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  1. KrisBlueNZ

    Solenoid Back EMF

    Right, so assuming perfect switching and no losses anywhere, the first voltage peak is when all the magnetic energy from the inductor has been transferred to the capacitor, right? So for Adam's inductor: L = 0.0206H I = 0.5A Calculating energy in the inductor: E = I^2 L / 2 = 0.25 * 0.0206 / 2...
  2. KrisBlueNZ

    transistors for cap charge pump

    Oh. That's different. The only way to save your batteries is to minimise inefficiencies. You cannot create energy out of nothing. If you charge capacitors in series with the load, the energy that goes into those capacitors is not available to the load. There's no such thing as a free lunch...
  3. KrisBlueNZ

    transistors for cap charge pump

    The type of circuit you're describing is called a switched capacitor charge pump. Switching circuits aside, it may not be suitable for what you want to do, and here's why. Take a 2200 µF, 25V electrolytic capacitor that has been charged up to 12V. Now start drawing a current of 10A from it. The...
  4. KrisBlueNZ

    Solenoid Back EMF

    Right. I don't know how to calculate that :-(
  5. KrisBlueNZ

    voltage divider transistor biasing...

    I calculated an estimate using the slope of the line on the Ic vs. Vbe graph in the Fairchild BC550C data sheet: http://www.fairchildsemi.com/ds/BC/BC546.pdf - Figure 2 on page 2. The Y axis is Ic, not Ib, so you have to assume some figure for hfe. I looked at the section of the graph between...
  6. KrisBlueNZ

    Bridge rectifier help please

    I don't know. It depends how the transformer is current-limited. I have no experience with very-high-voltage transformers so I can't answer, I'm afraid. But I can say that the fact that the transformer is rated for 30 mA doesn't necessarily mean that it won't deliver more than that. Right. I...
  7. KrisBlueNZ

    voltage divider transistor biasing...

    Re the change in cutoff frequency: the "cutoff frequency" is not the frequency below which signals will be "cut off"; it's only the -3 dB frequency. The stage has a lot of gain so having a -3 dB frequency that's not outside the designed frequency range is not necessarily a problem at all. Not...
  8. KrisBlueNZ

    Solenoid Back EMF

    The diode's voltage rating needs to be comfortably higher than the voltage applied to the coil, because when the coil is energised, the diode is reverse-biased and has the applied voltage across it. The diode's current rating needs to be comfortably higher than the current flowing in the coil...
  9. KrisBlueNZ

    transistors for cap charge pump

    It would be helpful if you gave us some more information. How many capacitors? Is the 24V the voltage across each capacitor, or across all of them in series? What capacitance values?
  10. KrisBlueNZ

    voltage divider transistor biasing...

    Sorry, my mistake. You were clear; I didn't read properly. Cool :-)
  11. KrisBlueNZ

    Bridge rectifier help please

    I guess he wants to put a resistor in series with them to limit the inrush current to avoid damaging the diodes. If that's the case, the total resistance needs to drop the peak secondary voltage (12 kV * sqrt(2) which is 17 kV) at 30 mA, so from Ohm's Law, R = V / I = 17000 / 0.03 = 570 kilohms...
  12. KrisBlueNZ

    Touch dimmer slaves - how do they work?

    I think Graham is suggesting that there may not be a protocol. Although the Master device presumably does have a microcontroller, the slaves just need to provide a single true/false indication - either the touch pad is being touched or it isn't. So it could just be an open collector bus or the...
  13. KrisBlueNZ

    voltage divider transistor biasing...

    I don't know what you mean by a maximum "voltage drop across the collector" and you can't get 8V from a 6V source. Base current is not a critical number in the calculations. Current gain for an individual component type can vary over a 2:1 ratio or even wider, and is affected by temperature as...
  14. KrisBlueNZ

    RS232 to TTL

    Sounds all good to me.
  15. KrisBlueNZ

    Basic PCB Boards for use with a microcontroller

    Hi there and welcome to Electronics Point :-) As Steve says, veroboard (aka stripboard) is a good option for prototypes and one-off projects. It works best with through-hole devices (devices with pins on a 0.1 inch grid that go through holes in the board); many PICs are available in...
  16. KrisBlueNZ

    Another treadmill problem

    OK. It looks like something on the daughter board is feeding voltage from the 12V rail back onto the 5V rail. I really need to trace out the schematic (circuit diagram) of the daughter board. How would you feel about desoldering and removing the daughter board, and posting it to me here in New...
  17. KrisBlueNZ

    touch sensitive wire?

    What will the wires be touched by? It's pretty easy to detect the voltage that is coupled into a wire, or the sudden increase in capacitance, when it is is touched by something conductive (or partly conductive) such as a person's skin. The person doesn't have to be connected directly to...
  18. KrisBlueNZ

    Bidirectional Data Line Circuitry

    BTW I suspect contacts are not going to be a workable solution here, and in any case you would be better to start from an overview of the requirements and work downwards towards the implementation details instead of starting by focussing on one aspect of the implementation; it's easy to...
  19. KrisBlueNZ

    RS232 to TTL

    Some 3.3V devices are "5V-tolerant" (specifically designed to be able to accept 5V signals) and will not be damaged. You need to look on the data sheet for your microcontroller. (Or you could tell us what it is.) Maxim (and others) make lots of RS-232 interface devices that can be powered...
  20. KrisBlueNZ

    Bidirectional Data Line Circuitry

    I think the problem is messier than that. A cube doesn't know when another cube might be trying to transmit to it. When the cube isn't connected to another cube on a particular face, it can transmit a short "I'm here" message at irregular intervals, for example with each delay chosen randomly...
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