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Everything posted by pebe

  1. Feed the 555 output into a CD4026B. That will give you a 16 stage counter with 7segment output. Use the chip's 'carry out' to cascade further 4026 ICs if you require more than one 7segment display.
  2. According to the manual, there is a control marked 'SWP.VAR' (marked 30 in the diagram that shows layout of controls) that allows the sweep to be made variable. Have you set it correctly?.
  3. Behind each of the four fans you could put a thermistor and wire them all in series. Feed them through a current limiting resistor from a voltage source. Power will be dissipated in them and they would normally get warm, but the fans will keep them cool. Monitor the voltage across the thermisters. Failure of one or more fans will result in a change in that voltage.
  4. Anyone wanting to build a variable power supply, without all the problems of series regulation, would do well to take this Switch Mode route. http://www.instructables.com/id/Build-your-own-Variable-Lab-Bench-Power-Supply/
  5. Like I asked, at which.......................?
  6. At which of the three academies of excellence you attended did you learn this nebulous waffle?
  7. Are you saying that the driver should be prevented from adjusting his seat when driving? Simple, - shackle the adjustment bar with a padlock! But surely, this question does not belong on an electronics forum?
  8. I cannot understand why you would want to 'lock' a car seat. Is that to prevent someone sitting in it, or prevent someone stealing it?
  9. ????????? Could you explain more, please?
  10. QUOTE "i'm asking as i've been working on a design that to my understanding should've worked. i have a generic NPN restoring the supply voltage and feeding it's emitter output to a 2N2222 parallel to a charging capacitor for a delayed avalanche. somehow the avalanching only works when i swap the 2N2222 + charging capacitor sub-circuit to the collector side. it surprised me as when it was connected to emitter, it was also directly connected to ground. and when it was on the the collector side it was directly connected to the supply. so it was not isolated and would be biased to a common ground. although, as a side note, when it was on the emitter side, the charging capacitor might have caused a reverse current through the generic NPN and leaking to other parts of the circuit. so i probably should've put a diode in there. well i didn't get the chance to as i blew my 2N2222, so now i have to go to my local supplier to have more. charging". Are you suggesting that a circuit would not be better understood this convoluted description? (Note to Admin. Although I can get into the editing section, there is no way I can edit or cancel my post, so I am restating it. Also, you have no 'preview' button).
  11. Some sound on the video stating the problem would have helped.
  12. If you are using the transistor as a switch, it makes no difference provided you can apply enough base bias to get the transistor into its saturated state.
  13. How about providing a circuit. One picture is worth a thousand words!
  14. pebe

    question about PIR

    It may be one of these. http://www.bitsbox.co.uk/data/es0550.pdf
  15. I am surprised that you would get excessive vibration in a glider. No chance of mounting a camera on a light elastic suspension, I suppose?
  16. Could you 45degree angle a small mirror in front of the lens?
  17. Where are you going with this discussion? Your posting is not meaningful unless it is aiming for a conclusive point. So far, I have not seen anything about the subject of the thread, ie. "comparator for DC voltage".
  18. Unless you are dead keen to make one yourself, have you considered buying one of these very cheap Chinese camcorders? You couldn't make anything as light and as cheap. http://www.ebay.co.uk/itm/Mini-MD80-DV-Camcorder-DVR-Digital-Video-Recorder-Sport-Camera-SPY-Hidden-Webcam-/201208835814?pt=UK_AudioTVElectronics_Video_Camcorders&hash=item2ed8fb2ee6 http://www.ebay.co.uk/itm/Smallest-Mini-5MP-HD-DV-Spy-Digital-Camera-Video-Recorder-Camcorder-Webcam-DVR-/141075746093?pt=UK_AudioTVElectronics_Video_Camcorders&hash=item20d8c50d2d
  19. The current through resistor Q is zero. Your circuit is meaningless.
  20. If I may add to Kevin's comments: There is a circuit that would not only supply inverse reactive current for use in unilateral phase detractors, but would also be capable of automatically synchronizing cardinal grammeters. Such a circuit is the "turbo-encabulator." Basically, the only new principle involved is that instead of power being generated by the relative motion of conductors and fluxes, it is produced by the medial interaction of magneto-reluctance and capacitive directance. :)
  21. As Audioguru has already explained, the 'ground' in a circuit is merely a reference point against which all other voltage nodes in the circuit are measured. It does not push or pull anything. It may or may not be connected to true ground (earth), or to the earthing point in an electric mains supply system, or to a metal chassis on which the circuit is constructed. You cannot get any simpler than that.
  22. Kevin, if you are referring to your first circuit in this thread, it cannot work. The Vbe of the Darlington will always be around 1.5V so the voltage across the 20K resistor will be about 135mV. Ignoring the input offset, the two input voltages of the op-amp must be the same, so the output voltage will therefore settle at Vset minus 135mV, and there is no way you can get it any higher. If you change the values of the two feedback resistors to alter its gain, the output voltage will lie somewhere between Vset and Vset minus Vbe, and as Vbe varies with load, then so will the output voltage.
  23. Every time you use an auto-ranging meter it goes through the timewasting procedure of starting at the highest range and then scaling down through the ranges until it finds a range suitable for display, so there is little risk of damaging the meter by over-voltage/current. If you move your probe to a point 0.5v higher and it will go through the same procedure again. The first DMM I ever owned was an auto-ranging type. But it had a button on it that enabled it to hold the setting of the previously used range. Had it not been for that, it would have been a very frustrating meter to use. I much prefer a switched-range type.
  24. These are the faults I found: The timer is described in the parts list as ‘a standard NE555 timer chip’. It is powered by 2 x 9V batteries. But that is the absolute maximum voltage rating for many of these chips, and exceeds the 16V absolute maximum of a Fairchild or Contek NE555. R4 is shown shorted out so Q2 is switched hard on during the 0.2sec pulse. It cannot oscillate under those conditions. The circuit shows on its legend ‘Page 1 of 3’, so perhaps there is more. Certainly, I would have expected to see a recommended layout to prevent possible interaction between the various inductors. EDIT: My previous statement about problem with 555 output going high was not valid, so is now removed. I have now found details of the 555 circuitry. When output pin3 is high (sourced) and its load is connected to a voltage higher than its source voltage, the output goes O/C. Sorry about that :-[
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