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  1. KrisBlueNZ

    741 as differential amplifier

    Have you rejected the Honeywell parts that Olivier mentioned in https://www.electronicspoint.com/threads/measuring-high-current-with-pic.269135/#post-1612699 and the Allegro devices I mentioned in https://www.electronicspoint.com/threads/measuring-high-current-with-pic.269135/#post-1612711 ...
  2. KrisBlueNZ

    DipTrace PCB software

    Protel for Windows 2.8. Dated April 1995. I tried installing it using compatibility modes but no go.
  3. KrisBlueNZ

    LED Screen

    Yes, I've tidied it up a bit and posted it as a resource, at https://www.electronicspoint.com/resources/saturation-in-transistors-bjts-why-and-how.28/ Comments welcome as usual. Yes, I meant to mention that. It's really the best option, especially if you're switching a high current load and the...
  4. KrisBlueNZ

    Saturation in transistors (BJTs) - why and how

    When a bipolar junction transistor (BJT) is used to switch a load (e.g. a relay, an LED, a buzzer, a small motor, etc) ON and OFF, it is most often operated as a "saturated switch". This article explains saturation in BJTs - why it is used, and how to calculate the base resistor to ensure...
  5. KrisBlueNZ

    Saturation in transistors (BJTs) - why and how

    KrisBlueNZ submitted a new resource: Saturation in transistors (BJTs) - why and how - The reason you would saturate a BJT, and calculating base current and resistor values Read more about this resource...
  6. KrisBlueNZ

    DipTrace PCB software

    There isn't an appropriate category. Perhaps Ian could allow us to add categories. Yes, I have used PFW 2.8 since it came out. It has a few bugs but they're consistent and avoidable, and it's quick to use and has all the features I need. I run it on Windows 7 x64 under Windows Virtual PC...
  7. KrisBlueNZ

    Electronic angle finder repair

    A quick Google shows that they consist of two arms that pivot at the point where they join together. So I assume they have a rotary encoder at the join. But some photos would be very helpful.
  8. KrisBlueNZ

    LED Screen

    Here's how I calculate the required base resistor for a common emitter circuit where the transistor needs to be saturated. Calculate the maximum collector current (IC) divided by the minimum current gain (hFE) from the data sheet for that collector current. You say IC = 30 mA and hFE(min) = 83...
  9. KrisBlueNZ

    DipTrace PCB software

    Agreed. When Ian is back from his holiday I will mention it.
  10. KrisBlueNZ

    Choosing an Opto Isolator

    This one looks suitable: http://www.digikey.com/product-detail/en/CPC1708J/CLA279-ND/1277134 It's rated for 4A which seems like overkill, but it's the cheapest that Digikey have. Its input pins connect to an internal LED, so your control voltage will need to go through a resistor to limit the...
  11. KrisBlueNZ

    DipTrace PCB software

    I just recently did a survey of EDA packages for schematic capture and PCB layout. I haven't tried these out; if anyone does, please post your opinions. Free and budget: 123D Circuits - Web-based AutoTRAX DEX 2020 (http://www.dex2020.com/) - Free trial; full price USD 49 DesignSpark...
  12. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    That device doesn't convert colour to frequency... it converts light intensity to frequency Sorry, I spoke too soon. I'll keep reading the data sheet. OK, so the TCS3200 and TCS3210 are 8-pin SOIC devices that contain an array (8x8 for TCS3200; 6x4 for TCS3210) of photodiodes with coloured...
  13. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    Part number? Link to data sheet? What do you want the PIC to do with the information? What other functions will it be performing?
  14. KrisBlueNZ

    555 to Power a Solenoid

    You already have the diode across the solenoid in your diagram in post #1.
  15. KrisBlueNZ

    555 to Power a Solenoid

    Hi Angus and welcome to Electronics Point :) A 2W solenoid at 9V will draw 222 mA. So you should use a transistor rated for at least 300~400 mA. Depending on where you live, one of the following will be readily available: BC337-40 Fairchild 0.8A 45V...
  16. KrisBlueNZ

    Why does this LED light up?

    You're welcome :-)
  17. KrisBlueNZ

    DS1307 initializing

    OK, here's ds1307_init(): 01 void ds1307_init(void) { 02 int seconds = 0; 03 I2C1_Start(); 04 I2C1_Wr(0xD0); // WR to RTC 05 I2C1_Wr(0x00); // REG 0 06 I2C1_Start(); 07 I2C1_Wr(0xD1); // RD from RTC 08 seconds = Bcd2Dec(I2C1_Rd(0)); // Read current...
  18. KrisBlueNZ

    DC Regulated Power Supply Kit

    Hi Larry and welcome to Electronics Point :-) Are you sure the kit is made by "Calectro"? The only Calectro I can find is a Swedish company that makes HVAC components! Can you check the spelling? Can you upload a scan or photo of any paperwork that came with it?
  19. KrisBlueNZ

    Why does this LED light up?

    Hi Jose and welcome to Electronics Point :) Your flip-flop is powering up in the activated state. This could be due to leakage currents, or stray capacitance - through the breadboard, for example. Try shorting the base and emitter together on one transistor (it doesn't matter which). This will...
  20. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    That's a bit different from the simple methods I suggested - it accepts an analogue signal, which may contain many frequencies, and performs simple digital signal processing on it to determine whether the detection frequency is present in the input signal or not. It does not determine the...
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