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  1. KrisBlueNZ

    LED's turning on if hand crosses area.

    Not sure if this is relevant, but this problem description reminds me of a problem I had once that turned out to be caused by LEDs responding to light from my desk lamp. In my case, when this light fell on the LEDs, they would generate a voltage, which would bias the input circuits of a...
  2. KrisBlueNZ

    New Member Here......

    Hi Andy and welcome back! I'm sure you'll be able to help. We get all kinds of questions here. You never know when one will come along that's right up your alley. Regards Kris
  3. KrisBlueNZ

    Old transistor magnetometer

    Hi Nick and welcome to Electronics Point :-) Wow! It's a loooong time since I've seen transistors drawn like that! I think there's something wrong with TR4. Its base can never be pulled "below" 0V so its collector shouldn't connect to the 0V rail unless it's an NPN, and the symbol and parts...
  4. KrisBlueNZ

    Temperature compensating a transistor?

    Interesting comments Adam. Sometimes I wish I understood the physics, so I could understand WHY you see these odd behaviours, like the low saturation voltage and the faster switching.
  5. KrisBlueNZ

    transistor amplifier with the common emitter configuration

    There are various ways to calculate them, but a good place to start is to choose the collector current. A typical collector current for a small-signal amplifier is a few milliamps. If there's a need for low output impedance, a higher current can be used, and if there's a need for low current...
  6. KrisBlueNZ

    Transistors

    I'm with you so far. And that was what I was taught. Yes. I don't know of any other justification. And I think it's sufficient justification. I certainly think it's more sensible to explain that Vbe causes Ib with an exponential relationship, then Ib causes Ic with a roughly direct...
  7. KrisBlueNZ

    transistor amplifier with the common emitter configuration

    Hello and welcome to Electronics Point. I have moved your post from the Circuit Help forum to the Electronics Homework Help forum. 1. Check the polarity of your supply voltage. Also, the supply voltage source is usually shown at the right hand side, not at the top like that. 2. Your resistor...
  8. KrisBlueNZ

    Temperature compensating a transistor?

    Sure. Here's a screen cap of the schematic and the simulation. The green trace is the control voltage, which ramps from 0V to 9V. The blue trace is VC, the voltage at the top of C1. There are several changes from the OP's circuit: R7 is needed because the comparator output pulls high only...
  9. KrisBlueNZ

    Help please

    Right of the control knob, there's a three-terminal device marked IC2 78L06. It looks like it's suffered a hernia of some kind on its left hand side. Can you confirm this?
  10. KrisBlueNZ

    Help please

    OK, thanks for the pics. When the unit was repaired in the past, was it just the circuit board that was replaced? The circuit board has some LED indicators. Do they stop working when the unit stops working? There are eight wires connecting to the board. Can you list what they connect to? I...
  11. KrisBlueNZ

    Help please

    Log in to photobucket.com and click the image so you can view it on its own page. On the right side, at the top of the page, is a box headed "Links to share this photo". Click the URL in the "Direct" link and it will copy it to your computer's clipboard. Then when you're editing your post, click...
  12. KrisBlueNZ

    Help please

    Try one of the free image hosting sites listed here: http://webtrends.about.com/od/prof4/tp/Free-Image-Hosting-Sites-For-Photos.htm I use http://www.photobucket.com. It's free and seems to be well suited to this application.
  13. KrisBlueNZ

    preamplifier justifications

    Yes you should definitely check out that thread that Steve linked to, and you should Google relevant keywords - best books to learn electronic design, etc - to try to find other people's recommendations. I'm afraid I don't have any recommendations, apart from Art of Electronics (#3 below). I...
  14. KrisBlueNZ

    Barcode reader IC

    Hi there and welcome to Electronics Point :) I don't think you'll find a single IC that will do that job. There are multiple parts to a bar code reader and many of them can't be manufactured onto an IC. You need to Google bar code reader module.
  15. KrisBlueNZ

    preamplifier justifications

    Hello Ken. Don't be offended, but... If you don't know the answers to those questions, you are a long way from being able to design your own sound system. I suggest you start by getting some intermediate electronics texts that will give you a real understanding of principles and components...
  16. KrisBlueNZ

    12v Powerbox for Camping/fishing

    Here are some calculations. Battery capacity: 14 Ah @ 12V = 168 Wh. Treat this as a maximum; a typical figure might be 140~150 Wh. Mobile phone charger 1A @5V = 5W ÷ 0.7 for 70% converter efficiency = 7.2W * 4 hours to recharge (sounds about right) = 29 Wh. I don't know how much power your...
  17. KrisBlueNZ

    12v Powerbox for Camping/fishing

    I recommend fusing each outlet separately. For this application, PTC resettable fuses are a good idea. See http://www.digikey.com/product-search/en/circuit-protection/ptc-resettable-fuses/656272?stock=1 and for some typical components...
  18. KrisBlueNZ

    Unknown part

    Well at least they're up front about it!
  19. KrisBlueNZ

    Help for buying Digital Multimeter

    I think he's asking whether anyone can upload photos of the insides of either of those multimeters. My advice on choosing multimeters is old but still good: Buy a Fluke!
  20. KrisBlueNZ

    switch that turns off upon trigger

    Hi Mariano, and welcome to the Electronics Point forums :-) I'm afraid I can't understand what you have, and I can't understand what you want to do! It's a bit confusing that there is a selector switch and another switch, which seems to be some kind of sensing switch to trigger the alarm, is...
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