed towards 0V - they are typically 2.4V and 0.8V - rather...
  17. KrisBlueNZ

    741 as differential amplifier

    This one is worth a look: Analog Devices AD8217: http://www.digikey.com/product-detail/en/AD8217BRMZ/AD8217BRMZ-ND/2404124 USD 2.89 Input offset voltage 0.25 mV at room temperature; this is 1.25% of a full scale of 20 mV. The ZXCT devices have pretty poor accuracy specifications. The best of...
  18. KrisBlueNZ

    Ideas to check continuity

    If you need to check for shorts, connect them as described by shumifan but skip every second track, and repeat the same pattern for the tracks you missed. Then you just need to check continuity of each S-pattern and for shorts between the two S-patterns. (This assumes that shorts will be between...
  19. KrisBlueNZ

    lives circuit

    Without ICs? And you're making a handheld game? Are you a masochist?
  20. KrisBlueNZ

    741 as differential amplifier

    Input offset voltage is an error due to imperfections in the op-amp. To understand input offset voltage, you need to understand what an op-amp does, and how the differential amplifier circuit works. I don't have time to explain it here and now! In simple terms, the input offset voltage causes...
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